ATM Aluminum Mirror Project

[Jack Schmidling <arf@mc.net>]

Finally got the aluminum mirror to the polishing stage thanks to the
grooved tool.  Grinding at all stages proceeded normally with none of
the sticking in the later stages that brought the previous attempt to
a halt.

I tried (after a fashion) Val's paper lap but got nowhere with it.  The
upper surface just shreded up like wet paper and didn't work at all.  I 
did not glue  it down as recommended because there seemed to be enough 
adhesion to the aluminum tool without.  The glue just might hold it all 
together so it may not have been a valid test.  As I already had a pitch 
lap ready to use, I didn't bother going any further with the paper.

The pitch lap performed normally this time and there was no difference
between the feel with the aluminum mirror and pyrex this time either.
First time, it stuck to the lap to the extent that the only way I could
polish was by leaving the nylon subfaceting net in place.

Unfortunately, polishing is not going very well and after about an hour
or so, I just have a dull grayish surface.  It does not look like it will
ever be a silver like surface and I think what is happening is that the
micropits are filling up with the mud or the mixture is creating some 
unshiny alloy or chemical reaction.

Within minutes of beginning a polishing wet, the polish turns gray and
I have to keep flushing the lap with fresh polish.  It must be removing
aluminum at a prodigeous rate and oxidizing in the water and creating
a hopeless mess.

Examination of the surface at high magnification shows lots of pits
of every possible size.  I suspect it is the nature of cast aluminum
and not related to fine grinding as I over did this just to make sure.

Anyway, I will continue but have lowered my expecations substantially.

js
 

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