Re: [ATM] stroke length

[Mike Lockwood <melockwo@uiuc.edu>]

Hi,

Frans Franssen wrote:
> In parabolizing a mirror with long W strokes MOT, starting from a
> sphere, is there a formula that determines how far the center of the
> mirror should stay away from the edge of the pitch lap, assuming a full
> diameter lap is used. I cannot find this information for my 10" F 5.2
> mirror. Thanks for your replies.

To start with, I'd recommend about keeping the center between 1" and
2" from the edge of the lap.  I'd favor about 1" from the edge when 
you're polishing center-over-center (at the end of the strokes), and 
2" from the edge when you're at one side of the stroke.  This will 
help to start correcting the edge, and hopefully avoid digging a hole 
in the center.

You need to work for a while (5-10 minutes) and then test and see how 
it's going and adjust your technique.

> Jonathan Bishop wrote:
> I've always been surprised how people can parabolize with a full
> sized lap. Never had much luck with that. I
> seem to be able to get within 1 wave or so but then have a hard time
> controlling more precisely the results.

These are both related.  Many others ask similar questions on the 
list, as this is how first mirrors are usually made - full-size tool, 
mirror-on-top W-stroke.

I will start writing up a web page tonight about parabolizing with a
full-sized tool, and post it on my site in a couple of days.
Hopefully that will answer a lot of questions for beginning mirror
makers and save some list traffic.

	Mike Lockwood



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