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Olivier Biot
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Reged: 04/25/05

Loc: 51°N (Belgium)
My very late 14 inch f/5 project...
      #3956758 - 08/01/10 06:53 AM Attachment (500 downloads)

Time to post some photos of the project as it stands today.

I have the optics, the secondary holder, and a low profile helical focuser.

I have lots of wood that has been cut long time ago, I hope I can reuse part of it.

First photo: UTA (heavy, bulky) with melamine light shield standing on top of a high mirror box:


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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3956759 - 08/01/10 06:53 AM Attachment (252 downloads)

View from where the focuser should go:

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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3956762 - 08/01/10 06:55 AM Attachment (224 downloads)

Without the light shield you can see the structure of the UTA. It's made of 18mm plywood (Lauan?) and held together with 20mm x 20mm square aluminium struts and angle profiles, everything bolted together (no gluing or welding):

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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3956763 - 08/01/10 06:57 AM Attachment (180 downloads)

The four bolts on top of the pink foam pads are the location of the focuser. The foam pads allow for collimating (squaring) the focuser to a certain extent.

Another view of the same, with the secondary mirror holder in place. Manufactured by Gary Wolanski (Canada) at the end of the 1990s (shame on me!):


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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3956764 - 08/01/10 06:58 AM Attachment (168 downloads)

A view through the UTA:

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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3956767 - 08/01/10 07:02 AM Attachment (158 downloads)

The secondery holder has a built-in offset so the diagonal is a bit farther from the focuser. The light cone is indeed intercepted at different aperture of the converging cone sent by the primary mirror.

Here's a close-up where you can also see how the spider vanes are attached to the UTA:


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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3956770 - 08/01/10 07:05 AM Attachment (187 downloads)

A close-up of the offset secondary holder and secondary collimation screws:

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andypod
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Reged: 04/07/09

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3956787 - 08/01/10 07:36 AM

Thats a very nice looking UTA Olivier. How heavy is it exactly??? It looks quiet heavy.

Andy


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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: andypod]
      #3956792 - 08/01/10 07:47 AM

It not only looks heavy, it is. Without anything more it's 3kg: 2.5kg for the cage, 0.5kg for the shield.

Focuser, mirror, telrad, ... will add at least 1.5kg to the weight. ence the weight MUST go down


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a__l
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Reged: 11/24/07

Re: My very late 14 inch f/5 project... new [Re: andypod]
      #3956794 - 08/01/10 07:53 AM

The plywood 18 mm is superfluous for such diameter. There is enough 12 mm. It is additional weight.

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Mirzam
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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3956799 - 08/01/10 07:57 AM

Using single rather than paired struts coupled with a focuser board made of wood may help cut some weight. Also, a lightweight focuser like a KineOptics would help. Or you could go with a single ring design.

http://www.kineoptics.com/HC-2.html

JimC


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Sky Captain
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Re: My very late 14 inch f/5 project... new [Re: Mirzam]
      #3958303 - 08/01/10 11:19 PM

Construction looks great Oliver!

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rboeAdministrator

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Re: My very late 14 inch f/5 project... new [Re: Sky Captain]
      #3958992 - 08/02/10 11:50 AM

I used four cherry dowels as struts on one upper cage. Then I routered a groove in the plywood ring to house the laminage (royal pain to put together but once done it became a structural member) then morticed in slots to hold the focuser board made from aircraft grade thin plywood. Very strong and light.

Turned out it was too light for the scope so it has never been used as I have not started rebuilding the rest of the scope.

Looks like I'll be going in a different direction so it will probably never get used. sigh.


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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: rboe]
      #3959210 - 08/02/10 01:41 PM

The struts are aluminium, hence they don't really add a lot to the weight.

I definitely need to make the UTA lighter and slimmer. What's more challenging, are the 2 plywood rings. Not sure if opting for bike rims is a good option.

Regarding truss pole attachment I really like what Kerry did, but I don't think this is feasible for me right now.

Tonight I'll be finalizing the overall CAD drawings of the scope. This way I can start checking my inventory of plywood for availability.


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rboeAdministrator

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3959253 - 08/02/10 01:59 PM

Aluminium is very light but you have eight of them, I think you could safely purge four of them. After all a sheet of paper is pretty light but you wouldn't want to be hit by a ream of them!

I think I used 1/2" (~13mm) baltic birch for my rings. At least as strong as your choice due to the thinner plies - and more of them.

I would have you review the way you fasten the al. struts, perhaps go to a single through fastner instead of the braces. You could drop four parts and six fasteners that way.

With four Al. struts you can fasten the spider to them and same the parts that you are using now (changing the number of rings or dimensions as suggested will negate that depending on how you go about it).

You could look at a single ring or a dua ring but reduce the distance between them to the size of your focuser. Opposite the focuser you'll have to have an over sized light shield like Kerry did.

Push come to shove, I think you could find a lighter secondary holder too but that one seems pretty good so I would not be in a hurry to ditch it unless you have to.


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Jack Day
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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3959401 - 08/02/10 03:18 PM

Looks great, but I am curious on the design of your spider. Won't you end up with eight sets of diffraction spikes? The vanes of the spider are not lined up...

Edited by Jack Day (08/02/10 03:22 PM)


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a__l
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Reged: 11/24/07

Re: My very late 14 inch f/5 project... new [Re: Jack Day]
      #3959450 - 08/02/10 03:42 PM

Rboe writes about a correct direction for modernization...
In practice it is the basic ideas from the book K&B.


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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: Jack Day]
      #3959639 - 08/02/10 04:59 PM

Quote:

Looks great, but I am curious on the design of your spider. Won't you end up with eight sets of diffraction spikes? The vanes of the spider are not lined up...




If the vanes are parallel and perpendicular, then there will only be 4 spikes. Otherwise there will be a multiple of 4

Eventually I'd go for a curved spider (no visible spikes), but that won't happen for Mk I


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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3959650 - 08/02/10 05:01 PM

Thanks for your input Ron! I'll dramatically reduce the height of the UTA. I just keyed in again my numbers in NEWT (I previously computed all this by hand over 10 years ago), and the numbers are right

The UTA will have an inner diameter of 406mm (16"). That will be perfect for the 14" primary .


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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3959675 - 08/02/10 05:09 PM Attachment (142 downloads)

Okay, time to see how the puzzle fits together piecewise now.

Here's an image showing the dimensional constraints for my cell. The green zone is the safe zone, the red zone is the "danger zone" where my mirror cell protrudes.

All dimensions are given in millimeters, rounded to 0.1mm.


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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3959693 - 08/02/10 05:16 PM

If you look closely you'll see the dimensional constraint space is rectangular. It's narrower left-right, and wider top-down.

The "vertical" clearance I need is at least 107.6 + 107.6 + 215.2 = 430.4mm. It is determined by the triangular cell support. I was thinking to use 440mm. That still gives me 9mm of play, which I believe is safe.

The "horizontal" clearance I need is at least 372.7mm. It is determined by the lateral support system of the mirror. This is almost 6 cm less than the "vertical" clearance.

Should I go for a "square" section of the mirror box, or should I go for the slimmer rectangular shape?


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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3959702 - 08/02/10 05:19 PM Attachment (79 downloads)

Here's an idea of what a mirror box with a "square" section and an inner space of 440mm would look like:

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Mirzam
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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3959862 - 08/02/10 06:03 PM

Hello Olivier,

Although the rectangular box may be more compact, the square allows more space for internal counterweights and batteries if needed.

JimC


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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: Mirzam]
      #3959956 - 08/02/10 06:53 PM Attachment (61 downloads)

Quote:

Hello Olivier,

Although the rectangular box may be more compact, the square allows more space for internal counterweights and batteries if needed.

JimC




That's an interesting thought!

So square it remains for now.

Here is a drawing with 400mm altitude trunnions in place:


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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3959975 - 08/02/10 07:04 PM Attachment (60 downloads)

Here's another rendering:

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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3959978 - 08/02/10 07:06 PM

Of course I have no clue where the altitude trunnions should be now, as I don't know the center of gravity of the scope yet.

I opted for 400mm trunnions since I have 2 400mm disks already. I believe they are large enough for a 14".


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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3959987 - 08/02/10 07:09 PM

I want to have a low profile rocker since I don't want to have to use a stool when I observe. That may be a bit challenging though if my COG is too high.

Also, the cell as I designed it today has this protruding triangle point to the bottom. I could reduce the size of the mirror box and trim part of the mirror box at the bottom if I don't make a full triangle but only use sections of it, attached to a metal frame. Maybe this is even easier to weld than my triangular cell.

The rocker I envision looks like Kerry's: a steel frame on which a low profile wooden trunnion support is attached.

I'll draw that frame tomorrow

Edited by Olivier Biot (08/02/10 07:32 PM)


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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3961475 - 08/03/10 01:09 PM Attachment (64 downloads)

One option is to eliminate protruding elements as much as possible. Here is a front view of the cell in the same square section mirror box, without the triangular U-profile unit that keeps the 3 pivots (visible in this image) in place:

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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3961536 - 08/03/10 01:34 PM Attachment (62 downloads)

A simplified option, which takes less real estate, and will allow me to have a smaller mirror box, is sketched below. The transparent yellow beams replace the triangular support and the black T-shaped collimation frame:

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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3961570 - 08/03/10 01:53 PM Attachment (52 downloads)

When compared to the option with the full triangular support, there's some gain:

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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3962006 - 08/03/10 05:47 PM Attachment (49 downloads)

Still struggling with a couple constraints for my cell.

Here's a simpler cell, where I removed the 45 whiffletree lateral support. This approach reduces the height of the cell of more than 2cm, and the height at the focuser will be impacted more since there are no more obnoxious "corners" in the way while moving in altitude:


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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3962010 - 08/03/10 05:47 PM Attachment (51 downloads)

Here's another view of the same:

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bertb
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Reged: 10/10/08

Loc: Achterveld, the Netherlands
Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3962990 - 08/04/10 04:50 AM

Look how Roel with his 12 inch F4 travel dobson designed his mirror cell. Very effective and easy to make!

Edited by bertb (08/04/10 04:51 AM)


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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: bertb]
      #3963610 - 08/04/10 01:16 PM

Thanks for that pointer Bert!

Anyway, I just realized I misinterpreted the lateral support performance figures for my mirror. The good news is that I can replace the bulkier and more complex 4 points whiffle tree support with a lateral support consisting of 2 bearings at 90 (45 from vertical at both ends).

Stay tuned for yet another picture of my slow progress


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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3963977 - 08/04/10 04:14 PM Attachment (55 downloads)

Here is tonight's iteration on the cell. I used angle L irons for the lateral supports. They can slide a bit sideways to adjust the manufacturing tolerances of the cell (slots). At the top there is a large washer that plays the double role of securing the lateral support in place and preventing the mirror from falling off the cell.

I will add 2 more identical clips to the top (where you can see the slots).

Image:


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Olivier Biot
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Loc: 51°N (Belgium)
Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3963988 - 08/04/10 04:20 PM Attachment (54 downloads)

Here's a close-up of the lateral support and mirror retaining clip in place. The white 'blob' represents the contact point. I was thinking about using some PTFE (Teflon) here:

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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3964003 - 08/04/10 04:25 PM Attachment (50 downloads)

Here's a view of option 3 in perspective:

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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3964064 - 08/04/10 04:52 PM

I have one question though: can this cell be made? The remaining issue I see now, is drilling the holes for the 3 pivots. Indeed, the 2 oblique U profiles cannot be drilled once they are in place.

Any thoughts?


