ATM 13.75" Biscuit cutter

[PFAFF2@delphi.com (Robert C. Pfaff)]

Several ATM's asked about how the 13.75"x1/2" glass was cut.

My setup is almost a copy the setup from Advanced Telescope
Making Techniques Vol 2  More on Trepanning by K. D. Smith.
The cutter consists of 2 disk  of 3/4" thick  particle board nailed
and glue together. It was turned round and to the correct diameter on
a lathe.  (a wood router would do this also). 2 strips of .060"
1.75" steel are fastened around the disk for the cutter. A 1/2 gap
is left between the pieces. This allows the grit to fall in the groove
when cutting. I cut the metal strips with a steel cutting friction
blade on  my table saw. (a carbide cutoff disk would also work).
A large hose clamp was temporary used to hold the strips tight
to the disk until it they were fastened with screws.

A shaft is needed to turn the cutter. I had planned to make a flange
and shaft. In my junk box I found a heavy duty Hi-Fi turntable.
It had a 5/8" x 4" shaft on the bottom. Just bolted it to the
wood disk. With a carbide disk on the table saw I then cut 1/4"
slots every 2" around the steel cutter.

As in the article a wood box with 2" sides was made large enough
to hold the glass. Some newspaper is placed on the bottom, then a piece
of thin window glass and next the glass to be cut. Between the glass 
and the sides of the box plaster is poured. This hold the glass very solid.
The box is clamped to the Mill-Drill or drillpress table.

Next problem. To slow the spindle speed down. On my mill-drill
I removed the spindle idler drive pulley and jerry-rigged
a 1/8 hp 82 rpm gearmotor in its place. This gave me a spindle
speed of 30 rpm. This seem to work well with cutting.

For smaller cutters I think faster speeds could be used.
Also for small cutters I would use thinner or more bendable
strips for a nice wrap about the small disk.

A dam of window putty was placed all the around the cut area
both inside and outside. About an inch on either side of the cut.
Filled with water and plenty of 80 grit. The spindle with the rotating
cutter is lowered onto the glass. A 10 lb weight then atached to the 
spindle handle. Now just stand back and add a little grit and water now and
then.
Watch the spindle depth with the drill depth scale on the mill-drill
or drillpress. I cut 2 disks and each one took about 40 min to do.

Downside,  unlike the core drill in the primary where the hole
was almost straight the sides of the disks have a 5 deg. taper.
Another problem If scratchs are a concern somehow stick
the glass to the window glass. When you cut through
the biscuit of glass will spin with the cutter. Bees wax might work.  

If any of you make it to RTMC I will bring some pictures.
Any unanswered questions just post away.

Happy glass cutting
Bob Pfaff