Re: [ATM] Open Question Concerning Pitch Laps

[Jarvis Krumbein <jkoptic@juno.com>]

Bryan, I'll leave the pressing and surface questions about the lap to the
others as all the comments and questions so far are the same that I would
give.  As to the decentering of the facets, the reason is quite simple. 
If you center the facets (or channels) you do run the risk of wierd
zones.  This is due to symmetry of the facets (or channels).  Decentering
the facets helps to insure the surface is worked evenly and is not
affected by having the facets (or channels) always working on the same
parts of the surface.  This is the same reason that you vary the rate
that you walk around the barrel, rotate the mirror (or tool) and vary the
stroke slightly while you work.  In other words, random is good and
avoids problems.  Great regularity and consistancy is bad and leads to
zones.  As to the last, your hole (if it's a hole and not a hill) is not
a zone problem.  Zones usually appear as rather sharply defined
discontinuities.  An example would arise from a centered facet lap worked
very regularly which might produce zones that look like rings regularly
spaced.

Jarvis Krumbein


On Mon, 28 Feb 2005 20:38:53 -0500 Bryan Stiles <bryan.stiles@gmail.com>
writes:

> 
>  Another thing I had a question about. I've read everywhere to
> decenter the center facet of the lap and I've tried to do this with
> the two laps I've made. My understanding is that failure to do this
> will cause "zoning" of the mirror. My question is, what exactly is
> zoning? Could this be a contributer to the central hole in my 
> mirror
> since my lap was getting close to violating this cardinal rule?
> 
> I'm embarrassed to ask such simple questions but I just don't know?
> 
> 
> Thanks Again, Bryan
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