Re: [ATM] Help me get back to sphere

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

The hyperbola land is something that we all get into now and then.  I spent
this morning watching a guy taking down the hyperbola on a mirror -
difference between center and edge was about .4" with a TDE on top of that
for another .5" or so.  He's using the short half stroke and a hard lap.  He
got there because he decided to figure a mirror with the machine he has and
left it running for more than a few seconds - figuring happens quite fast
when the difference between center and edge is on the order of 0.05"!  Just
a few strokes of careful directions and so forth are needed.
At the present (1 hour of polishing and inspection) he is down to about 1/2
of the hyperbola with a large flat ring and the center hole and TDE left to
go.
Another guy is taking care of his problem hyperbola with a subdiameter tool
and attacking the high zone expressly.  He is getting all kinds of minor
zonal differences (the Foucault test looks like a bunch of rings on the
mirror) but those will go away with a quick pass with the full lap after
he's got the high spots down to about the right level.
Remember that the basic idea of figuring is that you rub hard on the high
spots and that brings them down into compliance with what should be.
Bob May
http://nav.to/bobmay
bobmay@nethere.com
NEW! http://bobmay.astronomy.net


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