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Benach
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Reged: 01/24/08

Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3964083 - 08/04/10 05:01 PM

Olivier: jups, can be made rather easy. You simply have to drill the holes before you weld the assembly. However, I have serious doubts about the edge supports. I strongly suspect it will wobble a lot. BTW, you can bond metal to glass without stress with RTV (Siliconenkit).

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rboeAdministrator

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Re: My very late 14 inch f/5 project... new [Re: Benach]
      #3964124 - 08/04/10 05:18 PM

Pre-drilling will cure any difficulties. But I don't see any play to allow the glass to expand (is it even needed? )

Are you going to weld the big U channels together?


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Benach
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Reged: 01/24/08

Re: My very late 14 inch f/5 project... new [Re: rboe]
      #3964145 - 08/04/10 05:27 PM

Rboe: me thinks the slots are for expansion. However, these can be much, much smaller than on this pic if they're for expansion only.

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rboeAdministrator

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Re: My very late 14 inch f/5 project... new [Re: Benach]
      #3964176 - 08/04/10 05:45 PM

I'm confused now. What slots? I only see the ones on the back of the channel and they aren't being used in this case.

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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: rboe]
      #3964237 - 08/04/10 06:23 PM

Quote:

Pre-drilling will cure any difficulties. But I don't see any play to allow the glass to expand (is it even needed? )




The glass should rest on those white blobs: they're the lateral support

The channels are there only so I can play with the ideal position of the lateral supports in the U beams.

Quote:

Are you going to weld the big U channels together?




Not me personally as I can't weld nor do I have the necessary equipment for doing so. But it is part of a job I will have to outsource. Hence I'm trying to design a 'simple' solution.


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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: Benach]
      #3964242 - 08/04/10 06:25 PM

Quote:

Olivier: jups, can be made rather easy. You simply have to drill the holes before you weld the assembly. However, I have serious doubts about the edge supports. I strongly suspect it will wobble a lot. BTW, you can bond metal to glass without stress with RTV (Siliconenkit).




I drew M8x70 bolts for the job. I don't know if there will be a lot of play.


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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: Benach]
      #3964247 - 08/04/10 06:29 PM

Quote:

Rboe: me thinks the slots are for expansion. However, these can be much, much smaller than on this pic if they're for expansion only.




No, they are not there for expansion. They're there only for allowing me to mess around with the ideal location of the lateral supports.

Depending on the type of material I will use in creating the contact point with the mirror, I'll have to move the lateral support beams a tad sideways to lower / raise the mirror in the cell. This might be overkill though, as collimation takes care of aligning optical and mechanical axes of the scope (as long as they're not too far off).

Hope this clarifies the reason of the slots on both U beams


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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: rboe]
      #3964249 - 08/04/10 06:30 PM

Quote:

I'm confused now. What slots? I only see the ones on the back of the channel and they aren't being used in this case.




There are slots on both parallel U channels. They may be concealed from view due to the lateral support hardware


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Benach
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Reged: 01/24/08

Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3964356 - 08/04/10 07:21 PM

Olivier: I seriously doubt this idea will work. If the telescope is pointing at an altitude near the horizon, the distance between the L-plates will become bigger because of gravity.
M8x70 bolts won't give enough friction for this idea. A member of my club recently had an elegant solution. Will try to get a picture of his solution and upload it here.


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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: Benach]
      #3979333 - 08/12/10 05:38 PM Attachment (68 downloads)

I ditched that approach now.

Here's a view at the collimation setup I'm considering now:


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Olivier Biot
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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3979337 - 08/12/10 05:40 PM

In between the 2 sets of locking nuts I will add a spring. The locking nut at the top must be loosened during collimation. I might have to come up with a better setup here though.

This setup will allow me to collimate the mirror cell from the front.


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Benach
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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3979353 - 08/12/10 05:46 PM

Can you show a pic from the front, this is not very clear to me.

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Re: My very late 14 inch f/5 project... new [Re: Benach]
      #3980896 - 08/13/10 01:44 PM

The square U profile is attached to the inside of the mirror box (I rendered the side panel in semitransparent blue). The mirror cell is mounted on a plywood board which has square metal tubing at each end. The metal tubing fits into the square U profile (and there's still a couple mm room on each side - I could add some Teflon or other plastic spacer there).

Between the U section and the square tube section I add a compression spring (not drawn in the picture above).

On the mirror box side rendered above, there will be 2 collimation bolts - you can only see the one in the front, then a couple bolts that attach the square U section to the plywood mirror cell base, and finally the 2nd collimation bolt.

On the opposite side (left, invisible), there will be 1 collimation bolt.

Try seeing only ONE hex nut above the square U section. It could even be a wing nut if you prefer That nut above the U section is then used for collimation.


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3981285 - 08/13/10 04:48 PM Attachment (53 downloads)

Here's a front view:

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3983815 - 08/15/10 05:38 AM Attachment (43 downloads)

Here's a couple views of one of the 3 the pivot assemblies of the mirror cell, rendered in perspective:

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3983819 - 08/15/10 05:46 AM

Each of those 3 pivots will be bolted to a 18mm thick plywood board. That's the 3 holes you can see in the bottom section of the square U section, bottom left view in the image above.

I'm still undecided about a couple aspects here:

1. My current design makes use of steel, the U profile has a 3mm wall thickness, and the square tube has a 2mm wall thickness.

I can have the same U and square tube sections in extruded 6060 aluminum as well. Should I stick to steel, or is aluminum a viable (and easier to drill/tap) option?

2. So far I drew the pivot axis as a bolt. Which hardware would be most suited here? A small bearing, a brass bushing, other?

3. Depending on (2) above, will I need to add spacers between the U section and the square tube section? If so, which material would you recommend?


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3983836 - 08/15/10 06:10 AM

Olivier: 1) Aluminium is for most telescope purposes just excellent. Nearly no dynamic behavior so no need for steel.
2) Use by all means stainless steel hardware. It does not really matter which type of hardware you want to use although I personnaly have a strong preference for countersunk holes. However, if you want to use Stainless steel, you have to anodise the aluminium. Otherwise it is likely you'll make a galvanic element which will cause fretting and/or corrosion.
3) if you intend to anodise the whole lot, brass or bronze is fine. Small pieces of teflon as well.


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Re: My very late 14 inch f/5 project... new [Re: Benach]
      #3983848 - 08/15/10 06:15 AM

Thanks for your input!

Anodizing is not in my reach, hence I'll stick to regular steel and aluminum.

I have access to a drill press, but that's about all. I am not a metal worker


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Re: My very late 14 inch f/5 project... new [Re: Benach]
      #3983870 - 08/15/10 06:52 AM Attachment (46 downloads)

Quote:

Can you show a pic from the front, this is not very clear to me.




Maybe the following pic is clearer? It also features the compression spring, and one confusing nut less:


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3984449 - 08/15/10 01:21 PM

Olivier: there is a anodising company nearby here. If you want, we can make an arrangement about that. PM me about that. Anosidising has other advantages as well such as a far better scratch resistance.
Still don't understand the purpose of the blocks.


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Re: My very late 14 inch f/5 project... new [Re: Benach]
      #3984814 - 08/15/10 05:46 PM

Quote:

Olivier: there is a anodising company nearby here. If you want, we can make an arrangement about that. PM me about that. Anosidising has other advantages as well such as a far better scratch resistance.
Still don't understand the purpose of the blocks.




Thank you for your offer. I'll PM you about this.

Which blocks do you mean? Do you mean the collimation setup?


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3985744 - 08/16/10 06:53 AM

I'm now considering using threaded inserts for the collimation. Simpler than adding all this other extra collimation hardware (square tubes).

For the trusses I'll take 25mm or 30mm round aluminum trusses. I can choose between 1.5mm and 2mm wall thickness.

Which would you recommend?

Edited by Olivier Biot (08/16/10 06:58 AM)


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3985804 - 08/16/10 08:01 AM

Olivier: I'd recommend you to redesign your collimation system. I don't see how it's working. I highly recommend you to use a kinematic collimation system. Then you have to align your primary only once and can do the rest of the collimation on the secondary mirror.
A wall thickness of 2mm has a far better stiffness, so I'd go for that 30mm as well.
Threaded inserts (helicoils) are excellent! However, if you intend to use them, insert them after anodising the construction. Most helicoils I know, are made of stainless steel which will ruin the anodising solution.


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Re: My very late 14 inch f/5 project... new [Re: Benach]
      #3985818 - 08/16/10 08:23 AM

Align your primary only once? We all wish! Bumpy roads to dark sky sites are not so forgiving.

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Re: My very late 14 inch f/5 project... new [Re: Mike I. Jones]
      #3985857 - 08/16/10 09:03 AM

Mike: a Kelvin-clamp (cone-vee-flat) is highly shockresistant as you know. Stiffness then only depends on the springs used.

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Re: My very late 14 inch f/5 project... new [Re: Benach]
      #3985880 - 08/16/10 09:25 AM

Benach- How about a drawing of the collimation setup you envision?

allan


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Re: My very late 14 inch f/5 project... new [Re: m. allan noah]
      #3985935 - 08/16/10 09:58 AM

Allan: I don't have a drawing over here, but on this site you can see another kinematic mount.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3985944 - 08/16/10 10:03 AM

Quote:

the weight MUST go down




Hi Olivier,

I think you have at least 48 bolts and nuts that could be replaced with nylon and maybe save about 1/3 kg assuming the bolts are around 30-32mm x 6 or so and my crude calculations are anywhere near correct.

(Thanks for your note on the other forum.)

Gary


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Re: My very late 14 inch f/5 project... new [Re: Gary Fuchs]
      #3985989 - 08/16/10 10:35 AM

Quote:

Quote:

the weight MUST go down




Hi Olivier,

I think you have at least 48 bolts and nuts that could be replaced with nylon and maybe save about 1/3 kg assuming the bolts are around 30-32mm x 6 or so and my crude calculations are anywhere near correct.

(Thanks for your note on the other forum.)

Gary




Thanks Gary

For what it's worth, I entirely disassembled the UTA today, and here are the weight figures:

  • UTA rings: 2 x 400g = 800g
  • Nuts and bolts (56 of each): 320g
  • Aluminum trusses and corners: 850g
  • Spider and diagonal holder: 400g
  • Formica light shield: 500g


Without any focuser or any other extras I already had a bulky 3kg UTA


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3986856 - 08/16/10 07:11 PM Attachment (61 downloads)

Here's a significant update.

First of all, here's a rendition (in perspective) of the OTA on the rocker box:


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3986863 - 08/16/10 07:15 PM Attachment (55 downloads)

As you can see I changed my mind regarding the trusses. I used rectangular section trusses here with a section of 40mm by 20mm, and I have the choice between 1.5mm wall thickness (0.462kg/m) or 2mm wall thickness (0.605kg/m). Given the section I believe 1.5mm wall thickness should be fine.

What is still missing is the collimation system and the ground board. I didn't draw the focuser either .

Here's another view, from the business end (again in perspective):


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3986876 - 08/16/10 07:23 PM Attachment (54 downloads)

As you can see from the image above, I use an "offset spider" (made by Gary Wolanski over 10 years ago). This spider will produce 4 diffraction spikes like a regular spider, as long as I keep the vanes parallel and perpendicular.

Here's a close-up of the secondary holder as seen through the focuser hole:


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3987682 - 08/17/10 04:27 AM

Olivier,

I'd be looking to put the uta on a diet, and reduce the truss count by 2... Both will save weight.

Have fun


Owen


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Re: My very late 14 inch f/5 project... new [Re: Owen]
      #3987690 - 08/17/10 04:42 AM

Quote:

Olivier,

I'd be looking to put the uta on a diet, and reduce the truss count by 2... Both will save weight.




Hi Owen,

Thanks for your recommendations.

