From: Michael Lindner 
To: David Margrave , atm{at}shore.net
Reply-To: Michael Lindner 


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
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