Re: [ATM] Tell me about scratches

["Rob&DonnaF" <TheFifareks@cox.net>]

Rich;
I used a similar type of tool for my 16 inch f4 plate glass mirror. I made a 
concrete full size tool by taking the mirror (after getting through with 25 
micron wao with a 1/2 diameter tool) and forming the concrete tool over an 
aluminum foil covered mirror. This gave me the curve to start polishing on. 
After curing, I use fiberglass cloth and polyurethane resin to seal the edge 
and back, but not the curve side. I overlapped the edge about two inches. 
Use a sander, outsidebecause of dust, and then redo the sealing one more 
time with resin only. I then poured the pitch directly on the curved 
concrete side. I also used two inch cellophane tape along the edge after 
finishing the pitch pour. this sealed the concrete tool very well, and was 
very durable. I cleaned this tool with water hundreds of time and because it 
was concrete, no water damage present. It was also nice to have the heavy 
tool when it came to polishing, aided in pressure required. Some of the 
pitch peeled off when it was tool cold to polish, and a small lip formed 
between the pitch and the glass. I found a small exposed spot of concrete 
after this, and sealed it by melting some pitch to cover it. Overall, it 
worked well, and would do the same for next mirror, although 16 inch seems 
to be limit on size due to the weight of the thing.
Rob F.
----- Original Message ----- 
From: "Rich Ball" <ShooterBall@hotmail.com>
To: "ATM List" <atm@atmlist.net>
Sent: Monday, November 22, 2004 10:20 AM
Subject: [ATM] Tell me about scratches


> Alas, now three hours into polishing my 8" f4.5 Pyrex mirror I find a 
> couple
> scratches.  One is not deep enough to feel with a fingernail.  One is. 
> It's
> about 1/4" long.
>
> It's all about pride I suppose. They won't damage the image.  But here's 
> the
> problem.  I'd go back to fine grinding and take them out.  I saved the 
> tool
> and made new concrete pitch-lap base.   But how do I protect against more
> scratches?  I have taken what I thought to be reasonable care.
>
> I'd like to hear from some glass pushers who manage to get through 
> polishing
> and figuring without these annoying and pride-damping intrusions.  What do
> you do to guard against them?  Is it possible to avoid them without access
> to an industrial clean room?
>
> Rich Ball
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> ATM mailing list http://www.atmlist.net/
> 


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