Re: [ATM] Pitch Substitute for very fast mirrors

[Mike Lockwood <melockwo@uiuc.edu>]

Hi,

Kevin MIchael Zabbo wrote:
> Pitch does have a lot of useful characteristics that I won't get
> into here, but it has a flaw that I need to point out. Fast and
> large mirrors, say 13" f/3, have a deviation from sphere that can
> be measured on a decent micrometer, which is far too big a gap for
> pitch to conform.  The pitch, even if soft, takes a long time to
> flow.

What size pitch lap are you using?

It is difficult to do anything faster than F/4 with a full-size lap. 
You can get the correction started, but that's about it.

I used pitch (on subdiameter laps) that wasn't even super soft (just
kind of soft) on a 20" F/3.3 and I had no problems at all.  Pitch has 
been used down to F/2 and below with appropriate techniques.

I also agree that a good amount of pressure, slow strokes, and soft 
pitch produce nice, smooth surfaces.

	Mike Lockwood

_______________________________________________
ATM mailing list http://www.atmlist.net/