|I knew I wanted something around 90:1
ratio. Not much in the scrap box but some cast aluminum.
Didn't think that was the best choice for this job. I found some
cast bearing bronze on Ebay
for a good price. 2.75"od x 1"id when finish
machined. The Shaft that drives the gear for the quill is
.75" I would need an adaptor to mount the gear on the
shaft. An out of spec Shopsmith
1" x 8tpi adaptor was used. I cut off the threaded part,
bored the id to 3/4" and machined part of the 1.375" od to
1" Sorry no PICs of this part. Its the black thing in
the next PIC.
|When the bronze arrived I cut off a 1" slice in the
band saw. Took forever! After machining the 1" bore I
went to test fit the adaptor. What do you know it was a wonderful
"slip fit". ARG!!! Now what? Mounted the
adaptor on an expanding arbor. Then knurled the 1"
shaft. Made for a nice press fit. :) Re-mounted the assembly
faced the end and cleaned up the OD.
|I decided I wanted a pretty heavy worm with good
contact. ACME rod would have probably been better but I didn't
have any and wasn't ready to machine one. I settled on a piece of
3/4" x 10tpi rod out of the pile. I was surprised how well it
machined. The ends are 1/2". A light polish with
emery cloth was needed to clean up the tool marks. I had a
3/4" x 10 die from a previous project. It was run over the
remaining threads to clean them up.
|I decided to use the tap method to cut the teeth on the
gear. Found a 3/4" x 10 tpi pulley tap on Ebay. Price
was good and I would probably make more than one of these worm
gears. A standard length tap will work just as good. In the
PIC the tap is in the chuck supported by the center in the tail
stock. I made an adaptor to fit the 3/4" bore of the gear
blank and thread onto the tool post stud of the compound. The
blank has to spin free but not be sloppy. This was a quick and
dirty method to hold the blank. I need something better in the
|This is how it looks when all set up. Its pretty
simple concept. As the tap spins it starts to cut the teeth and
rotates the blank. The first couple passes looked like crap.
I figured I ruined the blank and would have to start over. At that
point I put more pressure on the tap and things went much better.
Beginners luck :)
|What I ended up with was a well formed tooth pattern in
the gear. I got 84 teeth. Not quite 90 but I knew that
before I started. :) See the notes below for calculating
gear blank size. So far I have not polished or lapped the worm and
gear. It is pretty clean as is.