Re: ATM How do I make a pitch lap

["Mel Bartels" <mbartels@efn.org>]

When channeling a pitch lap, ridges are formed on each side of the 
channel.  Pressing the mirror causes pitch squares that have small 
depressions in their centers to form.  These centers are higher than 
the bottom of the channel, so after a little polishing, these dimpled 
centers go away.

A picture of a 30" pitch lap of mine is at
http://zebu.uoregon.edu/~mbartels/scopes/pitch.jpg 

The lap is after some polishing, the center dimples have gone away,
and the channels are starting to close. Because of the convexity of
the curve, the soaped aluminum channeling tool is rocked from side
to side, resulting in less than straight lines.   Some channels are
opened by slight scraping with an X-Acto knife.  As you can see, the
pitch lap does not have to look perfect in order to work well.  It
is hard to get very large pitch laps to look perfect and have good
contact over all 30" of an f/4 curve! 
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With Regards, Mel Bartels, programmer/analyst, amateur astronomer
mailto: mbartels@efn.org   homepage: http://www.efn.org/~mbartels

How To Computerize a Dob: http://zebu.uoregon.edu/~mbartels/altaz/altaz.html
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