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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 gear.





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 profile.





With the gashes in, I set up a jig to hob the gear.





February 2007

I finally got around to hobbing the gear;




I recorded an AVI file of it running,

hobbing-gear.avi

(transcoded to x264, which may help w/ some players) hobbing-gear.mp4



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 background.



;;; eof