Re: [ATM] figure stroke ten inch

[Tom Fredrickson <newsforfred@comcast.net>]

On Tue, 23 Oct 2007 12:45:22 -0500
Mike Lockwood <melockwo@uiuc.edu> wrote:

> Tom,
> 
> Tom Fredrickson wrote:
> > I have made a new lap with softer pitch and the figure is very good.
> > I now have a problem with surface roughness. Could this be caused by
> > the fresh lap? It is so bad that it distorts the lines when doing a
> > ronchi test. My plan is to mix up some fresh cerox and just spend
> > some time polishing. Should I use COC stroke work back toward a
> > sphere?
> 
> Usually softer pitch leads to less surface roughness, because the 
> pitch conforms more quickly to the aspheric mirror surface.  So, 
> something is not right.  Are you using lots of polishing force, or is 
> the lap not entirely in contact?  Does the lap/mirror slip and grab 
> during polishing, or is the drag consistent and smooth?
> 
> Yes, if you have made the mirror as rough as it sounds, you should 
> smooth it out a bit.
> 
> 	Mike Lockwood
> 
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> 

Mike,

I have changed my method. Now using long press to start with no heating
of the mirror or lap. Slower strokes with the least pressure possible.
fresh  crox that is diluted with more water. stop and press if contact
gets bad.

Before I did notice more slip and grab. I think major problem was
poor contact.

Tom

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