From: Mark Holm 
To: gboutin{at}infinichron.com, atm{at}shore.net
Reply-To: Mark Holm 


Gerald,

Others have given some good advice, but nobody has come out with the blunt
statement yet, so I will.

On an 8-inch blank, at 500 grit, 1/8 teaspoon is considerably too much.  I'm not
quite sure in any standard measurement system how much is enough.  I tend to use
too much, and I am pretty sure I am not using as much as 1/8 teaspoon.

At any particular grit size there will be a surprisingly large range of pit
sizes.  This is especially true of Silicon Carbide.  Part of it comes from
variation in grit size within a particular grade, part of it just comes
from the
random nature of the grinding process.  The pit sizes are more uniform when
you switch to Aluminum Oxide, especially if you use the good stuff like
Microgrit. I think the AO in W-B kits is good.

If you have one nasty pit that is clearly larger than anything else and
doesn't want to go away, it is probably left from rough grinding.  If you
are pretty sure it is the only one, it may not be worth worrying about. 
The problem is the
needle in a haystack situation.  A ground surface can hide a lot of pits. 
If you have one you know about, it is a good bet there are others.

Cut back on the amount of grit you are using and do another dozen wets.  If
the pit is still there, you will have to make the hard decision: go on and
risk more
pits showing up when you polish. or go back.  Don't let one pit bother you
to much though.  Except for the eagle eyed inspectors at the coater, no one
will ever know it is there except you, and as you enjoy the good views from
your scope, you will come to forget about it too.

I think it must have been Russell Porter who wrote this story in ATM1.

        A farmer went to a blacksmith to buy an ax.  The ax had an
        excellent bright edge, but the rest of the head was covered
        with pits.  The farmer asked the blacksmith to grind the whole
        ax head as bright as the edge.  The blacksmith agreed, on the
        condition that the farmer turn the grindstone.  The farmer
        began turning the stone, and the blacksmith leaned the ax head
        hard against the stone.  Sparks flew.  After a time the farmer
        asked how the work was progressing.  The blacksmith answered,
        "There are still some pits, keep turning".  A while longer and
        the now red and winded farmer asked again.  "Keep going", replied
        the smith, "There are still pits".  At this the farmer said,
        "That is enough.  I think I like a speckled ax best".


Mark Holm
mdholm{at}telerama.com

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