Re: [ATM] Tool surface medium

["Bob May" <rmay@nethere.com>]

Lockups generally occur because the two surfaces are not to the
same curvbe.  As a result, the space between builds up a vacuum
as the hole in the mirror travels from the edge to the center.
This holds down the glass more and more as the vvacuum builds,
eventually getting to the point hwere it locks up as the force to
move the glass is too high for you to move it.  The correct
solution is to work the middle high areas by doing short strokes
so that the two surfaces get back into shape relative to each
other.  Generally I've noted whenever this happens is that there
is also astigmatism that goes along with this as certain
orientations of the glass and tool don't want to lockup.  When
this haappens, it is easier as you jut keep the glass slowly
rotating and that will work its way out gradually.  You do need
to take care that the two don't lockup tho as well as that you
just don't go shifting the easy direction around as you go.
Short strokes again are what is necessary.
Remember that as long as you are doing long stokes, you are doing
strokes that will parabolize or worse in the polishing/figuring
stage.  You want to make the mirror and tool spherrical so you
need to use shorter strokes to maintain that shape!
Please note that when I say short strokes, I also mean not as
much side to side on the W part of the stroking.
Bob May

rmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net


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