Re: [ATM] Started Hogging

["Bob May" <rmay@nethere.com>]

A bit complex and complicated but usable.  I assume that you're
doing something in the 15" range for that depth.  You're final
depth for the first hogging is a good one as you will be wanting
to not go too far and mess up by having to remove a lot from the
edges.  I usually go about that far myself with the iron tool.
This allows me to constantly decrease the ROC as I go through the
coarse grits and keep the center from getting unground relative
to the edges.
Personally, I just embed the tiles in the cement and not worry
about epoxy and this approachy is a lot easier to do.  The tiles
won't fall out of the cement if they are fully encapsulated by
the cement.  Tiles at the edge that are not held at the outer
edge do tend to fall out as they aren't fully held in by the
cement so don't bother to try to get tiles all the way to the
edge of the tool when you cast it.  The cement will also be nice
and hard so the edges of the mirror will be ground down if you
are worried about that.  I don't even worry about older grit
staying on the tool as the first wet of the finer grit will
remove them as you go.  Just make sure that any holes in the
cement are filled in and there will be no place for the grit to
go and hide for a while.
BTW, my favorite hogging tool has been a pipe end cap, preferably
with a hole in the end of it so the air has a place to excape.  A
pipe flange, one of those things used to hold a piece of pipe to
a floor or wall also works well, especially for larger mirrors.
The hardest thing is at the end of hogging in getting an
approximate spherical shape to the hole.
I'll also note that the large grits usually don't last too long
as they break up rather rapidly but they are indeed, as you have
seen, removing a fair bit of material.  As you get to the finer
grits, they will last longer and turn a lighter gray before
stoppiong their work.  Resist the temptation of grinding too long
with the finer grits as the glass load will only keep the grit
from doing its work.
Also, get away from the 60 grit quickly as it makes for deep
chips which will take a long time to get out of the glass.  I'd
probalby do the last ten thousandths of an inch of hogging with
the 80 grit for this reason.
Good Luck and Have Fun!
Bob May
Due to the large volume of SPAM thaat I'm getting, add an open
square bracket to the subject line or my spam filter will reject
your post~
rmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net
Replace the obvious words with the proper character.

_______________________________________________
ATM mailing list http://www.atmlist.net/