[ATM] Figuring with sub diameter lap

[rozer at pacbell.net (Richard Ozer)]

I'm working on a 14" mirror with a subdiameter lap.  I would highly
recommend making a full sized lap.  However, if you want to give it a try
with the sub-diameter, then work with a W stroke.  Center over center with a
subdiameter tool will add correction, a W stroke that concentrates more on
the edge than on the center will tend to flatten it out.

If you have a ronchi grating, you'll find it quicker to use than a knife
edge for monitoring your progress.

RO

----- Original Message ----- 
From: "Jonathan Bishop" <jonathan_bishop@sbcglobal.net>
To: <atm@atmlist.net>
Sent: Monday, March 08, 2004 5:14 PM
Subject: [ATM] Figuring with sub diameter lap


> Hi,
>
> I am currently figuring an 8" F5 mirror using my old
> 4.25" lab left over from when I polished my first
> mirror. The defect I am working on is a sever
> overcorrection, so I am attempting to reduce the 70%
> zone.
>
> So far it is going well, which is encouraging. I am
> wondering whether many others use a sub diameter lap
> to figure with. It seems reasonable as you can easily
> direct you polishing to the zone you need to work on.
>
> Jon Bishop
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