Using Hobs without a Hobbing Machine

Well I just did a quick sketch and it is true that if the blank is small enough you will only cut a single "facet" and the tooth form is straight sided, though the number of teeth is going to be very small! So probably not of practical interest.

That could only be possible if each stroke indexed one tooth, which isn't how it works. The tooth form is generated by moving the table and rotating the blank a tiny amount between strokes, not a full 1-tooth index.

I need to make 2 gears with 5/16" Circular Pitch, one 13T one 50T and 4 gears with 1/4" Circular Pitch, one each at 12T, 21T, 53T & 62T so the hob idea is certainly of interest as I would only need to make 2 hobs and they would only be needed once.

I already have a normal cutter for the 1/4" CP gear.

The only thing that worries me is the amount of sideways force on my ancient vertical worktop mill although that could be reduced by gashing the spaces first.

Many thanks for all the replies, they really do help.

Brian

Edited By Brian H on 02/01/2019 18:18:08

No, you just index 1 tooth and don't move the hob, as Neils box of gears confirms

You get a better curved profile if both are moved like a Sunderland machine, as JS's post part way down this page shows

Edited By JasonB on 02/01/2019 18:39:37

I think we are at crossed purposes, I am referring to the setup in Phil's pics - his dad's setup for Myford changewheels.

Got you, Phil's setup does move the rorary table a very small amount for each stroke of the tool, only difference between his and a Sunderland is that the gear (table) moves along the rack rather than the rack moving along the gear's axis.