From: "James Lerch" 
To: "ATM List" 
Reply-To: "James Lerch" 


----- Original Message -----
From: "Jerry" 

>#1) Already Spherical
>
>I have had the same experience with all of my mirrors being quite
>spherical during polishing. But it does not last until completion of polish.

I can only comment on my observations on the students in our Mirror Making
class.  Over the last 2 years or so, and rapidly approaching 50+ mirrors,
I've noticed most of the students come out of polishing with an Oblate
surface (IE center of mirror focuses longer than Edge of mirror)   Most
usually have a
pretty smooth surface and a decent edge.

The biggest problem we run into is getting the students to Rotate and
Sidestep in appropriate amounts while grinding / polsihing / figuring. 
What usually happens is they rotate mirror 1/8 Counter clockwise, and
side-step 1/8 Clockwise
(or vice versa), and what happens is they end up working just two diameters
of the mirror (from both sides) as the total motion was 1/8 + 1/8 = 1/4. 
Debate rages on as what the "best" method of rotating and
side-stepping is.  I just find its interesting that human nature tends to
be rather repetitive (even thought its sub-conscious), while all the time
we try and be random ;)


> #2) How to Parabolize

Won't touch the strokes to use, other than to say what ever appears to be moving
all the zones by appropriate amounts, all the time keeping the edge in
shape. How do you know if its working?  Lots of pressing, short figuring
spells, and LOTS of testing (In a 4Hr class, we'll usually test 2 or 3
student mirrors 3 or 4 times each while they are figuring!)

> #4) When to Stop Polishing

After seeing Carl Zambuto's "Oh My, How'd he do that?" level of
polish, I currently have the belief that whatever amount of time it took to
get you to the
point where you "think" its polished out, Double that amount. 
Even then, I'm not certain you can get to the Zambuto level of polish (at
least by hand, machines maybe), Carl's method is pretty amazing thing to
see!

Take Care,
James Lerch

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