Re: [ATM] Reducing the outer zone in figuring

[Mike Lockwood <melockwo@uiuc.edu>]

Hi,

Arjan te Marvelde wrote:
> I've picked up the work on my 10", made a new lap and started off. There's a
> high outer 1" and a TDE now, and the similarity with this thread triggered
> this reply. I used to get good results with brute force TOT chordial strokes
> to quickly get the edeg down, but for some reason it doesnot appear to work
> now. I've been trying Mike Lockwoods' trailing edge pressure strokes, but no
> effect.

That "trailing edge pressure" stroke is meant to fix an oblate sphere 
(let's call that condition negative correction), and is not meant for 
use on a mirror that's elliptical or nearly parabolic (positive 
correction).

What is the figure of the mirror you're working on?

> Sooo, I'm a bit confused now, and looking for advice... The above stroke is
> MOT, right? I presume the work is done where the tool edge is.

To correct the outer zone in figuring (which I try to do first, rather 
than last) I use the portion of the parabolizing stroke that has long 
nearly COC strokes, MOT.  See my full-size lap figuring page, linked 
from my home page.

	Mike L.

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