[ATM] (not) grinding with diamond

[Douglas S Angle <Douglas.S.Angle@can.dupont.com>]

I've built a curve generator using a cheap diamond blade, similar to 
what's described on Dan Cassaro's page http://home.comcast.net/~cassarole/ 
and Peter Smith's http://www.users.bigpond.com/pjifl/page16.html.  It 
started off well, but after a while the blade just stopped cutting.  I've 
tried a few things differently, but now I'm stumped.

The project is a 16" f/6.  The glass is mounted on a rotary table built 
from a worm gear reduction drive.  The tile cutting diamond blade is 
backed by an old gear for rigidity, which is welded to a 1" shaft, which 
is turned by a belt off a drill press pulley.  The whole thing is held 
together by a wooden frame.  The glass rotates about 30 RPM, and the blade 
about 200rpm.  The shaft is held by wooden blocks, oiled for friction. 
Pressure on the blade is just from the weight of the pulley, shaft and 
gear, which amounts to a few pounds.  Not exactly a milling machine, but 
it does seem to work.  The glass rotates, the diamond wheel rotates, it 
makes scratching noises, in fact it seems to do everything I expect but 
cut the glass.  Which was kind of the point to start with.

I started with a 10" tile cutting blade, mounted to a wooden disk, such 
that the wood presses only on the rim, and the mounting bolts pull the 
center up a little.  The shaft is tilted to the correct angle, and garden 
hose provides water for cooling and dust control.  (if you are considering 
trying this search the archives for diamond generation and read all the 
safety warnings about silica dust first!)  The curve starts in the center, 
and went well until there was a concave section about 5" in diameter. 
Things then went progressively slower until it basically stopped grinding 
at about 8".  There seems to be some wear on the blade just inside the 
diamond rim.  At that point I added the wooden backing disc, but no 
change.

I then bought a new blade that seemed more suited to the task from shars 
http://www.shars.com/Online_catalog.htm?sec=126&lang=1033  pg 82   cat# 
D1A1-2234.  I would have preferred a cup wheel, but didn't find one big 
enough for the job.  The diamond is actually thicker than the aluminum 
part of the blade, so it protrudes a bit.  There is a little lip on the 
inside of the diamond edge, which I've trimmed off as much as I can. 
There's no wear patterns on the metal part of the blade.

I mounted this blade, and got essentially the same results. After an hour, 
it hasn't even taken out the scratches from previous work.  The references 
above talk about hogging in minutes, but I've had this running about 4 
hours in total now. 

Any suggestions, particularly ones that don't involve buying another 
diamond wheel? 

Thanks
-Doug

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