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Equipment Discussions >> ATM, Optics and DIY Forum

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Benach
Pooh-Bah


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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Reged: 03/16/02

Loc: Phx, AZ
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
Amused
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Reged: 04/25/05

Loc: 51°N (Belgium)
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
Amused
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Reged: 04/25/05

Loc: 51°N (Belgium)
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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Reged: 04/25/05

Loc: 51°N (Belgium)
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
Amused
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Reged: 04/25/05

Loc: 51°N (Belgium)
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
Pooh-Bah


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
Amused
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Reged: 04/25/05

Loc: 51°N (Belgium)
Re: My very late 14 inch f/5 project... new [Re: Benach]
      #3979333 - 08/12/10 05:38 PM Attachment (64 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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Reged: 04/25/05

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


Reged: 01/24/08

Re: My very late 14 inch f/5 project... [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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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: 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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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: Olivier Biot]
      #3981285 - 08/13/10 04:48 PM Attachment (51 downloads)

Here's a front view:

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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: Olivier Biot]
      #3983815 - 08/15/10 05:38 AM Attachment (41 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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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: 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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Benach
Pooh-Bah


Reged: 01/24/08

Re: My very late 14 inch f/5 project... [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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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: 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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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: Benach]
      #3983870 - 08/15/10 06:52 AM Attachment (43 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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Benach
Pooh-Bah


Reged: 01/24/08

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