Re: [ATM] Removing perforated center

["Scott Milligan" <starzkey@charter.net>]

Bill:

Although I don't have any magic to share with you re removal of plastered
cores, I do have a suggestion that might help you avoid such situations in
the future; wax the core to a backing plate (Universal Photonics "stacking"
wax or similar) , then attach this assembly by waxing around the core
perimeter and between the backing plate and rear surface of the optic.
After completing the surface, remove the core by applying heat (gentle oven
soak if glass has non-zero CTE, otherwise a torch works fine and is safe).
Any wax residues can subsequently be removed using acetone or similar
solvent.  

Also, for what it may be worth, I just recently finished a 16" parabola with
a 4" hole through the center without blocking a core of any kind; I was
pleasantly surprised to find that edge roll-off around the hole was minimal
in both magnitude and extent, provided I kept the lap diameter around 50% or
larger.  Using a large lap on a flat with a small hole, I would expect edge
"roll around the hole" (I could have had a career as a songwriter...) would
be virtually nil.


Scott Milligan, heretical advocate for a plasterless ATM experience...


 

-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf Of
Bill Marriott
Sent: Wednesday, June 14, 2006 3:29 PM
To: atm@atmlist.net
Subject: [ATM] Removing perforated center

Hello;

I just finished a 8" flat with a center hole, held in place with plaster of
paris.

Looking to release the core with out downgrading the glass, so re coring I
think is too risky, so;

Since I have a variety of chemicals here in the optical shop, any
suggestions as to what might attack the plaster, but not the Pyrex.

I have HCL, nitric acid, acetic acid, KOH, NH4OH, (the latter two would
probably etch the Pyrex), TSP,

For now, just going to toss it (haha) into a tank of water and let it sit
overnite, to see how far the water will soften the plaster.

Any suggestions are greatly appreciated

Bill Marriott
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