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Equipment Discussions >> ATM, Optics and DIY Forum

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Olivier Biot
Amused
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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
Amused
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Reged: 04/25/05

Loc: 51°N (Belgium)
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
Amused
*****

Reged: 04/25/05

Loc: 51°N (Belgium)
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
Amused
*****

Reged: 04/25/05

Loc: 51°N (Belgium)
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
Amused
*****

Reged: 04/25/05

Loc: 51°N (Belgium)
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
Amused
*****

Reged: 04/25/05

Loc: 51°N (Belgium)
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
Amused
*****

Reged: 04/25/05

Loc: 51°N (Belgium)
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
member


Reged: 04/07/09

Loc: Gloucester, UK
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
Amused
*****

Reged: 04/25/05

Loc: 51°N (Belgium)
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
professor emeritus


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
Post Laureate
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Reged: 04/01/08

Loc: Lovettsville, VA
Re: My very late 14 inch f/5 project... [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
Metal Whisperer
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Reged: 11/07/04

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

Construction looks great Oliver!

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rboeAdministrator

*****

Reged: 03/16/02

Loc: Phx, AZ
Re: My very late 14 inch f/5 project... [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
Amused
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Reged: 04/25/05

Loc: 51°N (Belgium)
Re: My very late 14 inch f/5 project... [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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Reged: 03/16/02

Loc: Phx, AZ
Re: My very late 14 inch f/5 project... [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
super member
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Reged: 03/04/05

Re: My very late 14 inch f/5 project... [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
professor emeritus


Reged: 11/24/07

Re: My very late 14 inch f/5 project... [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
Amused
*****

Reged: 04/25/05

Loc: 51°N (Belgium)
Re: My very late 14 inch f/5 project... [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
Amused
*****

Reged: 04/25/05

Loc: 51°N (Belgium)
Re: My very late 14 inch f/5 project... [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
Amused
*****

Reged: 04/25/05

Loc: 51°N (Belgium)
Re: My very late 14 inch f/5 project... [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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