[ATM] The Ultrathin 15.5 Project

[vorblesnak@peak.org]

> I think that this will be interesting to follow.
> First scaring prophecies are already done. In my opinion
> you will end up with lot of experience and if reported properly
> extensively and accurately it will have value for ATM.

I hope it will be of some value.  I am very poor at documenting what I
have done.  I will have to improve on that.  If I can get it to mirror
quality my intent is to mount it in an extremely light weight tube.  I am
notorious for using pink rigid foam to make scope tubes.

> While sufficiently thick mirrors hold themselves to great extent,
> in your case this will be the main problem.

It is an odd feeling to feel the bumps of the tool though the glass.

> Perhaps you should grind and polish with minimum pressure that means very
> long time.

This is exactly the lesson I learned from the pie plates.  You must use
only the weight of the glass, or you must spead the weight uniformly over
the back of the mirror.

The mirror is always on top, always.  To put the mirror on the bottom
requires it to be perfectly supported, or astigmatism forms quickly.  With
a full size tool and the mirror on the top, the glass is fully supported
by the tool at all times.  Care must be taken, but astigmatism is less
likely.  The strokes are quite slow, more like polishing strokes, and very
gentle.

I have already begun to ponder the polishing cycle.  Some weight must be
applied for a proper polish, but that weight must be overall and
consistant.  Even the shaping of the lap will break new ground.  I may
resort to the techniques used by the metal mirror makers and make a
'buster'.  This is a tool with the exact shape of the mirror that can be
used for the heavy work of shaping the pitch etc.  Then press the mirror
and polish.  But this is all down the road a week or two.

> you will face the problem of the support of the mirror which has non-flat
> back and must be supported very well

I went down the mount and cell road with the 16 inch project a few months
ago.  That mirror is 5/16ths inches thick.  The mount was a very simple
disk with foam buttons at points determined by a PLOP 54 point design.

>
> You certainly have something to worry about but this is the essence of
> challenge.
>
> Regards
> Vladimir.
>


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