ATM Machine Grinding Advice Needed

[Alfredo Neves <arainho_cl@yahoo.com>]

Hi,

After completing my grinding machine, I started work
on an 8" mirror. Rough grinding to F2.8 took about 16
hours. I guess my main mistake was using too little
weight, initialy. After getting tired of so much slow
progress I switched to #60 grit with about 15kg
weigth. This speed up a bit and I was able to hog out
about 0.4mm per hour.

My questions are:

1. Should I use a coarser grit next time to hog out,
Or it is not worth the effort afterwards to get rid of
the huge pits?

2. When polishing I intent to do it, like my griding,
using the spinning method (fixed over arm, undersized
tool). I read that my pitch lap should not have off
center facets of the lap will not spin. Is this
correct?

3. Can I use the same symetrical lap afterwards for
figuring by stroking and not spinning? Or will that
cause zonening ?

P.S. Last night I had just finished #800 grit and then
I bumped the edge and got a 4mm chip off the edge. The
chip is really small and will be covered by the mirror
holding clips. But what a shame! It was becoming a
perfect mirror. I have to hold myself not to go back
to rought griding to get the chip out. I keep telling
myself that it is just my pride that wants to through
away all the invested hours because of such a small
blemish that will not affect the optical quality of
the optics.

Regards,

Alfredo






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