Re: [ATM] Ready for polishing?

[Bill Marriott <bmarriott@pacbell.net>]

We rutinely have people polish with 9u finish, at the Chabot mirror 
workshop, as going finer, especially in an open room where everyone from 
80grit to polishing are located (yeah, not ideal) The risk of scratches 
is greatere than the gain in a finer abrasive.  If you can provide a 
very clean enviroment, and proceed carefully, you may be able to knock 
an hour or two off your polishing times, with a 6u finish. But, unless 
you grind and completely remove damage form 9u, you will still have pits 
from the 9u.  Lets see, subsurface damage is supposed to be twice micron 
size, so, 18-12=6u, so in theory if you grind off 6u of stock (.00025") 
you should be find.  That is not very much with pyprex.

BillMarriott

Rich Ball wrote:

> Mentors,
> 
> On my way to finishing the glass-on-glass part of mirror-making I ran out of
> 6 micron grit.  A friend gave me some 9 micron and 3 micron in its place.
> (8" f4.5 project, Pyrex blanks).
> 
> I have finished 8 wets of 12 micron and 8 wets of 9 micron and the finish
> looks marvelous, lustrous and smooth.    Can I go to pitch lap at this point
> or do I need one grade finer?  Tex says that powders as fine as 3 micron
> will not take out all the coarser pits and will leave pits that will take as
> long to polish out as if the 3 micron had not been employed.
> 
> What's the voice of experience?  If I need 6 micron I'll have to take the
> time to send away for it.
> 
> Rich Ball
> Oak Park
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> 

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