Gear hobbing in a lathe using a tap - video

[Frank S]

I've done this many ties but I found out early on that it was best to start the tooth cut near the bottom of the tapered end when making these gears that way as the depth of cut progresses and the teeth are beginning to take shape you do not experience the tooth movement around the perimeter. Cutting a radius grove prior to cutting the teeth is also advisable especially when the thickness of the disk is near to the same as the diameter of the tap.

[NortonDommi]

A spiral flute tap helps too.