Re: [ATM] polish time for 13 inch

[Kevin MIchael Zabbo <chaosopher23@yahoo.com>]

Polish time depends on the polishing lap and agent
used.  I use a soft-ish pitch and zirconium oxide and
get it done in about 12 hours total time.

Figuring is another story, time could vary between
done with polishing and years later, depending on luck
and skill.  Only pure luck can get that parabola the
first time with no further figuring.

Kevin of Central MS
Found that thar darkness (to use the local dialect)


--- Mike Lockwood <melockwo@uiuc.edu> wrote:

> Hi,
> 
> Mel Bartels wrote:
> > Try a one inch oversized lap and see if turned
> edge magically disappears.
> > From a symmetry view, the turned edge, if it's
> going to occur, is moved off
> > the edge of the physical mirror into a larger
> virtual edge, which doesn't
> > exist when the mirror is used to focus light.
> 
> As Mel mentioned the magic 6:5 ratio has been
> written about before, in 
> the ATM books, I believe.  I seem to recall it in a
> chapter about 
> Hindle machines, though I could be wrong about the
> location.
> 
> I would like to point out that many of us make
> mirrors with laps about 
> the same size as the mirror, and I personally don't
> get turned edges 
> if the pitch lap is in contact.  The laps I use run
> from 100% down to 
> ~25% of the mirror diameter, depending on the
> mirror.  For large 
> mirrors the oversize laps become more of a
> challenge.
> 
> For the softer pitch that I use, cold pressing is a
> necessity or else 
> bad contact leads to unpredicatable results.
> 
> The moral of the story is that there are many, many
> ways to make a mirror.
> 
> F/3 is challenging.  The tolerances for measurement
> are much more 
> demanding than with slower mirrors, so it is more
> difficult to 
> determine the true shape of the surface with methods
> like Foucault 
> testing after the error starts to approach
> ~1/4-1/8th wave.
> 
> 	Mike Lockwood
> 
> 
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
> 


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