Re: ATM Grinding a 16 inch plate

[Anthony Stillman <atmer@flash.net>]

Rob,

>From the top,


>...back of the glass...flattened by the manufact... is this enough????

Yes


>...f/5 ratio...how much Grit should be used... ??

Silicon Carbide lasts a bit longer against float as compaired to pyrex.
Since I generated my Walters blank I can only guess how much grit it will
take to hog the 20 cubic inches of glass that has to be removed to form an
f/5.  My best guess is 15lbs of 80 grit to hog.   Less than 25 lbs anyway.
You could use 60 grit for a lot of it and save time and grit (maybe 5lbs
60, 5lbs 80), but do the last hours with 80.  Coarse grit does a lot of
sub-surface damage that has to be removed.  This is especially true for
float glass.  I did an hour or so at 60, it made for fast work.  Also,
remember you can rinse and reuse grit.  I do this all the time now.


>...is the technique the same for a 75% tool... or...full length tool..???

For grinding I suggest a full size tool.  For one thing you are going to go
through a lot of tile hogging.   I used up nearly half my tile thickness
with the four or five cubic inches of glass I removed.   For polishing I've
been using a sub-diameter tool.  It has been working just fine.  If I
hadn't built the generator I think I would have tried a hardened steel ring
to hog.  I saw Steve Swazye use this at RTMC a few years back and some on
the list have made mention of this.  It seems to work well.  Also, weight
is important.  I put a 15 lbs weight on top of the tool/mirror when working
it (2 gal bucket).  I used a piece of that stuff that goes under rugs to
keep them from sliding around to keep the bucket from sliding around.

Good luck, and even if you don't keep the list posted on your progress,
I'de still like to hear.


Anthony