Erich's Benchtop Gear Hobber Project

[ErichKeane]

Yes, quite a few of them...I searched on gear cutter 20DP. For a set of 8, $65 plus $5 shipping. So I was inaccurate.

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That's not gear hobbers though, those are approximated gear cutters. Gear hobbers look like these : https://www.ebay.com/itm/3636309326...H8d09NDpOAvztPK9HzlDkD-8QSOleH4gaAvMXEALw_wcB

A single cutter will cut ALL numbers of teeth exactly, rather than approximately, since they use the rotation of the gear to cut involutes correctly.

The intent of a hobbing machine is to use these gear hobbers to cut the gears "correctly" and in a reasonably automated way.

 

[Winegrower]

I see. Sorry to get you excited. These cutters are what would make Brino’s spur gears. You’re in a different league!

 

[ErichKeane]

I see. Sorry to get you excited. These cutters are what would make Brino’s spur gears. You’re in a different league!

Ah, I see what you mean! Yeah, I considered just making gears that way to 'start off' the hobber (I have a couple of those cutters as well), but personally feared they would result in me being less motivated to make a whole set with the hobber if I had a couple of aluminum ones already Part of the idea is that the plastic ones would be 'good enough to get going, but suspicious enough that I wouldn't consider them part of a full set of gears' to motivate me to cut all the aluminum ones on the hobber!

One of the nice parts of this hobber though, is once you set the angle and power feed right, you can leave it to its own devices for a while and let it cut a couple at time! I intend to leave the spindle long enough to let me cut 3 gears at a time, so I can make myself a set of 2-of-each (useful due to the length of the gear train!), and perhaps end up with an extra set to pass onto someone.

The DOWNSIDE of course to any hobber is the cost of the hob cutters, but it is only 1 per PA/DP combo, and I figure I can self-standardize on the size I got for a while if need-be.

 

[f350ca]

Wonder if you could make them.
I make a cheat one, basically a hob without the spiral. The centre set of teeth cut the tooth while the ones above and below relieve the adjacent teeth. Work fine one small gears,
I cut the tooth form at 14 1/2 pressure angle, basically an acme thread, by plunging straight in. You should be able to determine the pitch and cut the rack form then for the teeth as I do on the mill.





Made from drill rod then hardened, cutting bronze I don't bother to temper them.

Greg

 

[ErichKeane]

Wonder if you could make them.
I make a cheat one, basically a hob without the spiral. The centre set of teeth cut the tooth while the ones above and below relieve the adjacent teeth. Work fine one small gears,
I cut the tooth form at 14 1/2 pressure angle, basically an acme thread, by plunging straight in. You should be able to determine the pitch and cut the rack form then for the teeth as I do on the mill.

View attachment 428042

View attachment 428043

Made from drill rod then hardened, cutting bronze I don't bother to temper them.

Greg

Yeah, some folks do home-made gear hobs that way. This project was a little too much work already, so having to make my own hob was a bridge too far

 

[ErichKeane]

Ok, so I got some work done! A while back, I was able to get the parts all cleaned up and spray-primed, so first task was the color coat. Through the afternoon, I sprayed 2 coats, which will hopefully be all I need to do. I noticed all the tapped/drilled holes are pretty messy wiht paint/paint-stripper/overspray, so I'll likely need to clean those up as I re-assemble:



Next, I did some quick thumb nuts, which were just a turn to diameter, drill/tap 5/8-18, knurl, and part. Hardest part was fixing the threads after parting them off



These nuts will be used to tighten things on the lead screw collar part that I'm making next. The plans dont have a thickness, so I thought 200 thou was a good look. Worst case, they are easy enough to re-make. I ended up using some hot-rolled I had around the shop for those and the next part.

Onto the collars! These will end up holding the dial/gears on the leadscrew, and interface with one side of the thrust bearing. This will be more obvious when I assemble these. First, I found some scrap A36 from some knurling practice, and turned the OD down to .800.





Next, turned and polished the smaller diameter down to .625.



Then, a quick single-point. The threads look ugly in this picture, but they were actually quite nice cleaned up.



Finally, drilled, and reamed for 3/8" to fit on the lead screw extensions:



Flipped around, and faced to length:



FINALLY, I had to broach the inside. I'll eventually have to cut an external keyway as well, but I want to see how keep the larger broach for the 5/8" makes it, so I can cut it to fit. One thing I DID have a problem with: The little 1-ton arbor press I was given at one point is REALLY not up to the task! It can only JUST handle the 1/8"-A broach length, and even then I couldn't use the bottom plate, I had to drill a hole in some aluminum plate to even be able to use it.

I'm going to have to come up with a different solution with the bigger broach unfortunately, which I was hoping I wouldn't have to do.

In the end, it 'worked' well enough:

 

[rwm]

You could broach it on your lathe maybe? How long is the keyway?

 

[ErichKeane]

You could broach it on your lathe maybe? How long is the keyway?

The larger keys are 5/8 diameter, and 1/8" wide. Though, if I was going to cut those, I would probably just do it in the shaper.

I got the broaches because these are pretty tiny.

 

[dkemppai]

The little 1-ton arbor press I was given at one point is REALLY not up to the task! It can only JUST handle the 1/8"-A broach length, and even then I couldn't use the bottom plate, I had to drill a hole in some aluminum plate to even be able to use it.

Just a thought...

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Things about this are so much better than the discount tool supplier designs with bottle jack. Being a small bench top unit, it gets used more than I though it would.

 

[ErichKeane]

Just a thought...

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Things about this are so much better than the discount tool supplier designs with bottle jack. Being a small bench top unit, it gets used more than I though it would.

Thats neat! Though quite expensive to ship. I'll have to see if there is anywhere local that sells stuff like that.