If I reduce the truss count from 8 to 6 I can no longer use square section trusses. In that case I'll have to go for 25mm or even 30mm diameter round trusses.

Will the increased forces on the remaining trusses not require a sturdier and heavier mirror box, and more complex truss clamps?

Cheers,

Olivier


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3987711 - 08/17/10 05:41 AM Attachment (55 downloads)

Regarding collimation, Chriske suggested I use push-pull.

Since I plan on collimating the scope from the front, I basically inverted the push-pull setup.

I attached a concept paper drawing to this message, and you'll notice I didn't add a compression spring (yet).

The mirror cell rests on the bottom board, the top board contains the push-pull hardware pointing towards the stars. The top board will be firmly attached to the side of the rocker board (e.g.,with L irons at top and bottom to prevent sagging and play).

The left bolt is the PULL bolt: it regulates the collimation. The bolt to the right is the PUSH bolt: it locks the collimation in place.

The head of the PULL bolt rests on a large washer to avoid imprinting in the top board. The bottom of the PUSH bolt makes contact with the bottom board on a hard surface, e.g. the flat head of a countersunk wood screw.

This setup requires 2 threaded inserts with their top pointing downwards. This way both threaded inserts are pulled into the wood under normal compression load.

What do you think?


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3987740 - 08/17/10 06:40 AM

Hi Olivier,

You would still be able to use a square section, but the geometry of the clamps does get a little more challenging - most incidences that I've seen take the angle from the mirror box, and transpose that on the uta.

The box sections specified are immensely strong as they are, and moving to 6 rather than 8 trusses will triangulate the structure more effectively - so potential is there to reduce the wall thickness further.

Making the mirror box structure a bit more substantial will help overall balance...

Have fun



Owen


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Re: My very late 14 inch f/5 project... new [Re: Owen]
      #3987859 - 08/17/10 08:40 AM Attachment (48 downloads)

I'll give the 6 truss concept a try this afternoon.

Here's an illustration of a push-pull system with compression springs (the collimation bolts do not rotate in a threaded insert - they're fixed to the mirror cell board):


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3987883 - 08/17/10 08:59 AM

Quote:

What do you think?



Read your PM to know what I think


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3987932 - 08/17/10 09:29 AM Attachment (43 downloads)

Here's a rendering with lateral rails in place (4 slanted corner irons). This way I can use smaller diameter setscrews for the push-pull system.

Eventually I may give up entirely the idea of the compression springs in the collimation unit. They're not needed in a true push-pull system. This would further reduce the footprint of my cell


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3988288 - 08/17/10 12:21 PM Attachment (50 downloads)

Here's a first rendering of the OTA with 6 round trusses (30mm diameter, 2mm wall thickness):

Edited by Olivier Biot (08/17/10 12:24 PM)


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3988304 - 08/17/10 12:33 PM

Olivier: I'd go for the 8-truss design. Is stiffer and apart from that: for optimal stiffness, the spider vanes should be mounted between the trusses, seen from above. In your posting of 08/16/10 07:15 they're halfway the trusses.

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Re: My very late 14 inch f/5 project... new [Re: Benach]
      #3989139 - 08/17/10 07:12 PM

Quote:

Olivier: I'd go for the 8-truss design. Is stiffer and apart from that: for optimal stiffness, the spider vanes should be mounted between the trusses, seen from above. In your posting of 08/16/10 07:15 they're halfway the trusses.




The 8 truss design is simpler for a first scope. Especially since I am building it like Russian babushka dolls (UTA cage fits in mirror box fits in rocker box).

I can't choose where to place the spider vanes due to the type of secondary holder.

What I'm more concerned with, is that the current UTA rings (octagons, in fact) are not sufficiently stiff for the job. I can easily bend them out of shape.

Hence, I'll need to have other wood (birch or beech plywood instead of the current Chinese lauan), and most likely wider UTA rings. This means I won't be able to stack the secondary cage inside the mirror box.

Bummer.


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3989974 - 08/18/10 04:55 AM

Olivier: what about rotating the secondary with the whole uppercage? If you look into your eyepiece at 45degr. you can still place the spider between the trusses.

Dunno what kind of profile pieces you intend to use for the UTA, but most of them should be stiff enough as soon as the ring is fully closed.


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Re: My very late 14 inch f/5 project... new [Re: Benach]
      #3990050 - 08/18/10 07:10 AM

I'm not so keen of rotating the focuser 45 since it will be trickier to observe close to zenith then (the rocker and the back of the UTA will be in the way).

Due to the lack of stiffness of my current set of UTA rings (circular cutout in the inside, octagonal at the outside) I'll probably have to make new UTA rings.

I don't know if birch plywood will be stiffer than the lauan I currently have.


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Re: My very late 14 inch f/5 project... new [Re: Benach]
      #3990221 - 08/18/10 09:36 AM

Quote:

Olivier: I'd go for the 8-truss design. Is stiffer and apart from that: for optimal stiffness, the spider vanes should be mounted between the trusses, seen from above. In your posting of 08/16/10 07:15 they're halfway the trusses.




Interesting. I'd always heard that the 6-trusses are stiffer because they're all working. With 8, you only have 4 supporting the weight of the UTA and 4 controlling side to side motion... - j


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Re: My very late 14 inch f/5 project... new [Re: jayscheuerle]
      #3990297 - 08/18/10 10:20 AM

I bet the stiffness also depends on how the trusses are connected. If you leave a couple inches between the truss ends, then you remove part of the stiffness.

The hardware that joins 2 trusses often acts like a truss. Its motion is however constrained by means of tightening nuts and bolts.


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3990541 - 08/18/10 12:11 PM

Olivier: I don't mean rotating the focuser, I meant rotating the entire upper cage.

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Re: My very late 14 inch f/5 project... new [Re: Benach]
      #3990557 - 08/18/10 12:23 PM

If you test the stiffness of the upper cage "rings" by them selves you will get an unrealistic estimate of their stiffness. You want the upper cage as a whole to be stiff and able to support the things attached to it (spiders, focusers, pictures of Lady Gaga etc.).

To maximized the strength without adding more material and parts you'll want to have struts right where the spider attaches so you can bolt to the strut. The focuser may need its' own board to attach to (I used aircraft grade plywood - very very stiff) the rings. This board will also make the cage stiffer.

If you can make the material between the rings part of the structure (e.g. use laminate that is pinched between the rings so you end up with it being the webbing in an I beam type structure) you can make a very light but strong upper cage.

And light!


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Re: My very late 14 inch f/5 project... new [Re: rboe]
      #3990562 - 08/18/10 12:25 PM

Oh, add a small mounting board or truss for a telerad, rigel or finder scope (rigel is smaller and lighter of the three). I added holes for mounting eye pieces in the focuser board. That way I can stay at the scope to swap out eye pieces.

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Re: My very late 14 inch f/5 project... new [Re: Benach]
      #3990574 - 08/18/10 12:31 PM

Quote:

Olivier: I don't mean rotating the focuser, I meant rotating the entire upper cage.




That's what I understood as well

If I do so, then the focuser will also be rotated 45 around the mechanical axis of the OTA. That's not a thing I want to do with this scope since I want to avoid requiring a step ladder while stargazing with it (and falling off it in a moment of less attention)


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Re: My very late 14 inch f/5 project... new [Re: rboe]
      #3990620 - 08/18/10 12:47 PM

Good point(s) Ron.

The original UTA was bolted together, but did not really act as a whole, since there was quite some play.

I have now added a piece of plywood for the focuser board, and I plan on moving the struts where the spider vanes connect to the UTA.

I still have the 1mm thick sheet of formica (melamin resin) that I plan on using as a light shield. If I attach it to the inside of the UTA rings, it will probably add to the stiffness of the UTA.

FWIW this formica sheet has a density of about 1.5kg/dm. With a height of 300mm it weighs around ~0.6kg.

Hmmm... maybe I should use wooden blocks like the focuser board instead of the struts?


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3990722 - 08/18/10 01:29 PM

Metal will have a higher bending limit than wood for that spider so I would steer you towards a single metal part to attach the spiders to.

I inserted my laminate into grooves I routed into the rings. Huge PITA to assemble, take about four hands it seems like, but the cage had this nice "one part" feel to it once done. You can pinch it a fair amount, unlike kydex.

Look for ways to bolt through the ring instead of using the angle brackets you had before. Even gluing in blocks of wood into the ends of the channel for a wood screw to dig into. Or, cut the channel so that the ribs are shorter and top surface is longer (like a tab). This tab can be screwed into the edge of the ring but that is not ideal.

Make the tab longer so it goes around the ring and folds flat on top. Screw through it into the top of the ring and the screw will have superior holding power.

You could also bend it so it was on the bottom of the ring but that makes attaching a bit more difficult.


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Re: My very late 14 inch f/5 project... new [Re: rboe]
      #3990768 - 08/18/10 01:44 PM

Quote:

Metal will have a higher bending limit than wood for that spider so I would steer you towards a single metal part to attach the spiders to.




Do you mean I should go into the direction of a single metal UTA ring?

Quote:

I inserted my laminate into grooves I routed into the rings. Huge PITA to assemble, take about four hands it seems like, but the cage had this nice "one part" feel to it once done. You can pinch it a fair amount, unlike kydex.




In my case that'd require a very thin router bit (1-2mm). Not sure that will be feasible. I'd have to do it with the Dremel.

Quote:

Look for ways to bolt through the ring instead of using the angle brackets you had before. Even gluing in blocks of wood into the ends of the channel for a wood screw to dig into. Or, cut the channel so that the ribs are shorter and top surface is longer (like a tab). This tab can be screwed into the edge of the ring but that is not ideal.

Make the tab longer so it goes around the ring and folds flat on top. Screw through it into the top of the ring and the screw will have superior holding power.

You could also bend it so it was on the bottom of the ring but that makes attaching a bit more difficult.




Do you mean that I should use corner irons with a longer "tab" on which I attach the spider vane? And that this corner iron makes contact on the flat side of the ring as well as on the edge (outer cylindrical surface) of the ring?


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3991359 - 08/18/10 06:18 PM

Quote:

Russian babushka dolls




Matreshka


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Re: My very late 14 inch f/5 project... new [Re: gaidash]
      #3991530 - 08/18/10 07:28 PM

NO, toss those corner irons entirely. Machine the metal trusses you have now to build in the tabs.

I used a 1/8th inch router bit I think. Larger than the thickness but good enough. Used a regular router, no problem. Well, it was a Trend router, they are a bit smaller than your typical woodworking router like your Porter-Cables and DeWalts. Best done before you cut them out.

Still use the double wood rings.


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Re: My very late 14 inch f/5 project... new [Re: rboe]
      #3991595 - 08/18/10 08:03 PM

What do you mean with 'tabs' here? I'm a bit lost

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3991705 - 08/18/10 08:56 PM

Your original channels or struts are C shaped. If you mill off the top and bottom legs of the C you have an I where you milled. That is your tab. I'm thinking you can mill off an 1" and bend that tab in to close off the end of the channel and you now have a tab parallel to the ring that can be used as a mount point.

Mill off more, place the ring on the C part then bend the surplus part of the tab OVER the ring so it captures the ring and use that to fasten to the ring.

This tab can be under or over the ring, just has to be longer if you go over.

Since it is part of the original channel there are no parts to buy, no extra weight to add. Save the screw. Maybe a washer.

I may have to get a napkin and draw you a picture like a real engineer.


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Re: My very late 14 inch f/5 project... new [Re: rboe]
      #3991729 - 08/18/10 09:08 PM

In the original UTA cage the struts were square section aluminum, 20mm x 20mm and 1.5mm thick. They're not "C" shaped.

