Re: ATM Machine Grinding Advice Needed

[Anthony Stillman <atmer@flash.net>]

Alfredo,

>From the top...


>...grinding machine...8" mirror...F2.8 took about 16 hours.

That's about 18 cubic inches of glass in 16 hours.

Since you made your own grinding machine, if you plan on doing a lot of
glass, you might want to make a generator.  Generating glass is much faster
and is saves on grit.


>...switched to #60 grit
>...use a coarser grit next...?

It's not just the pits.  It's the sub-surface damage.  That is, it's not
what you can see, it's what you can't see.  It's imperative that these
sub-surface fractures are removed.  I know of only two ways to be sure that
they are.  Time spent grinding at finer grits and acid etch.  After I've
worked at 60, and that's been rare, I have done a couple of hours at 80 and
then double time at 120.  Was that too much?  I don't know.  I do know it
was enough.  As for an acid etch, I've never even considered using HF as an
ATM.  I think those who have used it, as amateur's or otherwise, are nuts.


>...my pitch lap should not have off
>center facets of the lap will not spin. Is this
>correct?

Free spinning laps will do what ever they want.  Sometimes the behavior
appears to be chaotic, but mostly it's just random.  Off centering the
channels/facits is a good idea so as not to produce ring zones.  Whether or
not this happens depends on the stroke.

As for motor-machines versus man-machines.  I've seen the same behavior and
results with both, i.e., good and bad.  It takes less time for an operator
to screw up with a motor-machine.  Curiously, both often make the same
sound when they do screw up.


>...a 4mm chip off the edge...will be covered by...clips.

I refer to these as alignment fidutials.  They are a necessary part of
determining the orination of any stig that may be persent. ;)


Anthony