Fine downfeed phase4: Hobbing the worm gear

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After reading about how other guys have tried to hob a gear blank, I decided that I'd give it a shot. I've also seen folks use their lathe to do this, but I figured it was worth trying on the mill. I had to build a fixture to hold the blank during hobbing, so here is what I came up with.

 

It took a bit of machine work to make the shaft that fits snugly into the center hole of my 3 jaw chuck. There are probably more accurate ways to do this, but I'm satisfied with how this is turning out.

 

All lined up and ready to hob...er, I mean cut. Who ever came up with hob anyway? I can't remember what tap I used because it has been a few years since I built this, but you can probably get away with any size that will fit with the threaded rod you'll use to drive the worm.

 

After a few light passes to get the teeth started, the tap self-indexes the gear blank and an increasing pressure on the x axis hobs the teeth of the worm.

 

All hobbed and ready for cleanup.

 

After some touchup with the file, it is ready to try out.