If I understand it right I'd have to trim off 3 sides of the square section struts at the top and bottom, so that there's a 'tab' protruding. This tab then should go in a routed recess.

Is that what you meant?


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3991958 - 08/18/10 11:23 PM

Shakey memory. Could have sworn they were C channels.

You could make a recess for them, a mortise like you would for a hinge. It would weaken the ring somewhat so I would not do it myself unless I made the ring thicker.


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3991968 - 08/18/10 11:26 PM

Quote:

Without the light shield you can see the structure of the UTA. It's made of 18mm plywood (Lauan?) and held together with 20mm x 20mm square aluminium struts and angle profiles, everything bolted together (no gluing or welding):




Well looky there, square tubes. I did notice that the plies were darn thick on that plywood. It would help a lot if you found some plywood with much thinner plies (which will up your ply count which is always good).

If you can't and you still need to make it that small to nest it then do what Sky Captain did and go with metal.

But not cast iron or bronze.


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Re: My very late 14 inch f/5 project... new [Re: rboe]
      #3991974 - 08/18/10 11:29 PM

Well poo, the picture didn't come through on the quote.

They make spring disc threaded inserts for round tubes, it would save you some trouble if they made them for square tubes too. Have not looked into that. Otherwise, consider going with round tubes.

Square would be stiffer mounts for the spider but a round one should be stiff enough. Lighter too.


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Re: My very late 14 inch f/5 project... new [Re: rboe]
      #3992310 - 08/19/10 06:16 AM

Thanks for your recommendations Ron.

I'll get some other plywood for the scope. I'll try to get birch as it is know for its many plies.

I am still considering 18mm (3/4") thick plywood.

Since I'm going for new wood I have no reason to question the UTA ring diameter anymore. Here are the properties of 4 ring configurations:

  1. Original, 406mm I.D., 446 O.D. octagon (20mm ring width at narrowest point): volume = 0.636dm (1dm = 1 liter) (reference)
  2. Round, 406mm I.D., 446 O.D. (20mm ring width): volume = 0.482dm (-25%)
  3. Round, 406mm I.D., 456 O.D. (25mm ring width): volume = 0.609dm (-5%)
  4. Round, 406mm I.D., 446 O.D. (30mm ring width): volume = 0.740dm (+16%)


This means that I'm having a 5% lighter and stronger UTA ring if I take a 25mm wide round ring section than with my original octagonal section.

Going from 25mm to 30mm will add about an ounce or two.

I think I'll stick to 25mm width for now.


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3992371 - 08/19/10 07:52 AM

Looking great on the pictures, with what software are you working to make those?

Thanks,


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Re: My very late 14 inch f/5 project... new [Re: luukieboy2]
      #3992578 - 08/19/10 10:40 AM

Inventor.

We're spoiled nowadays with 3D solid modeling tools: Inventor, Alibre, Rhino, Sketchup...


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3992901 - 08/19/10 01:30 PM Attachment (58 downloads)

Time to kill the engineer

Here's an overview of the OTA on the rocker box. I moved the altitude axis location further up the mirror box to be more "bottom heavy". Apart from the altitude trunnions there's no mirror box part protruding further towards the UTA.

Here's a final rendering without ground board:


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3992912 - 08/19/10 01:34 PM Attachment (50 downloads)

Here's a detail of the truss connectors I plan to have:

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3992948 - 08/19/10 01:42 PM

I just measured the height of the eyepiece above the bottom of the rocker base: 1650mm. That's a perfect match with what I had in mind: it coincides with the height of my eyes above ground level

The 8 round trusses are around 1000mm long, and have a section of 25mm and a wall thickness of 1.5mm. They will weigh 300 grams each (add some for the L irons), hence 2.5kg for the trusses.


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3993792 - 08/19/10 08:09 PM

I just learned something new today. Apparently beech plywood is also high grade high ply. So it'll either be 11-ply beech or birch.

I will need a full 2.44m x 1.22m board.


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stringscope
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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3994383 - 08/20/10 02:47 AM

Hello Olivier,

have you considered using larger diameter altiude trunions and a balance point some distance above the top of the mirror box? This will also reduce the height of the rocker.

Cheers

Edited by stringscope (08/20/10 05:19 AM)


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Re: My very late 14 inch f/5 project... new [Re: stringscope]
      #3994440 - 08/20/10 04:35 AM

Hi Ian,

I have been considering using larger alt trunnions, but then I was worried about (3) bumping into them, (2) breaking them during transport, and (1) that the scope could end up in such a situation where there is no lateral containment of the OTA in the rocker, increasing the risk of it falling off the rocker while observing.

Right now I believe I'm at the widest I can go. But please feel free to convince me of the contrary


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stringscope
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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3994453 - 08/20/10 04:59 AM Attachment (50 downloads)

Hi Olivier,

here is my 16" F4.5 scope. Altitude trunions are 2X mirror diameter = 800mm. Balance point is 115mm above the top of the mirror box. Works well no aparent flexure, havent bumped into them yet. This is Mk2 version. the Mk1 version had 700mm diameter trunions, worked very well.

Cheers,

Edited by stringscope (08/20/10 05:02 AM)


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stringscope
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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3994454 - 08/20/10 05:00 AM Attachment (62 downloads)

This one probaly better shows the balance point above the mirror box top

Edited by stringscope (08/20/10 05:01 AM)


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Re: My very late 14 inch f/5 project... new [Re: stringscope]
      #3994461 - 08/20/10 05:11 AM

Awesome scope Ian

Very nice craftsmanship

I see your rocker has a larger thickness than the mirror box. Did you bond 2 boards together for the rocker and the altitude trunnions?


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stringscope
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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3994464 - 08/20/10 05:16 AM

Thanks Olivier. I posted a lot of photos on this forum earlier today. Whiffletrees, front collimation etc.

Yes, the rocker sides are built up from 12 and 18mm ply sheets glued together. The altitude bearings are 2 X 18mm ply pieces glued together. This gives me 6mm clearance between the mirror box and rocker per side. The mirror box is made from 12mm ply.

Edited by stringscope (08/20/10 05:17 AM)


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stringscope
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Re: My very late 14 inch f/5 project... new [Re: stringscope]
      #3994466 - 08/20/10 05:21 AM

Olivier, Also note the keepers to prevent the trunious from "derailing" and running off the bearing surfaces.

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Re: My very late 14 inch f/5 project... new [Re: stringscope]
      #3994477 - 08/20/10 05:34 AM

Quote:

Olivier, Also note the keepers to prevent the trunious from "derailing" and running off the bearing surfaces.




I completely overlooked that

Right now I have 2mm inner clearance on each side of the rocker. Allows me putting some low profile felt or PTFE spacers to avoid the mirror box from scraping the rocker.


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3994775 - 08/20/10 09:50 AM

I'm not sure you need those tabs on the side, after all, the mirror box acts as a huge inside tab to prevent lateral movement.

However; from personal experience over travel in scope swing, mainly in going over backwards is a problem and a stop on the bearing to prevent over rotation is a good thing.

Typically it just runs off the teflon pad but is a bit of a pain to get back on. Bad angle and all, but it is doable.

Very nicely built scope there.


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Re: My very late 14 inch f/5 project... new [Re: rboe]
      #3994850 - 08/20/10 10:32 AM

I'm back from the sawmill

I bought one big birch plywood panel (2.50m x 1.25m, 18mm thick, 13 ply), and had them saw it to size. Not very cheap though: 100 EUR for the panel and sawing.

I now have all wood parts I need, apart from the front panel of the rocker. Tonight we should be making noise and tons of sawdust routing the discs and other circular cuts

Let's party


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3996022 - 08/20/10 08:01 PM Attachment (42 downloads)

Time to prove that the construction started.

Trunk of my car loaded with planks and boards:


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3996026 - 08/20/10 08:02 PM Attachment (48 downloads)

Tonight we routed both UTA rings. Chriske brought his router and a circular jig for routing circular cuts. We went through the full thickness in 2 passes.

Here's a shot of the rings after sanding the edges:


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3996031 - 08/20/10 08:03 PM Attachment (46 downloads)

The UTA rings weigh around 410 grams. That's 10% less than the original rings. In addition, the round rings are much stronger.

This is what the UTA may look like (the focuser board is not yet sawn to size, hence it's not on the image). I'm considering using those plywood struts instead of metal trusses connecting both UTA rings. I'll position them where the spider vanes have to be attached. My only worry is whether the plywood won't split if I use screws along the plies.

Edited by Olivier Biot (08/20/10 08:06 PM)


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3996032 - 08/20/10 08:04 PM Attachment (50 downloads)

And with the Formica light shield in place:

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3996208 - 08/20/10 10:28 PM

Very elegant spider design, Olivier. Reminds me of Gary Wolanski's work.

--George


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3996488 - 08/21/10 01:18 AM

Looking nice Olivier. Nice feeling to get started finally i'll bet.

Quote:

My only worry is whether the plywood won't split if I use screws along the plies.





Just pre-drill all the holes and make sure they are centered in the middle of the wood. Drill bit size should be the same diameter as the center solid part of the screw being used.


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Re: My very late 14 inch f/5 project... new [Re: Sky Captain]
      #3996614 - 08/21/10 04:03 AM

On the edge of ply, I also add some white glue into the pilot holes.

Holds the ply together nicely


Owen


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Re: My very late 14 inch f/5 project... new [Re: george golitzin]
      #3996665 - 08/21/10 05:49 AM

Quote:

Very elegant spider design, Olivier. Reminds me of Gary Wolanski's work.

--George




It actually is Gary Wolanski's work!

I bought the secondary holder and offset spider from him at the end of the 90s and then life & work interfered with my telescope building endeavor.


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Re: My very late 14 inch f/5 project... new [Re: Sky Captain]
      #3996666 - 08/21/10 05:50 AM

Quote:

Looking nice Olivier. Nice feeling to get started finally i'll bet.

Quote:

My only worry is whether the plywood won't split if I use screws along the plies.





Just pre-drill all the holes and make sure they are centered in the middle of the wood. Drill bit size should be the same diameter as the center solid part of the screw being used.




Makes perfect sense Kerry! I'll do as you recommend.


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Re: My very late 14 inch f/5 project... new [Re: Owen]
      #3996667 - 08/21/10 05:51 AM

Quote:

On the edge of ply, I also add some white glue into the pilot holes.

Holds the ply together nicely

Owen




So far I never glued the edges of the panels. But this time I see no reason why I shouldn't. It will add to the overall stiffness of the assembly as well


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #3997676 - 08/21/10 05:47 PM

Hi Olivier,

The glue is only supposed to re-enforce the pilot hole for the screw, but screw and glue (along the whole edge of the panel), will be very good - much stronger than just the screws alone

Have fun


Owen


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Re: My very late 14 inch f/5 project... new [Re: Owen]
      #4012750 - 08/29/10 08:16 AM

Thanks for the clarification Owen!

We still need to finish routing the 2 mirror box baffles, the altitude trunnions and the side panels of the rocker box.

One parameter I still have to check, is the minimum clearance between mirror box and rocker box in case I want to add digital encoders. Any opinions here?


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4012890 - 08/29/10 10:26 AM Attachment (55 downloads)

This afternoon I started transposing the 3D CAD drawings to wood. I caught one minor error in my mirror cell in doing so. This error did not affect my bill of materials, fortunately.

Here's the plywood board with a first set of pencil marks for laying out the location of the 3 pivot assemblies, as well as a number of other guides (e.g., for positioning the 45 lateral support hardware):


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4013754 - 08/29/10 06:29 PM Attachment (43 downloads)

In an attempt to optimize the available wood I want to try out routing the side panels of the rocker board and the altitude trunnions from one board. The remainder of that board will serve as front panel for the rocker.

