Although it worked fine in this application, the 16 tooth worm gear on
my old ATW's threading dial was badly worn. Its supposed to be a worm
gear but this one sort of looks like a plain old spur gear that was worn
in. When I got the lathe, the threading dial was very stiff, it may
have never been oiled. I think this caused the excesive wear on the
In 2005 I got a length of 4140 1 1/4 - 4 acme rod from
Green Bay Manufacturing.
It was fun to turn the shank, nice 20' long stringy chips. I wasn't
paying enough attention to feeds & speeds to get a good finish.
Since I'm using the hob to cut brass I didn't bother trying to put in
top relief or additional hardening. I should have cut the notches
deeper, but these are enough to cut- though slowly.
In Dec 2006 I finally got around to getting the project going again. I
made a mandrel to mount the blank on the dividing head so I could put in
the gashes that the hob will use to spin the blank while it forms the
teeth later on. Feeds & speeds are improving. :)
I got the blank straightened out too. When I put the bore in I'd
forgotten what happens when you try to put in a bore to size with a
twist drill; hole is neither straight or round. So bore it out, solder
in a plug, drill & bore that to diameter. Then cut away the solder
which got all over everything without messing up the dimensions. I
forgot to put strips of aluminum between the chuck jaws and the gear, so
damaged the gear's finish- no big problem, just sloppy.
And then into the dividing head. I computed a 4 degree lead from
Machinery's Handbook, so approximated that by the scale on the dividing
head. I cut the teeth to the depth of the addendum of the final tooth
With the gashes in, I set up a jig to hob the gear.
I finally got around to hobbing the gear;
I recorded an AVI file of it running,
(transcoded to x264, which may help w/ some players)
The lack of relief in the bottom of the thread made finishing slow, and
the 4140 did begin to dull so hardening is in order, even for brass. But
I got decent gear out.
I wasn't confident about drilling the new gear for the taper pin, so put
setscrews in instead. Here is the mounted gear.
And the face of the threading dial after I added some paint on the