"Karl Townsend" wrote in message
...

Watch that video, the hob cutters are trapezoid shape. If using your
method with this cutter you get something that will look like a timing
pulley. if you rotate the blank in unison with the hob set up at an
angle you will get an involute gear shape. the advantage of the hob is
one cutter makes any number of teeth for that gear type.

Actualy that's not right. Run a hob against a part that doesn't move
and it will end mill it. The hob cutters are on a helix.

Here's the article that i used to draw a gear at 50X:
http://www.cartertools.com/involute.html

He talks a bit about a homemade hob at the end.


Just discovered there is an automatic calculator built into CamBam that does
involute gears and timing pulleys. Actually I knew there was a gear
calculator of some kind in the toolkit, but I never looked at it before.
Obviously to use it you need to program backlash compensation in your mill
and/or adjust down your backlash adjustments as close as you can. Still,
with this you can cut them out of plate with a simple 3 axis CNC mill. Cool
beans. Simple profile operation. It even tells you the maximum size end
mill you can use.