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Author Topic: CNC telescope mirror grinder.  (Read 13802 times)

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ynneb

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CNC telescope mirror grinder.
« on: December 06, 2006, 06:35:05 AM »
Recently I bought a new telescope for my son. It has a 12 inch diameter mirror.
While the telescope looks expensive because of its size (6 feet long), essentially its a tin can with a big mirror and a few lenses.
The most expensive part of the telescope is the mirror. It probably makes 80% of the cost.

I am told these mirrors so ground accurate that even cleaning the dust off then should be kept to a minimum so as to avoid damaging their tolerances.
I am also told that they must be ground by hand by counting and using a certain pattern.

I am wondering is they could be ground using CNC methods, and at the last stages be ground using the hand method.

Does any one know much about this process, or know of any good links ?
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Offline Graham Waterworth

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Re: CNC telescope mirror grinder.
« Reply #1 on: December 06, 2006, 08:35:18 AM »
I would stay away from the guys that made the Hubble one.  ;)

Graham.
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Offline fer_mayrl

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Re: CNC telescope mirror grinder.
« Reply #2 on: December 06, 2006, 12:22:24 PM »
Benny,
About 5 or 6 months ago, there was a discussion in one of the yahoo groups about a guy trying to do this. Cant remember if it was in the DIY-CNC, CAD_CAM_EDM_DRO, or the mach group. I think he was talking about bigger than 12 inches, and tolerances that scared me.
Regards
Fernando
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Offline chad

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Re: CNC telescope mirror grinder.
« Reply #3 on: December 06, 2006, 06:02:38 PM »
Hey just after a quick google search i found this site. Lots of info and she is in your neck of the woods.

I would have thought it to be impossable for the home brew guy but maybe not. 

In case you haven't found it yet here is the link.

http://www.turbofast.com.au/astrotel/index.html

some others


http://vegas.astronomynv.org/Tutorials/MirrorGrinding.htm

http://www.newportglass.com/

Looks like it could be fun. you will need art to write a "random function for you" and steppers might be a problem because of the indents in the stepper.

 :P
Chad

Found some more

http://www.stellafane.com/

http://home.thezone.net/~dbourgeo/feb/feb-2001-talk.html

Then all you would need is to get a nice ccd to mount to the end , then use mach for the dec and az and you could have a mach controlled self tracking telescope.

My big question is how you do the e beam vacuum deposition for the metalized layer and then the subsequent Ar coating at home.  (used to work with lasers and in a planetarium)


« Last Edit: December 06, 2006, 06:13:19 PM by chad »
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Offline Chaoticone

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Re: CNC telescope mirror grinder.
« Reply #4 on: December 06, 2006, 09:36:57 PM »
I think he will do that with that metalized thingamajigey, some saran wrap and a hoover. ;D
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Offline chad

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Re: CNC telescope mirror grinder.
« Reply #5 on: December 07, 2006, 03:29:07 AM »
LOL

chad
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Offline JDolecki

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Re: CNC telescope mirror grinder.
« Reply #6 on: December 11, 2006, 04:42:18 PM »
DUH. You would use a Langstrum 7 inch gangley wrench to apply the e-beam AR deposition coating.
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ynneb

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Re: CNC telescope mirror grinder.
« Reply #7 on: December 11, 2006, 05:51:11 PM »
I just realized I havnt responded. Thanks for the links guys. I thought I was a good Googler but you have returned better finds than I did.

The whole thing was a passing thought. I probably wont build a grinder. Still Its fun to think about for 24 hours :)
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Offline polaraligned

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Re: CNC telescope mirror grinder.
« Reply #8 on: December 12, 2006, 09:02:34 AM »
There are commercial grinding and polishing machines out there.
http://www.kennedy-optics.com/shop.html
Here is a picture of a couple of them.
The final "figuring" is what needs to be done by hand.
A professional can easily spend 200 hours or more
working on one of these large mirrors.  A large amateur mirror
is anywhere from 16" to about 32", though others may have
slightly different opinions.   A 32" will cost you from $13,000 on
up. 
And yes, they are ground to high tolerances....to the tune of
several millionths of an inch. 

Scott
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Offline Pete

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Re: CNC telescope mirror grinder.
« Reply #9 on: December 22, 2006, 07:02:38 PM »
I believe this was posted on the PM forum some months ago....

"Worlds Most Accurate Lathe", and yes, it is for optics. Accuracy down to one millionth of an inch!!!

http://www.llnl.gov/str/April01/Klingmann.html
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