Re: [ATM] Richard's blanks...

[Dominic-Luc Webb <dlwebb@canit.se>]

Slumped blanks I have gotten had pits, and even a little lopsidedness,
but nothing I was alarmed about. I have so far started from around 120
grit on a concrete tool. I do not spend effort in timing my grinding
progress. When surface is ready I move to next grit size. I recall spending
around 6 hours actual grinding time getting to 600 grit, and for sure
by this point the offending pits and lopsidedness are gone. I use SiC for
these stages. I add tiles at the 400 grit size. By this point, I won't be
removing much tile surface, and there is plenty of opportunity for the
two surfaces to get matched up perfectly.

We should recall the Sic and most other grits are not of uniformly
exact size. There is a sigmoidal curve of particles from much smaller
to much larger than some average size. From what I remember looking at
the curves, we buy grit according to the size at the midpoint of the
curve. This means that there is a rather smooth transition from one
grit size to the next.

Since I am working very fast systems (F/1.0 to F/3.5), I have much
"deeper" concerns, like polishing and figuring.

;=]


Dominic-Luc Webb

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