Gear Hobbing

[ErichKeane]

I have been looking at this kit.

Gear Hobber Casting Set

The gear hobber is a machine for producing gears by the hobbing process: a rotating gear blank is fed into a gear hob (in the shape of a worm). The maximum capacity is about 4” in diameter, 20 dp (diametrical pitch), 1.25 module down to 1/10” diameter, 120 dp, 0.2 module. The prototype uses...

www.martinmodel.com

Pierre

I'm actually about 90% done with that kit! Down to the last 90%

 

[Bob Neumann]

Thanks for posting Bob
I use the same method to cut small gears with great success. Just thought I'd point out, when you reduce the ends of the hob? to clear larger diameter gears, there should be cutters out there to in-fact remove that material from the gear blank. Though small, that corner you'd be removing will bring you closer to the proper tooth form.

Greg

You're exactly right. I never thought about that before.

The gears I've made have seem to work and mesh pretty well. But you're right I'm potentially missing a little bit of a proper cut.

Thanks for pointing it out.

 

[GHamsz]

I assume he advanced the blank by one tooth for each cut. The ”hobb” (using the term loosely) probably contacted the work piece with 3 maybe 5 cutter teeth. When he rotates the blank one tooth, those teeth that were partially cut will get an additional cut. Let’s assume each tooth is impacted by 3 steps (blank rotations). What you end up with is a piece wise linear approximation of an involute. Granted it’s a crude approximation, but I believe you can improve the accuracy by lowering the cutting tool a small amount, and rotating the blank an amount equal to the amount you dropped the tool. Now cut all teeth with this new position, and you will knock the high spots off the linearly approximated involute from the first pass. You can do this a number of times and get a progressively better curve instead of the crude first pass tooth profile.

This technique uses the same simple setup and “Hobb”, but with a slight tweak in setup and a lot more time, you should be able to produce a nice tooth profile.

Obviously the best approach is to use a Hobb cut on a helix, and have the blank driven in sync with the Hobb, but that setup is non trivial. BTW… I’m looking into designing exactly this which is why I’m looking at what others have done.