Re: [ATM] Making the pitch tool

["John Stephen" <atmlist.net@johnstephen.org>]

Hooray, I made my pitch tool!  I didn't end up using the camp stove after 
all because it was quite windy out today and I was concerned about it 
blowing over (mine is one of those single-burner stoves that sits on top of 
a fat little propane bottle).  However, Richard Schwartz suggested using an 
oven at low temperature and that worked very well.  I was easily able to 
melt the pitch thoroughly in a "family size" soup can just until it was all 
melted, no fear of overheating it at all.  It did take a while to melt 
completely, probably half an hour or so.

I made one polishing pass on the mirror and stuck it on my focault tester 
only to find that the focal length is about two inches too short, making it 
approx. F3.75.  That wouldn't be a big deal except that I'm replacing an 
existing mirror (F4) and need to match it better than that.  In hindsight, I 
should have used the spherometer to measure the original mirror as a sanity 
check, but I foolishly assumed that the place I bought the spherometer from 
had verified its operation.  Stupid stupid stupid.

Now I've got to go back to rough grinding so thank jebus that I didn't 
re-use my tile tool as a pitch tool.

Thanks everyone for all the great tips on handling pitch.

- John


----- Original Message ----- 
From: "John Stephen" <atmlist.net@johnstephen.org>
To: "ATM List" <atm@atmlist.net>
Sent: Friday, October 15, 2004 1:11 PM
Subject: [ATM] Making the pitch tool


When making a pitch tool, how thick should I make the cerium oxide solution 
that I use to prevent the mirror from sticking to the pitch?  The solution 
for polishing calls for 1 tablespoon of oxide in 8 oz. of water, but photos 
of a pitch tool being made on the Stellafane site show a solution which 
appears to be much thicker than that.

Thanks,
- John
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