The board has a length of 1250mm and a width of 536mm. The router bit is 10mm wide. In the attached picture I highlighted the router bit width in gray.

I would start making the small horizontal "truncation" cuts (marked in red in the attached picture). Then I will route the circular cuts for the side panels of the rocker box (yellow) until I hit the "truncation cuts". Finally I want to proceed with the altitude trunnion (blue).

The green part will be cut off and will serve as front panel for the rocker box.

Sounds feasible?


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4013794 - 08/29/10 06:50 PM Attachment (46 downloads)

In the following layout I allowed the clearance of the router bit to overlap. This results in 30mm more height for the front of the rocker box. In addition it should create less sawdust.

I could even move the center of the altitude trunnion 5mm further downward. Then I would still be able to move the router more than 20mm further than the red cut line before I hit the altitude trunnion. It would add an extra 10mm to the height of the front panel of the rocker. Maybe that is too extreme an optimization?


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4014406 - 08/30/10 12:12 AM

You made allowances for the kerf of the router bit but not the saw blade for cutting the straight cuts (between the green and yellow pieces). It could be as bad as 3mm or more.

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Re: My very late 14 inch f/5 project... new [Re: rboe]
      #4015922 - 08/30/10 05:55 PM

Correct. The saw blade is much narrower than the router bit. In addition that cut is a straight line, while the round kerfs were more tricky to lay out properly

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4050270 - 09/15/10 05:50 PM

Friday we should be able to finalize routing the missing parts.

Among others, I'd consider routing the focuser hole in a 4" wide focuser board.

Any recommendations on the diameter of this hole for a regular 2" focuser?


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4051358 - 09/16/10 06:58 AM

Quote:

Among others, I'd consider routing the focuser hole in a 4" wide focuser board.

Any recommendations on the diameter of this hole for a regular 2" focuser?




Since I just ordered my focuser (same as Sky Captain's - a 2" low profile dual speed focuser made by Long Perng and sold under various brands), I know what dimensions the focuser board should have. From the documentation by Orion Telescopes I will need to foresee a drawtube hole about 2.5" (63.5mm) in diameter.

I have a 2.5" (64mm) hole saw but I'm considering routing that hole instead of drilling it on the drill press. What would you do?


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4054494 - 09/17/10 01:31 PM

FWIW the documentation seems to be for a similar but different (and flawed) focuser.

The focuser I ordered has been shipped this afternoon, so I hope I'll get it somewhere next week


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4063915 - 09/21/10 03:56 PM

Got the focuser today. It's identical to Sky Captain's. Very beefy construction, looks sturdy and feels good as well.

Now it's a matter of moving forward with the UTA.

Things I'm currently evaluating:

1. get a flat base for the focuser

2. design a filter slide that will ride underneath the focuser


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4066026 - 09/22/10 02:12 PM Attachment (32 downloads)

Here's a shot of the focuser:

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4066034 - 09/22/10 02:15 PM Attachment (36 downloads)

And here's a photo showing 12 kg of aluminum profiles, some of which will make it in my scope (the white stuff under the aluminum is a sheet of self-adhesive Resopal (formica laminate):

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4066574 - 09/22/10 06:26 PM Attachment (33 downloads)

Chriske managed to arrange a gap in his busy schedule to help me out tonight. We have been routing the altitude trunnion disk and the alt bearing cutouts for the rocker box side panels.

Tonight's work consists of altitude trunnion disk (left) and 2 rocker box side panels (right). The tallest has to be shortened to be the exact size of the shortest:


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4066581 - 09/22/10 06:28 PM Attachment (43 downloads)

And here's a shot showing the altitude trunnion disk sitting in the rocker box side panel cutout:

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4070393 - 09/24/10 01:34 PM Attachment (37 downloads)

I'm fortunate to have a home improvement store around the corner where you can have own wood cut for a small fee.

Hence I asked them to cut the side panels of the rocker to dimension. The leftover of the longer side panel was then trimmed to become the front panel of the rocker.

Here's a photo of the not yet assembled rocker:


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4072995 - 09/25/10 06:01 PM Attachment (35 downloads)

Making the focuser board. After penciling where the focuser drawtube hole should be, I mounted the 64mm hole saw to my power drill, and then placed the power drill in a mobile drill stand.

This drill stand helps in positioning the drill, and in keeping the drill square to the focuser board.

Here I'm past the middle of the full focuser board thickness:


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4073017 - 09/25/10 06:15 PM Attachment (31 downloads)

Time to flip the focuser board for drilling the opposite side. Here it's a matter of carefully aim the centering bit in the existing hole:

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4073019 - 09/25/10 06:16 PM Attachment (33 downloads)

The hole saw nicely cuts through the birch plywood. I don't do it in 1 time to avoid rip-out (typical with most if not all hole saws).

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4073022 - 09/25/10 06:16 PM Attachment (30 downloads)

The rough edges of the hole are smoothed with a Dremel and drum sander. I used a worn out sander to avoid removing excess wood. Then I finished with #120 and #400 sandpaper.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4073027 - 09/25/10 06:17 PM Attachment (36 downloads)

Here the focuser board can be seen, cut to length (264mm).

I still have to see what I will do with the small voids at the visible edges of the plywood.


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4073029 - 09/25/10 06:18 PM Attachment (30 downloads)

Time to assemble the rocker. I use inexpensive miter corner clamps (red and blue) for keeping the side panel and the bottom of the rocker square during initial assembly.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4073031 - 09/25/10 06:19 PM Attachment (39 downloads)

I pre-drill the holes about 50% of the 60mm screw length to avoid splitting with a drill bit as wide as the "stem" (kernel) of the screw. I also use a countersink bit (on photo) to make sure the screw holes don't protrude.

This is the bottom of the rocker. It will eventually be covered with a sheet of formica laminate.


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4073034 - 09/25/10 06:20 PM Attachment (32 downloads)

Attaching one of the side panels of the rocker to the bottom plate.

I now know I should first assemble the "box" of the rocker, and then attach this "box" to the bottom board. This would avoid a 1mm play at one joint (I could then spread this evenly across all sides).


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4073036 - 09/25/10 06:21 PM Attachment (32 downloads)

For pre-drilling the screw holes I also use the mobile drill stand. This way I ensure the screw will go square to the board, and not ruin the plywood instead.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4073037 - 09/25/10 06:21 PM Attachment (31 downloads)

Rocker fully assembled, as viewed from the "back" (the rear panel is lower since the bottom of the OTA needs to swing above it).

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4073039 - 09/25/10 06:22 PM Attachment (33 downloads)

Side view of the rocker. The front (right) is held by 5 screws to the ground board and 3 screws to each side panel. The rear (left) is held by 5 screws to the ground board and 1 screw to each side panel.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4073569 - 09/25/10 11:50 PM

The thing I like about your post is how you use basic power tools. I have so many tools that make the job easier but not really needed. Very good work.

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Re: My very late 14 inch f/5 project... new [Re: kb4mxo]
      #4073857 - 09/26/10 05:35 AM

Thanks

I know my limitations, hence I stay at using tools I master. In addition I have no machine shop or shed where I can do this sort of things, hence everything happened in my kitchen (which I have to thoroughly clean now )

Eventually I'd like to get a good plunge router so I don't have to ask all the time somebody else to do it for me (and in addition I could do somebody else the favor of routing disks and circular openings ).


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4073913 - 09/26/10 07:12 AM

Olivier,
Are you using wood glue as well or just the screws?

Rob


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Re: My very late 14 inch f/5 project... new [Re: NHRob]
      #4073931 - 09/26/10 07:33 AM

Quote:

Olivier,
Are you using wood glue as well or just the screws?

Rob




Right now I'm only using wood screws (4.5mm x 60mm) spaced at 100mm intervals. That's 30 wood screws so far for the rocker alone.

During final assembly I want to use some wood glue in all butt joints.


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4073937 - 09/26/10 07:44 AM Attachment (29 downloads)

The focuser mounting plate resting on the focuser board (perspective view). The plywood is 18mm thick 13-ply birch, 100mm wide. The aluminum focuser base plate is about 105mm x 105mm, the feet are 10mm high and there's 80mm clearance between both feet.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4073939 - 09/26/10 07:45 AM Attachment (27 downloads)

Lateral view from top/bottom. The 2 holes hold recessed retaining screws that attach the body of the focuser to the base plate. There are 4 of these in total.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4073940 - 09/26/10 07:46 AM Attachment (33 downloads)

The shaft of the fully racked in focuser protrudes about 17mm from below the flat bottom of the focuser (which coincides with the bottom of the focuser mounting plate).

The "feet" of the focuser mounting plate are 10mm tall and 80mm apart.

So, if I decide on flushing the bottom of the focuser with the plywood focuser board, then I still have 1mm clearance for the bottom of the focuser tube (18mm plywood - 17mm fully racked-in depth).

Another option is to use the current clearance (11mm = 18mm plywood + 10mm "feet" - 17mm max depth of fully racked-in focuser) for adding a filter slide underneath the focuser...

Edited by Olivier Biot (09/26/10 07:59 AM)


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4102933 - 10/09/10 08:35 AM Attachment (36 downloads)

Preparing to cut one of the three 150mm long sections of 30mm x 30mm x 30mm x 3mm square U section aluminum profiles. A tea light candle serves for lubricating the saw blade while cutting the aluminum.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4102935 - 10/09/10 08:36 AM Attachment (34 downloads)

Cutting one of the three 150mm long sections of 30mm x 30mm x 30mm x 3mm square U section aluminum profiles. The toughest part is the bottom where I have to cut through the 30mm wide, 3mm thick bottom section of the U profile.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4102939 - 10/09/10 08:37 AM Attachment (33 downloads)

This photo shows the 3 U square sections in place on the mirror cell collimation board. The ends of the cut sections have all been filed with a fine *BLEEP* file and then sanded with #400 sandpaper.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4102943 - 10/09/10 08:37 AM Attachment (36 downloads)

Preparing to cut one of the three 130mm long section of 20mm x 20mm x 2mm square aluminum tube that will be used for one of the 3 mirror cell pivots. These will come in the square section U profiles.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4102946 - 10/09/10 08:39 AM Attachment (37 downloads)

The aluminum profile sections for the 3 pivots of the mirror cell positioned on the collimation board.

Now I have to drill these profile sections for the pivot hardware (bolt + PTFE bushing) and for securing the pivots in place on the collimation board (a couple wood screws)


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4103453 - 10/09/10 02:02 PM Attachment (34 downloads)

Tonight I did some more woodworking: cut the altitude bearings from the big routed disk.

Tools involved: hacksaw, sandpaper, Dremel Trio (with the rotary drum sander).

I was surprised how easy it is to make a straight cut with a hacksaw and a plywood straight edge:


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4103458 - 10/09/10 02:04 PM Attachment (37 downloads)

As can be seen in this photo, I have a near perfect cut, maybe off by ~.5mm. That should be easy to trim.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4103460 - 10/09/10 02:07 PM Attachment (32 downloads)

The cut has been "straightened" with a rotary drum sander mounted on the Dremel Trio guided against a straight piece of plywood. Then I sanded the cleaned entire straight cut, first with coarse paper then with fine paper. Finally I slightly bevelled the edges of the plywood to avoid chipping.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4103469 - 10/09/10 02:15 PM

it progresses .....

