Re: [ATM] Mirror clips

[Jason Hissong <jhissong@gmail.com>]

Hi Mike,

Well, I started figuring, but I am having trouble keeping things secure 
on my turntable when I am at a large overhang, so I got some zones 
starting to happen.  The surface is getting a little rough from things 
not being very secure.  However, after the first session of figuring the 
slight oblate sphere became more spherical.. i.e., the center finally 
started to deepen so that it was meeting up with the raised zone.  It is 
neat to actually see things change like they are.  I think I solved my 
turntable problem... however, there is still a turn down edge that I may 
work on.  Going back to some polishing strokes to resolved that.. I 
could also just mask it as my mirror is really an 8.125" mirror and it 
looks like just the outer 1/8 is turned down?

http://www.undermidnight.com/images/atm/sphere_3.jpg
http://www.undermidnight.com/images/atm/sphere_3_oroc.jpg

As far as the mirror clips go... thanks for the tips (that goes for 
everyone!! chuckle)  I will try to keep the material coming... lol

I was going to use felt or cork for the surface that would touch the 
mirror, but I like your idea Mike.

As an aside, I want to thank folks like you, Bob, etc. who have provided 
some great material on the web for beginners like me.  I have your 
typical telescope making books.. but Mike, your explanation on figuring 
made the light to go on and I think I have a very good idea on how the 
various strokes work.  I will probably stick to Ronchi diagrams as it 
seems to be easier for me.. I am having a hard time with the couder mask 
interpreting when I have a particular zone nulled.  It seems that 
matching ronchi pattens are only slightly more subjective than a 
foucault test (at least for me) and easier .  The matching ronchi 
diagrams for my mirror are exact (in terms of a spherical surface).  The 
amount of lines and everything look like the diagrams except for the 
turned edge.

Also, I got my 13 year old brother interested... he is now working on a 
6" mirror.  So we are building scopes together.

Thanks again guys.. I will post my progress..

Jason Hissong



Mike Lockwood wrote:

> Jason,
>
> How is the figuring going?
>
>  
>
> I swear - only serious answers here....
>
> I try not to have ANY metal touching my optics.
>
> I like to use small pieces of non-brittle plastic for the clips, and I 
>  angle the underside so that they have the same angle as the bevel of 
> the mirror.  Therefore, they only contact the mirror on the bevel, not 
> on the optical surface, and I don't get marks on the coating from the 
> mirror rattling against the clips.  I extend the clips 1/16-1/8" over 
> the optical surface, and secure with a bolt/screw.
>
> The overall shape of the clip ends up like:
>
>  ---------------
> |              |
> |             /
> |            /
> |           /
>  -----------
>
> The best type of plastic for this is a type that is slightly soft, but 
> is still hard enough to drill and tap.  It is not brittle type that 
> will crack under pressure.  I got some white plastic at a plastic 
> supply place that is a little softer than PVC.  Might be Nylon. Teflon 
> would probably work, too.  Typical clip dimensions are 1/2" wide by 1" 
> long by 1/2" tall, again with only a little extending over the 
> mirror.  The plastic can be cut with a hacksaw or fine-toothed hand 
> saw.  A sharp knife cleans up the corners/surfaces.
>
> For you, an 8" mirror is light and the structural requirements for the 
> clips will be minimal.
>
> By the way, typically all the support points in my cells are small 
> teflon pads.  That is only one way to do it, but it works for me.
>
>     Mike Lockwood
>
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
>
>  
>

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