Re: [ATM] Open Question Concerning Pitch Laps

[Michael Lindner <mikell@optonline.net>]

On Tue March 1 2005 9:25 pm, Mark Holm wrote:
> If you want to go the mesh pressing route, many people use onion bag...

Sorry if I'm repeating a few things here - I've been away from this discussion 
for a few days.

I use fiberglass window screen for microfacetting laps. Here's what I do. 
First off, if the channels are closing up, or any pitch is hanging out where 
it will go over the mirror's bevel during pressing, trim it. Next, I take the 
lap, and under cool running water scrub the surface fairly aggressively with 
a clean brass brush until it is uniformly dark and scratchy. Set the mirror 
face up, place a section of screen on top (larger than the mirror) and 
liberally wet with cerox solution. Go back to the lap, and gradually warm the 
water up until it is as hot as your hands can stand it. You can soak the lap 
in this temperature water for a minute or two, or just hold it under the 
running water. Place the lap face down and add weights - lots of weight (I 
use about 40 pounds on an 8" lap). In just a few minutes I have a beautiful 
microfacets all over the lap. If I don't, I press longer. I remove the 
weights, lap, and the screen and replace the lap and weights without the 
screen. Press for about a slightly shorter amount of time.

A well pressed lap should have excellent contact. You should be able to move 
the lap in any direction in any orientation, and feel smooth even friction, 
without any grabbing or slipping. With a well pressed lap, and the right 
stroke length and offsets (you can measure with a ruler where the ends of the 
stroke should be and mark it on the work surface, so when you are taking a 
stroke you will stop at the right place), I find the figuring process goes 
according to "theory". Without either a well pressed lap, or with the wrong 
stroke, my results were very inconsistent.

Hoe this helps - clear skies!
-- 
Michael Lindner
http://www.starastronomy.org *** http://home.att.net/~mikel
http://www.atmsite.org *** http://www.atmlist.net
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