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Re: My very late 14 inch f/5 project... new [Re: Víctor Martínez]
      #4103840 - 10/09/10 04:49 PM Attachment (35 downloads)

Yes Vctor

And even more now. The formica laminate edging has been cut to the correct size (+2-3mm) by scoring it 4-5 times with a sharp utility knife, and then carefully lifting the excess while keeping the metal guide for making the cut above the edging:


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4103847 - 10/09/10 04:52 PM Attachment (39 downloads)

Gluing the formica laminate edging to the side of the altitude bearings, with urethane glue (water proof for Belgian moist observing sessions... like tonight ).
  • First I put some scrap wood with spacers under the straight edge of the altitude trunnion.
  • Then I secured the sides with more scrap wood and a J clamp (middle).
  • Then I secured this "unit" with another J clamp to the top of the work mate (you can see it at the far right).
  • Then I cleaned the edge and moisturized it a bit with water on a cloth.
  • Then I cautiously applied the urethane glue as a narrow strip of glue in the middle.
  • I then used a piece of scrap wood to evenly spread the glue on the side of the altitude trunnion.
  • Then I carefully positioned the Formica laminate edging on top of the glued edge of the altitude trunnion. I moved the laminate 1" back and forth a couple times to make sure the glue would contact the laminate everywhere.
  • Then I pressed the laminate to the side of the altitude trunnion, and applied a nylon belt fastener all around, to exert homogeneous pressure.
  • I increased the pressure by adding some scrap wood between the belt and the bottom of the work mate (you can see such protruding piece of wood to the far right).
  • I removed glue stains with acetone, which was rather easy.

FWIW this shot shows the "inner" side of the altitude trunnions (that will be mated to the primary cage).


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4103851 - 10/09/10 04:53 PM Attachment (33 downloads)

This is the "outer" view of the altitude trunnions (the side exposed to the observer).

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4103854 - 10/09/10 04:54 PM Attachment (37 downloads)

In this shot you can see how I positioned the altitude trunnion on the work mate.

Since the laminate edging was cut a bit longer than needed, I added some scrap wood under the straight side of the altitude trunnion. To ensure that no glue spill would attach this scrap wood to the altitude trunnion, I used 2 wooden spacers (yellow) between the scrap wood (bottom) and the altitude trunnion.

You can also see the scrap wood added between the belt fastener and the bottom of the work mate to increase the pressure on the glued edges.


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4104045 - 10/09/10 06:21 PM

According to the info on the glue bottle this urethane glue sets in 3 hours. I still see no major catastrophe yet. Keeping fingers and toes crossed for the time being

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4104805 - 10/10/10 05:08 AM

If I ride this racket to my wife in the kitchen of the house, she kill me

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Re: My very late 14 inch f/5 project... new [Re: Víctor Martínez]
      #4104835 - 10/10/10 05:56 AM

I have no workshop or machine shop at home, and I live alone in my condo

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4104840 - 10/10/10 06:01 AM Attachment (37 downloads)

As I posted in the laminate thread, I tried trimming the excess formica laminate edging with a Japanese-style flexible saw. This went OK for the first 30% but soon the saw started chipping off bits of laminate at the cut.

In addition I noticed that some places had no glue. How this could have happened is a mystery to me, but anyway. The places where this occurred made the saw "sing". At 2 places a tear was produced.

I have a couple options now: leave it be, apply a 2nd layer of laminate (and have someone trim it for me with the proper tools), remove the laminate and redo.

Here's a photo of the worse portion:


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4105526 - 10/10/10 02:26 PM

If that's the worst part, I certainly wouldn't re-do it. I think if you glue down the torn part it will be fine. You can put that bearing on the side opposite the focuser, where it will seldom be seen. The bearings are also going to be facing the ground and rocker, so their surfaces won't be seen often, not to mention it will be used in the dark most of the time. If you really wanted to touch them up, you could make a paste of dust from the formica surface and some glue, and fill the tiny voids.

Good luck,
Don


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Re: My very late 14 inch f/5 project... new [Re: Don H]
      #4105629 - 10/10/10 03:24 PM

Thanks for your input. I glued the biggest tear in place with some cyanoacrylate gel cement. The smallest one eventually chipped off. It's no drama.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4108162 - 10/11/10 05:00 PM Attachment (32 downloads)

Tonight I punched the holes in the aluminum parts for my mirror cell pivot assemblies.

First I make a black spot close to the place where the punch needs to go with a permanent marker. Then I scratch that black spot to define the point where I need to apply the punch mark for further drilling. Finally I center the punch on the marks and hit the punch with a hammer.

The photo below shows the scratch marks on the dark spot, along with the punch:


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4108166 - 10/11/10 05:02 PM Attachment (43 downloads)

The 3 pivots are marked and punched now:

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4108178 - 10/11/10 05:05 PM Attachment (34 downloads)

The 3 pivots will sit in U profiles. They underwent the same procedure.

The punch marks on the square section tubes (pivots) and the punch marks on the square U sections (pivot holders) are set such that the top of the pivots will coincide with the top of the pivot holders.


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4110744 - 10/12/10 05:07 PM

Hmmmm... I can't source hollow PTFE rods locally unless I have a VAT number (i.e., unless I run a business). I counted on finding them for finalizing my mirror cell.

Anybody knows where I could get 10mm outer diameter, 6mm inner diameter PTFE rod? I only need 3 pieces of 24mm length each.

Ideally also PTFE washers with a bore diameter of 10mm, 2mm thick (6 in total).


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4119534 - 10/16/10 05:59 AM

The mirror cell will have to wait till next Friday. There's maybe an option in which I need neither bearings nor PTFE bushings. Stay tuned

This morning I sanded all sides and edges of the rocker with #180 grit paper mounted on a manual sanding block. I vacuumed most of the sawdust, wiped the remainder off with a paper tissue, and now I'm letting the wind finish the job.

Then I'll apply the 1st coat of marine varnish. Since this will be the first coat I have been advised to add some white spirit to the first coat of the varnish to properly seal the wood.

I have to wait 24 hours between coats. Prior to applying the next coat the varnish must be slightly sanded as well (following the grain of the wood). I got myself some #400 sanding paper for that purpose.


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4120327 - 10/16/10 06:36 PM Attachment (35 downloads)

After sanding and vacuuming the rocker, I also dusted it with a brush and the vacuum cleaner in the immediate vicinity.

Then it was time to apply the marine varnish. The first coat was thinned with ~10% white spirit (recommended on bare wood). I applied the varnish with a 'mohair' varnish roller. First I did the inner sides of the rocker, then the outer sides, and when those dried I did the bottom.

The picture below shows the rocker right after I applied the first coat of varnish to the bottom (top - glossy in this shot).


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4120330 - 10/16/10 06:37 PM Attachment (26 downloads)

Here's a shot with flash of the inner portions of the rocker after having received the 1st coat of marine varnish 5 hours ago:

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4120332 - 10/16/10 06:38 PM Attachment (30 downloads)

Some other wooden parts with the bare wood in the middle for comparison:

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4121248 - 10/17/10 05:18 AM

Nice work!
It's getting shape with every post
It should be a beauty in the end. I can't wait to see the result


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Re: My very late 14 inch f/5 project... new [Re: neo]
      #4121303 - 10/17/10 06:25 AM Attachment (29 downloads)

Thank you Alex

The marine varnish cured well over night, apart from the bottom of the rocker where it was still wet this morning. I now ventilate the room where the rocker sits, and it appears to help curing the varnish.

There are some spots where a couple drops appeared. I'll have to scrape them off with a sharp X-acto knife blade.

Here's a first shot of the rocker with most of the 1st coat of marine varnish cured:


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4121304 - 10/17/10 06:25 AM Attachment (30 downloads)

Another view:

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4121415 - 10/17/10 08:26 AM

If you want a mirror finsh you'll probably need to sand it with a very fine glasspaper and recoate it. By doing so 3-4 times you could end up with an exquisite surface like the high quality furniture

P.S. Oh silly me ...you're probably doing this right now


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Re: My very late 14 inch f/5 project... new [Re: neo]
      #4121422 - 10/17/10 08:34 AM

Yes, that's the plan

I bought special fine varnish grade sanding paper to sand individual coats of varnish in between 2 applications. The idea is to have a very smooth and durable finish.

I am doing this now for the assembled rocker, but I am considering doing this for the individual boards of the remainder of the construction (UTA, primary cage) before assembly. That should maybe speed up part of my work.


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4121849 - 10/17/10 12:32 PM Attachment (31 downloads)

This afternoon I have been computing the dimensions of an optimal 3 curved vane spider: Re: Curved spider: 3 or 4 vanes? (Post #4121326 and following)

Then I sanded the rocker in preparing it to get its 2nd coat of varnish. I also applied the 1st coat of varnish to other parts of the scope (UTA rings, UTA struts...).

Here's a shot of the rocker right after it got its 2nd coat of varnish (this time not thinned with white spirit):


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4121854 - 10/17/10 12:33 PM Attachment (34 downloads)

One of the UTA rings and one of the altitude bearings:

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4121861 - 10/17/10 12:35 PM Attachment (30 downloads)

The focuser board already received its 2nd coat of varnish, as well as 2 of the 4 beams in this shot:

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4123507 - 10/18/10 03:13 AM Attachment (24 downloads)

Time for a coffee break update

The marine varnish cured quite sell overnight. It is easy to distinguish the surfaces that had only 1 initial coat of varnish from the others due to the richer texture of the varnish after 2 coats.

Here's a shot of the rocker this morning. A couple drops formed while curing, but it's no catastrophe. Also, where 2 faces meet inside the rocker there are still some places where the varnish did not cure.


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4123508 - 10/18/10 03:13 AM Attachment (26 downloads)

Another view of the rocker:

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4123510 - 10/18/10 03:14 AM Attachment (31 downloads)

One altitude trunnion, one UTA ring and the focuser board. The latter already received 2 coats of varnish:

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4123511 - 10/18/10 03:15 AM Attachment (24 downloads)

Here's a view on the still wet varnish in the butt joints of the rocker:

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4124591 - 10/18/10 02:55 PM Attachment (27 downloads)

Here's a shot of the rocker in the afternoon sunlight:

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4124596 - 10/18/10 02:59 PM Attachment (35 downloads)

Tonight I experimented with my newly acquired Dremel Trio. It managed to cut through the 18mm plywood at once. Here it sits on the top of the mirror cell board, while cutting one side of the square hole that will hold my 120mm x 120mm box fan.

Note that I put a straight edge as a guide to the LEFT of the Dremel Trio. This way the rotation of the cutting bit naturally pushes the Dremel Trio against the guide.


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4124597 - 10/18/10 03:00 PM Attachment (27 downloads)

Looks pretty straight, doesn't it?

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4124599 - 10/18/10 03:00 PM Attachment (33 downloads)

Here's a view of the same cut from the bottom (which already received 2 coats of varnish):

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4124611 - 10/18/10 03:04 PM Attachment (30 downloads)

In this shot I just finished the 3rd cut. First I did both parallel cuts left and right, then I did the bottom cut.

If you look closely you'll notice that this cut is not as straight as the previous cuts. Reason for this, is that I wanted to check whether the placement of the straight edge was important for the Dremel Trio. Apparently it is, as I had to fight keeping the Dremel from wandering away.

Eventually I did another cut in the other direction to remove most of the unevenness. Some sanding and this cut's "mishap" was history.


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4124614 - 10/18/10 03:06 PM Attachment (29 downloads)

I clamped not only the mirror cell board to the work mate, but also the piece of wood that I was going to cut away. If you don't do so, you'll end up with big splinters and maybe a broken bit.

