ATM Worm Wheel Material

[PK6811S@ACAD.DRAKE.EDU]

I saw the recent postings regarding using a tap to cut a worm gear in
aluminum.  I don't have a lathe but thought it might be possible to do
something similar otherwise using two motors placed at right angles.
One motor is fixed and has the tap securely mounted to the shaft.  The
second is on a hinged board so it can be raised and lowered with a jack
screw, the gear blank mounts on this one.

For material I used a circle cutter on a drill press to cut disks from
1/2-inch plywood, they are just the right size to squeeze into  2.5-inch
pvc pipe, and I cut half-inch rings of that to match.  I cut the head off
2-inch 1/4x20 hex-cap screws and screw one into the plywood for an axle.

The setup works fairly well, with both motors running I gently lower the
blank onto the spinning tap to cut a u-groove, then turn the blank motor
off and let the tap do its work.  Amazing how fast the tap spins and how
slowly the blank.

I guess the results would be useable but there is a lot of junk in the
threads that won't come out.  Unlike metal the pvc doesn't chip out - it
hangs on for dear life by the tiniest strings.

How do people clear threads cut in plastic gears?

Paul Kline
pk6811s@acad.drake.edu