[ATM] Re: ATM Digest, Vol 14, Issue 27

["Greg Jones" <gregj888@comcast.net>]

Mark,

Funny you should mention this.  I just poured (well heat lamped) a 6" lap
for the 4.25 tertiary for my Tri-scheifspiegler (6").  I have used a
oversized lap a few time but always on a machine.  I start with a hot lap
and no weight; move the mirror so the whole surface is pretty much to the
curve.

Once it's cooled (still warm) place on the machine with light weight and add
weight as the lap firms.  Don't stop the mirror for very long on the lap as
it will deform a portion of the lap.  No need to press once running, just
keep feeding polish.  The 4.25 is waiting to go on the test stand to check
for ROC.  Those I've done in the past have come out of polishing a pretty
good sphere.  Still need a standard lap to figure.

BTW, the last couple of laps I've made by pouring smashed but hard pitch
onto the mirror then putting the mirror under a heat lamp.  Seems to work to
8"...  4" took about 5 to 8 minutes.

Greg Jones
------------------------------

From: Mark Holm <>
 I have a
mirror pair for a 4.25" scheifspiegler sitting, that I started long ago
and never finished.  Getting those reliably to spheres, especially the
convex, would be a good thing.

Mark Holm
mdholm@telerama.com

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