Before the cut:


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4124617 - 10/18/10 03:07 PM Attachment (31 downloads)

Once the cut was finished, I used a fine wood file on the edges, then I used coarse sandpaper, and finally fine #180 sandpaper on the cut. It's very smooth now:

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4124619 - 10/18/10 03:08 PM Attachment (32 downloads)

The bottom of the mirror cell board, with the box fan installed:

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4124621 - 10/18/10 03:09 PM Attachment (37 downloads)

If the box fan sits flush with the bottom of the mirror cell board, then it protrudes 7mm above the top of the mirror cell board.

Visually:


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4124891 - 10/18/10 04:59 PM Attachment (27 downloads)

This is how I plan to mount the box fan in the mirror cell board. The rubber feet serve as shock absorbers.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4124893 - 10/18/10 05:01 PM Attachment (28 downloads)

And here's a view from the other side of the mirror cell board.

In this shot you can see both hardware alternatives I am considering now for attaching the box fan to the mirror cell board.

At the top I am using wood beams that can sit flush against the pivot U profiles.

At the bottom I am using aluminum stock (here recycled L profiles) sitting flush against the bottom pivot profile. Between the aluminum L profile and the top of the fan corner I'd squeeze in the rubber ring from the previous photo.


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4128473 - 10/19/10 11:22 PM

Woke up early today.

And I see that a couple small insects are sticking to the last coat of varnish I applied yesterday night.

I'll have to sand and reapply a thin coat of varnish.


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4130107 - 10/20/10 04:51 PM

I didn't play with varnish today, however I built a plywood "spacer" to fill the void under the focuser base (it's not simple to find a flat base for my focuser, and I want to add a filter wheel under the focuser anyway ).

Again, the Dremel Trio was used to cut the spacer to size from the cutaway I made in the mirror cell board for the box fan.

I drilled the focuser hole in the spacer the same way as documented earlier up in the thread for the hole in the focuser board.

Here are some shots:







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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4135347 - 10/22/10 09:02 PM Attachment (27 downloads)

Tonight I have been working on the mirror cell. It is almost ready now. The pivot axes are made of 6mm diameter "stub steel", and the aluminum pivot elements have been drilled, first the top side with a 3.5mm drill, then the entire profile with 5.8mm drill. Then a reamer was used to create a hole diameter of exactly 6mm. There's less than 0.1 mm play

The space between the inner pivot and the outer square U profile will be filled with spacers made from a stack of 0.5mm thick PTFE (teflon) washers.

Here's a top view of the cell:


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4135348 - 10/22/10 09:04 PM Attachment (21 downloads)

The fan is attached to the mirror cell board with 4 Z-shaped irons. They were bent from straight in a vise. The M4x40 bolts secure the fan and a safety grid to the 4 Z-shaped irons.

Here's a "perspective view":


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4135355 - 10/22/10 09:07 PM Attachment (24 downloads)

And here's a view with the fan and grid installed at the back of the mirror cell board:

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4135848 - 10/23/10 07:13 AM

I plan on applying self-adhesive felt pads to the pivot beams for supporting the mirror in the cell.

I have still to build the push-pull collimation system and add the lateral support for the primary (2 points at 45 supporting the side of the primary in the plane of the COG).


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4136313 - 10/23/10 12:49 PM

Looks very, very good, Olivier!

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Re: My very late 14 inch f/5 project... new [Re: seryddwr]
      #4136997 - 10/23/10 06:20 PM Attachment (26 downloads)

Thanks Greg

Some more progress pictures.

The bottom of the rocker now has the sheet of self adhesive formica laminate attached, and the edges have been trimmed to size.

In order to do so, the only approach that has proven to work, is scoring it 50-60 times with a sharp box cutter blade along a straight aluminum ruler securely kept in place until the formica laminate was almost entirely cut. I used a T profile kept in place with a long piece of scrap plywood and my foot.

Then I used a medium metal file (I will be bleeped if I use the correct name) to file off the remaining 1mm and to chamfer (bevel) the edge. Then I sanded the edge with #60 grit sandpaper and finally I did a quick pass with #180 grit. I also chamfered the 4 corners to avoid obvious future accidents.


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4137001 - 10/23/10 06:21 PM Attachment (25 downloads)

This is an example of how the UTA might look like. I'm still hesitating about the final number of struts between both UTA rings.

Most likely I'll keep the focuser board and 4 struts at 45 to attach the spider vanes.


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4137006 - 10/23/10 06:22 PM Attachment (26 downloads)

This is where I more or less plan to place the wood screws along the mirror box side panels. I measured everything and marked the holes on a pencil line representing the heart plane of the underlying plywood panel.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4137009 - 10/23/10 06:23 PM Attachment (42 downloads)

The primary cage before assembly as seen from the back. To make sure the front is level, the 4 side panels of the primary cage rest on a piece of plywood. To keep the panels squared I placed one of the future baffle boards at the bottom (the actual top of the mirror box). All 4 side panels touch the sides of that board.

The 4 side panels are kept in place by mean of a tension belt (invisible in this shot).


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4137013 - 10/23/10 06:24 PM Attachment (35 downloads)

To preserve squareness of the sides of the mirror box (primary cage), I placed one of the future uncut square section baffles to the bottom (the actual front of the primary cage).

To preserve the distance between the shorter sides of the primary cage, I use the 2nd uncut baffle vertically (right), and shimmed it with some folded paper.


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4137021 - 10/23/10 06:26 PM Attachment (28 downloads)

The screw holes in the sides of the primary cage (mirror box) have been marked and pre-drilled with a 3mm wood bit (the diameter of the stem of the wood screws I'll be using). To ensure the holes are squared to the side of the panel (and the screws are not drifting outside the plywood) I use a portable drill stand.

To speed up drilling I clamped both panels together after having lined them up. One of the clamps can be seen at the top left.


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4137027 - 10/23/10 06:26 PM Attachment (26 downloads)

The pre-drilled holes in the mirror box side panels have been countersunk. The diameter of the countersunk hole is frequently checked with the head of one of the screws I'll be using.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4137030 - 10/23/10 06:27 PM Attachment (30 downloads)

One of the sides of the mirror box, which is turned upside down in this photo. All 10 screws are in place for this side, so it's time to turn the mirror box around to do the other half. The tension belt keeping the panels together is seen in this photo.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4137032 - 10/23/10 06:28 PM Attachment (34 downloads)

The mirror box with the mirror cell board temporarily attached in place with the help of a small paper spacer.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4137036 - 10/23/10 06:30 PM

I now have to route the primary cage baffles. One baffle will stay close to the primary mirror, the other baffle will be placed at the top of the primary cage. It will be movable to allow the secondary cage to be seated in the primary cage.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4141405 - 10/25/10 04:03 PM

No photos for now, but here's the progress since I last posted:

1. The 3 mirror cell pivots are assembled. It was quite an endeavor to place the stacks of 3 PTFE washers between the U profile and the square pivot. Philately tweezers did the job.

2. The front of the mirror cell board has been done with 2 coats of marine varnish to seal the wood.

3. I did the two mirror box baffles. First I drilled a pilot hole in the middle of the baffle panels. I had to re-drill the holes 3 times (and fill the holes with wood putty) to have then dead center. Then I used my Dremel Trio with a cutting bit and a custom circle routing jig to cut the baffles within 1mm tolerance. Once the cutting done I placed the baffle on a custom centering jig to route the baffle dead center to the right size. This had to be done in 2 passes since the router bits are not as tall as the plywood thickness I'm using (18mm). Then I sanded the routed edges.

4. The corners at the back of the mirror box have also been trimmed. This was also done with the help of the Dremel Trio and a straight piece of plywood serving as a guide, clamped to the panels. The cut off corners will be used to close the bottom of the mirror box at the slanted edges, by attaching a thin plywood board to them.

5. The mirror box and the front mirror box baffle received their 1st coat of marine varnish.

The inside of the mirror box, the inner baffle (sitting right in front of the primary mirror) and the back of the front baffle will not be coated with varnish, but will be painted flat black instead.


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4143735 - 10/26/10 05:03 PM

Tonight I just applied a new coat of varnish on lots of woodwork, including the mirror box.

In doing so I first applied some varnish with a roller, then I 'tipped' the varnish with a varnish brush. The result is outstanding! I can't see any dripping varnish now.

Let's see tomorrow how the varnish cured


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4146406 - 10/27/10 05:59 PM

I can confirm now that tipping the varnish is apparently the way to go. I now applied yet another coat of varnish to 20+ parts, including the mirror box, assorted UTA parts, the mirror cell board and the front of the top baffle.

I'm starting to feel high with the thinner evaporating from the varnish


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4148858 - 10/28/10 06:37 PM

Tonight I drilled the holes in the UTA struts that will hold the 6mm wooden dowels in place. Next is to drill the UTA rings at the right places. I'll have to build a temp frame to hold everything in place. Also I'll have to trim the 4 struts and the focuser board to size as they're up to 1mm off in size now.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4153034 - 10/30/10 06:18 PM

The UTA is almost complete now. The UTA rings have been drilled for the dowels, and the lower ring has the struts in place already. I used glue and dowels for cosmetic reasons: no apparent screw holes

The focuser board bears some more trouble since I want to embed a 2" filter wheel into it. Makes placement of wooden dowels a bot tricky due to little room

I also painted the inner mirror box baffle with flat black spray-on paint. Tomorrow I'll do the bottom.


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4155813 - 11/01/10 07:50 AM Attachment (33 downloads)

I'll post the "making of" images later, but here's a view from the completed UTA with yet another coat of marine varnish. I still need to get some UNC 8-32 x 1 inch SS button allen head bolts to attach the 4 offset spider vanes to the UTA struts (I already drilled the holes), and I need to decide on the UTA truss clamping hardware.

Note also that the focuser board has a small block glued on to accommodate the focuser base. Also, the back of the focuser board has a recess for a future 2" filter wheel.


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4155817 - 11/01/10 07:53 AM Attachment (32 downloads)

Here's a view of the back of the focuser board. I routed a circular channel with my Dremel trio and then completed the work with a wood chisel. Filing and sanding did the remainder of the clean-up.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4156956 - 11/01/10 06:49 PM Attachment (25 downloads)

Some more pics as promised

The 3 mirror cell pivots are now fully assembled. Some cyanoacrylate glue keeps the axis from the pivots in place. Between both aluminum profiles a stack of 3 PTFE washers act as spacers.


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4156960 - 11/01/10 06:49 PM Attachment (30 downloads)

The mirror box has 2 baffles. The circular hole has been cut from 18mm birch plywood with the Dremel Trio. The central hole had to be re-drilled 3 times to get it sufficiently close to the middle of the board.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4156962 - 11/01/10 06:51 PM Attachment (25 downloads)

As you can see in this photo, the cutting bit goes through the 18mm plywood at once. I chose to mount the router this way so the outer edge is clean.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4156970 - 11/01/10 06:52 PM Attachment (29 downloads)

The 4 UTA struts are attached to the UTA rings via dowels. To correctly place the drill holes for the dowels, I created a template (right) in which I placed 2 dowel pins. A slight hit with the hammer imprints the center points of the hoes I need to drill for the dowels. The top beam acts as a guide, and the template is clamped in place after having accurately set its position. Worked like a charm.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4156971 - 11/01/10 06:53 PM Attachment (33 downloads)

Assorted parts after having received yet another coat of marine varnish:

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4156976 - 11/01/10 06:56 PM Attachment (29 downloads)

The mirror box right after applying a coat of marine varnish. Note the slanted sides. They were done with the Dremel Trio and a straight edge.

The cut-out triangles will have 2 functions: guiding the mirror cell board, and as a support for the panels at the slanted side. The triangles will sit a bit "higher" in order to have the small panels come flush with the back of the mirror box.

To evenly spread the coat of varnish, I first apply a coat of varnish with a roller, and then I "tip" the coat with a varnish brush having a teeny little bit of varnish on it.


