Re: ATM 8" refractor project

[Michael Lindner <mikell@optonline.net>]

On Friday 24 January 2003 12:37, David Margrave wrote:
> For the spherometer, there seems to be a lot of talk back and forth about
> what is suitable for a dial indicator/micrometer...

David,

Travers Tool (http://www.travers.com/) has micrometer heads that read down to 
0.0001" for $19. See parts 57-016-130 and 57-016-132. Having said that, you 
should decide what accuracy you need. Compute the spherometer reading you 
expect to measure from each surface, then take +/-0.0005" from that number 
and compute the resulting ROC. If that's within the tolerance of your design, 
you can get away with measuring to the nearest 0.001". If not, try again with 
+/-0.00005". In my case, I got away with a 0.001" dial indicator by making 
the spherometer large (7.5" base).

Not having access to a machine shop, I built my spherometer and wedge tester 
from square aluminum tubing, and used 1/4" stainless steel ball bearings 
attached to screw heads with JB Weld for the feet, and a dial indicator held 
in a hole by a set screw.

Caveat: this is MY first lens project, and it's not complete, so I can't swear 
that everything will work out fine if you follow these directions, but at 
least the micrometer heads are cheap ;^)

Clear skies.
-- 
Michael Lindner
ATM Site http://www.atmsite.org        TM Web Ring 
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