rboe
Numbfinger
Reged: 03/16/02
Posts: 39501
Loc: Phx, AZ
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Gene; you may not be able to answer this until you have used it but it appears to me that the CF panel is a bit thin to dampen vibrations and perhaps a foam core to make it much thicker would kill them off straight away.
I have no experience with CF so I have no real world experience to base that opinion on.  I am very keen on seeing how that works in the real world (where theory, at times, comes up short).
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Ron
NS11GPS
Pronto
16" dob
15X70 Obies
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Scott Watson
super member
Reged: 05/26/06
Posts: 170
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Quote:
As I have said before I dont think this mirror cell is original, it,s too simple and someone must have thought of it already. I have not seen one like it before though.
The main advantage is that the cell allows you to collimate the mirror or if you want you can move the mirror forward or backward an inch and a half. The design is simple , something that anyone could make.
the drawback to the design though is that the brackets have to be precise or the mirror cell will have tension on it, and also it has to be custom made for a paticular diameter tube.
The T-nuts are glued in the cell with silicone caulk. The reason is that when you move the cell forward there needs to be a slight ability to flex as you are moving the cell out of alignment with the bolts. So the holes for the t-nut are slightly over drilled and silicone in place to allow flex if needed. I think I will find another way to just use rubber washers here and somehow lock the t-nut in place. But this is just a prototype to see how it works.
Sometimes you dont see the flaws in a paticular design till it's made. I still need to test it under regular conditions and see how well it works moving the mirror forward and back.
This design could be modified to work with a regular mirror also.
I would be interested to hear your thoughts on this paticular design and any flaws you think it may have other than what I mentioned.
Another way to solve your problem of an overconstrained system is to use ball joints/inserts. Effectively it does what your silicon glue does, but with much much higher strength. They cost more too.
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Gene Hunter
super member
Reged: 12/29/07
Posts: 194
Loc: SC
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yeah I think the ball joints would make it more expensive. the whole idea is sorta to keep it simple, functional and yet have the ability to move.
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Clear Skies
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jpcannavo
sage
Reged: 02/21/05
Posts: 309
Loc: Long Island New York
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Gene
I think the issue of over-constraint may be a bit overstated here. If the optical tube is precisely planned, executed and set up, the actual amount of movement/displacement involved in collimation should be minimal, and will likely be accommodated by such things as flexure and play in your threaded components. In fact, sometimes this works in your favor by taking up such play/flexure and keeping things tight. (I actually took this concept to the extreme, in the cell for my old Royce 16, where various aspects of design were consciously over-constrained. This included a collimation mechanism operating at four corners of a rectangle cell, allowing a slightly ill-defined plane, so as to take up any residual play in the ball bearings I used!)
I love the one plate/no springs aspects of your design. I also think you achieve more lateral stability – for a given range of “travel” – than in the traditional two plate w/springs design.
I would stay with the simplicity and go ahead and test a prototype. And then, only complexify as dictated by necessity, since complexity itself often leads to other complications.
Joe
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Joseph Cannavo
16" F5 Zambuto, front collimating, scope nearly complete - WSP here we come!
16" F5 Royce, conical blank, front collimating (Mirror Sold)
10" F5 Dob
Mid 70's RV-6
4" Orion 100mm ED
Mr Keeyoots (My Cat)
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Gene Hunter
super member
Reged: 12/29/07
Posts: 194
Loc: SC
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Thank you Joseph, I appreciate the candid comments. I tend to agree with you that possibly the t-nuts should be premenantly glued in to the cell. In my bench testing anyway it seems that accounting for the flex may not be neccissary,
It would be up to the user to keep the plate square though, In my wildest dreams I can imagine someone trying to move the mirror an inch forward using one collimation knob at a time, this would be extreme and honestly would probably cause it to seize up as the threads would become stuck.
Its entirely possible though that an average user would never see this issue.
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Clear Skies
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NeoDinian
Experienced Postmaster
Reged: 10/05/05
Posts: 11997
Loc: Rockford Illinois
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Bringing up this thread again, as I'm seriously considering something like this design for my cell...
One thought though... Do you think that putting a spring on either side of the plate would help in stability and holding collimation?
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Neo... (Jeff)
-=-=-=-=-=-=-
10" LX200-GPS/SMT UHTC "Draco"
 Rockford, Il.
NeoDinian's Eye on the Sky!
Coming soon:
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Gene Hunter
super member
Reged: 12/29/07
Posts: 194
Loc: SC
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springs would limit the travel. I have done some testing and I dont think there is any backlash at that distance from the center of the cell. the backlash in the t-nut diminishes as the distance from the center of the cell increases. At the distance of 6 inches, i do think its minimal at most.