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4156978 - 11/01/10 06:57 PM Attachment (40 downloads)

The position of the UTA struts on the UTA rings has been measured many times. Once the position was correctly determined (partly thanks to the paper template you can see in the middle) I used scrap wood as guides for positioning the UTA struts. There are dowel pins in the (numbered) strut face and on the UTA ring. Once the UTA strut is positioned where it should go, the strut is checked for squareness and then a couple taps with a rubber mallet imprint the dowel pins in the UTA ring. Then it's a matter of drilling the dowel hole at the correct depth.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4156980 - 11/01/10 06:58 PM Attachment (31 downloads)

I always check everything for squareness while drilling and assembling the UTA.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4156984 - 11/01/10 06:59 PM Attachment (31 downloads)

Determining the placement of the UTA struts on the UTA rings is a very lengthy job. Measuring and triple-checking all the time, and some scrap wood serving as guides.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4156990 - 11/01/10 07:00 PM Attachment (28 downloads)

Before gluing the UTA struts to the UTA rings, the position and squareness of each strut is checked constantly. Scrap wood acts as guides for correctly placing the UTA struts on the UTA rings.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4156993 - 11/01/10 07:02 PM Attachment (34 downloads)

The portable drill stand ensures that the dowel holes are squared. The drill has a bolt-on depth stop. The dowel pins imprinted the center point of the drill bit for the dowel holes on the UTA ring.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4156996 - 11/01/10 07:03 PM Attachment (29 downloads)

Ready to drill hole #2:

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4156999 - 11/01/10 07:04 PM Attachment (30 downloads)

The bottom UTA ring has been drilled for the 1st UTA strut. The assembly will be glued, hence I'll sand away the varnish where I want a good glue contact.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4157003 - 11/01/10 07:04 PM Attachment (31 downloads)

Applying glue to the dowel holes and one face of the first UTA strut. Prior to assembly I sanded the "1" away from the UTA ring.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4157005 - 11/01/10 07:05 PM Attachment (27 downloads)

Once the bottom of the UTA ring got all the struts, it's time to flip over that assembly and start placing it on the other UTA ring. Lots of scrap wood are being used here to position spacers and the likes.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4157007 - 11/01/10 07:06 PM Attachment (29 downloads)

Another view of the setup for placing the bottom of the UTA with the attached UTA struts on the top ring.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4157012 - 11/01/10 07:07 PM Attachment (34 downloads)

The Dremel Trio is used as a router for cutting a circular channel in the back of the focuser board. This channel represents the outer edge of a 2" filter wheel. The part "inside" the channel will be chiseled away.

This photo also shows the 4 dowels in place. The router will trim part of the dowels.


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4157015 - 11/01/10 07:08 PM Attachment (36 downloads)

The back of the focuser board is now ready to get a filter wheel. The plywood was carefully delaminated at one of the plies. The raw surface was then evened out with a coarse file, then with rough sandpaper, and finally with fine sandpaper. The central 3mm hole will be the pivot of the filter wheel, while both holes left and right of this pivot hole are holes from the wood screws that secure the focuser base to the focuser board. I bought shorter screws

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4157017 - 11/01/10 07:10 PM Attachment (34 downloads)

Placing the focuser board on the UTA ring was a piece of cake thanks to 2 identical pieces of scrap wood that together were precisely the width between UTA struts at 45.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4157018 - 11/01/10 07:11 PM Attachment (37 downloads)

The completed UTA woodworking after having applied a coat of marine varnish to it assembled. Notice the recess in the focuser board, and the holes in the UTA trusses for the Gary Wolanski offset spider. Below the UTA there's the fixed baffle that will stay closest to the primary mirror. It got flat black spray-on paint on it. Under the baffle is the mirror box.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4157019 - 11/01/10 07:11 PM Attachment (40 downloads)

In this shot I put the bottom baffle more or less where it should be in the mirror box, and I placed the UTA on top of the baffle, in the mirror box.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4157059 - 11/01/10 07:32 PM

Beautiful work Olivier !
This is gonne be one of the most neat scopes I've seen in a while.


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Re: My very late 14 inch f/5 project... new [Re: neo]
      #4157076 - 11/01/10 07:39 PM

Thank you Alex

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4166435 - 11/05/10 09:08 PM

Nice

The collimation of the mirror cell is taking shape: it will be a push-pull sort of cell.

Tonight I drilled the holes for the push-pull and screwed the threaded inserts in place for the push bolts (metric M6 thread). I now need to get some standard hardware parts to complete the push-pull cell. Maybe I'll have to get some moderately strong compression springs as well. They should fit an M8 bolt. Either that or a stack of Belleville washers (if I can source them for an affordable price).

I also brought home the primary and secondary, since I will have to do some checks now, and I want to attach the secondary to the secondary holder as well.

Stay tuned


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4172295 - 11/08/10 05:27 PM

Apart from the Belleville washers and 2 tapped M5 holes for the cell I have now everything in place for the mirror cell.

Tonight I found the 8-32 screws in my letter box, hence I managed to install the spider in the UTA. Looks great now


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4191788 - 11/17/10 11:04 AM

Beautiful craftsmanship.

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Re: My very late 14 inch f/5 project... new [Re: Scanning4Comets]
      #4192388 - 11/17/10 03:11 PM

God bless you for having successful craftsmanship using a drill press such as that one you depict. I guess patience and care can go a long way to achieve the same results as a larger power tool yields.

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Re: My very late 14 inch f/5 project... new [Re: Hitech]
      #4193187 - 11/17/10 08:49 PM

Great work Oliver. And yes, it is amazing what can be done with a few tools - with the help of some Dremel magic!
Looking forward to what you do with the mirror cell!
Joe


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Re: My very late 14 inch f/5 project... new [Re: jpcannavo]
      #4198209 - 11/20/10 07:20 AM

Thank you all for your words of encouragement and compliments! If there weren't a dynamic and eager to share ATM community I'd never have been this far in my scope project.

I'll post some more pictures later, as some smaller things have been done now (including attaching the secondary mirror to its support).

Cheers!

Olivier


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4199015 - 11/20/10 04:14 PM

VERY NICE craftsmanship!

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Re: My very late 14 inch f/5 project... new [Re: mikeslater]
      #4199398 - 11/20/10 07:28 PM Attachment (34 downloads)

Thanks

Here are a couple photos to document my progress.

The UNC 8-32 bolts arrived a week ago, hence I was able to install the spider in the UTA cage:


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4199399 - 11/20/10 07:28 PM Attachment (34 downloads)

Time to attach the secondary mirror to its holder. I use a universal elastic mounting kit sold in Belgium under the brand TEC-7. In total 4 generous blobs have been applied, and matches serve as spacers.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4199401 - 11/20/10 07:29 PM Attachment (30 downloads)

The mirror cell now also features the 45 lateral mirror support. I used heavy duty L angle irons (3 mm thick) for the job. The irons were too long hence I had to trim off part with a metal hack saw. I measured the place of the lateral support by taking into account the thickness of the synthetic felt pads (not yet mounted). The lateral support points are implemented with nylon bolts, of which I sanded flat the head. The L irons were drilled and tapped with M5 threading. The L irons were placed at their correct locations by placing the primary on the mirror cell and carefully centering it. The 4 triangular cutouts served as precious guides in this exercise (I penciled the contour of the primary and the 45 orientation on the collimation board).

The 4 small rectangular metal tabs next to the 4 collimation bolt holes are stops for the push setscrews of the push-pull cell setup. One will not be used, but I leave the option to relocate one of the collimation point in the future.

I still need to trim the excess length of the nylon bolts. Missing in this picture are the mirror retaining clips (not yet built).

Edited by Olivier Biot (11/20/10 07:34 PM)


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4199413 - 11/20/10 07:35 PM Attachment (31 downloads)

The bottom of the primary cage has 2 cut-outs. Today I bought a sheet of 6mm birch plywood and had the "slanted" sides cut to size. The long sides must be milled at an angle: 30 at one side, 60 at the opposite side. To do so, I securely attached the angled Dremel Trio in my work mate. The angle of the Dremel Trio has been checked with the help of the triangular blocks cut off from the now slanted side panels of the primary cage. In this shot you can also see the straight edge clamped to the work mate. The slanted 6mm plywood sides will slide against this straight edge during routing (or milling).

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4199414 - 11/20/10 07:36 PM Attachment (27 downloads)

This is a close-up of the routing / milling of one of the 6mm slanted panels. This slanted edge will be in contact with the side of the mirror cell board. The other edge is still squared.

After this cut, the edge has been sanded clean.


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4199416 - 11/20/10 07:36 PM Attachment (29 downloads)

The second milling pass is a tougher edge to do since the router bit is further from normal than the previous cut. The principle is the same. To the far right you can see the hose of my vacuum cleaner. I clamped it to the work mate during the cut.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4199418 - 11/20/10 07:37 PM Attachment (26 downloads)

Each of the 4 triangles cut off the side panels of the primary cage serves as a guide for the collimation board, and will have the 6mm thick slanted panel attached to it. Here I am positioning the mirror cell board and the triangles with the help of some scrap wood having the same length as the inner section of the primary cage. I used the counterweights of my TAL mount to keep that board in place while measuring and placing the collimation board and the triangular guides.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4199419 - 11/20/10 07:38 PM Attachment (31 downloads)

The slanted 6mm thick boards are glued to the triangular guides with urethane glue. I had to remove the marine varnish from the side of the triangle in order to ensure a good glue bond. The glue needs 3 hours to cure. They still need to get marine varnish to the outside and flat black spray paint to the inside of the primary cage.

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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4199433 - 11/20/10 07:47 PM

Quote:

Time to attach the secondary mirror to its holder. I use a universal elastic mounting kit sold in Belgium under the brand TEC-7. In total 4 generous blobs have been applied, and matches serve as spacers.




Minor nit: never 4, always 3. That way, if the blobs pull at the mirror differently, there's no way it can be pulled out of the plane. Though I suppose the thickness will also avoid the issue, with 3 blobs you're sure.


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Re: My very late 14 inch f/5 project... new [Re: sixela]
      #4200150 - 11/21/10 07:06 AM

Quote:

Quote:

Time to attach the secondary mirror to its holder. I use a universal elastic mounting kit sold in Belgium under the brand TEC-7. In total 4 generous blobs have been applied, and matches serve as spacers.




Minor nit: never 4, always 3. That way, if the blobs pull at the mirror differently, there's no way it can be pulled out of the plane. Though I suppose the thickness will also avoid the issue, with 3 blobs you're sure.




You're right Alexis. Actually I don't know why I put 4 blobs. Anyway, the kit is elastic and has a thickness of 2mm. That, in combination with the 14mm thickness of the secondary mirror, should normally be no problem. If there is a problem, then I'll re-mount it with only 3 blobs.


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Re: My very late 14 inch f/5 project... new [Re: Olivier Biot]
      #4200172 - 11/21/10 07:35 AM Attachment (41 downloads)

The urethane glue cured well overnight. I trimmed and sanded the excess urethane glue. The slanted side panels are ready for coating. marine varnish to the outside, flat black spray paint to the inside.

My cell will be push-pull. The allowed travel for collimation will be kept minimal (a couple mm) thanks to the use of Belleville washers. They provide very compact and modular compression springs that can be stacked according to the desired level of stiffness and travel. I ordered 75 of them from the US as I can't source them here unless I run a business and have a VAT number (or unless I pay $4 for one washer)

As a consequence, the collimation "blocks" (stack of 2 plywood beams glued together and drilled for the push-pull setup) needed to be adjusted so they fit between the collimation guides (the vertical faces of the small wooden triangles against which th