From: "Bob May" 
To: "atmlist" 
Reply-To: "Bob May" 


Sounds like you still have about that .007" to go with the nickel
tool.  I assume that that tool is pretty well rounded and is producing a
good spherical surface.
Since you have a near full sized tool, you should be getting a decent
sphere for 80 grit with no problem and since it is a metal tool, it won't
be changing its radius by very much as you grind so do the TOT and keep the
grit working on the mirror.
I tend to just use the 2" end cap and with that, I tell the guys doing
the grinding (often repeatedly) that where you grind is where the glass is
ground away, thus if you have a high ring, a bit of grinding on that ring
area will quickly bring it down.
Sounds like you are going along just fine.  If you really want to, you can
cast a tile tool but I'd wait for a little bit longer until the whole
surface is ground to where it needs to be and then make the tool. I also
prefer to put the tiles in the tool rather than gluing them on later as I
then have control over the amount of any grooves on the tool surface (only
put a single shallow groove if the guy is having trouble with the tool
vacuum locking in the finer grits) and so forth. The initial grinding is
usually going to take as long as the polishing of the surface with pads. 
Once you have the initial curved surface, the going down through the grits
is also going to take about as long if you insure that the surface is fully
ground out on each level, and chasing pits for a little bit in the larger
grits.
Bob May
http://nav.to/bobmay
bobmay{at}nethere.com
NEW! http://bobmay.astronomy.net

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