Also you could place nuts on one or both sides to lock down and tighten once you have the cell in the proper location. not that I think its needed.
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Clear Skies
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NeoDinian
Experienced Postmaster
Reged: 10/05/05
Posts: 11997
Loc: Rockford Illinois
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I understand that the limit of travel would be decreased, but we're still dealing with a lot of travel (At least more-so than a standard design). Using springs would be an easy means of giving some "Feedback" to the collimation process, and still leave plenty of travel. If more travel is required, the brackets can be made longer as well.
Yes, lock nuts of sorts would do well also, but adds another step to collimation.
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Neo... (Jeff)
-=-=-=-=-=-=-
10" LX200-GPS/SMT UHTC "Draco"
Rockford, Il.
NeoDinian's Eye on the Sky!
Coming soon:
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Spoonsize
Vendor/Clothing
Reged: 08/27/04
Posts: 2150
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I've got my cell assembled. I'm waiting for the arrival of the fiberglass extensions to continue. In the meantime, now that it is assembled, I see no way to add lock nuts and be able to reach them inside the tube. I'd already decided on some compression springs that will be about 2 inches long, unloaded and go on the focuser side of my mirror plate. This, after trying to figure a way to hold the plate firm, if you get my drift.
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Steve Durham
www.margesmonograms.com
(Marge made me do it)
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NeoDinian
Experienced Postmaster
Reged: 10/05/05
Posts: 11997
Loc: Rockford Illinois
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Pics?
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Neo... (Jeff)
-=-=-=-=-=-=-
10" LX200-GPS/SMT UHTC "Draco"
Rockford, Il.
NeoDinian's Eye on the Sky!
Coming soon:
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reodds
member
Reged: 05/04/06
Posts: 74
Loc: Merrick, New York
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Gene,
Your mirror cell is great, and I plan to use it on my 10" with a Royce conical mirror.
What (if anything) are you planning to do about mirror cooling? With a CF cell, there is obviously no thermal assist as in an aluminum cell.
Roger
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Roger
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Gene Hunter
super member
Reged: 12/29/07
Posts: 194
Loc: SC
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There is certainly nothing wrong with using aluminum. since its only one plate as opposed to two it will still be light weight. Also using aluminum you could tap the threads in the metal directly.
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Clear Skies
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reodds
member
Reged: 05/04/06
Posts: 74
Loc: Merrick, New York
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O.K. I understand aluminum is a good substitute, but I really do want to use CF. As a matter of fact, I am going to make an all CF scope. This might be an issue for a different thread, but are you planning to cool the mirror in your setup, and if so, how? You can PM me if you feel it necessary. Thanks
Roger
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Roger
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Gene Hunter
super member
Reged: 12/29/07
Posts: 194
Loc: SC
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Well with a royce mirror you really should have a cooling fan on the sides. I am guessing three smaller ones as opposed to one large one. trying to put a fan in the middle would be difficult. so just leave a cutout on the sides for a fan in three places.
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Clear Skies
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reodds
member
Reged: 05/04/06
Posts: 74
Loc: Merrick, New York
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Do you have a pic of your latest scope - the one you are using the cf cell?
Roger
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Roger
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reodds
member
Reged: 05/04/06
Posts: 74
Loc: Merrick, New York
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One more thing... If I decide on the aluminum varient instead of cf, what thickness do you think would be adequate for the 10" mirror?
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Roger
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Gene Hunter
super member
Reged: 12/29/07
Posts: 194
Loc: SC
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I am not sure on the aluminum thickness. perhaps someone with more experience with aluminum can answer that. I have seen people use 1/4 inch but I personally would use thicker. I always overbuild things myself.
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Clear Skies
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reodds
member
Reged: 05/04/06
Posts: 74
Loc: Merrick, New York
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Back to the CF idea again... Because of the inherent "sloppiness" of the t-nut, do you think enough movement for collimation could be achieved by gluing the t-nut into the CF with epoxy? This would make a more permanent fixture, and avoid possilbe silocon rubber degradation over time.
On another note, making for EP accessible collomation is porbably the best way to go. Does anyone have a good way of attaching fiberglass poles to the 1/4-20 nut on the plate?
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Roger
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Gene Hunter
super member
Reged: 12/29/07
Posts: 194
Loc: SC
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I think epoxy would work fine. Also a spring also would help to keep things tight.
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Clear Skies
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