Gear Hobbing

Way cool @vtcnc.

Did your set come with the drawings?

I don't know what the copywrite laws might be surrounding a set of plans that are no longer available on the free market.

But if there were a way for the drawings to find themselves in my possession, I'd be quite grateful...

I suppose the other way to go about finding plans might be to somehow find/acquire the relevant issues of Model Engineer.
 
MattM said:
I'm interested in gear hobbing. Anyone built a gear hobbing machine.
Click to expand...

Here are a cuple of videos from a guy who made his own hobb and cut his own change gears, and did it on the cheap...

How he made his own hobb:


How he used it (good part starts at ~14:15)

 
This is not exactly gear hobbing in the purest sense of the term more like a kissing cousin. While it is using something like a gear hob to cut teeth, it is not the gear hobbing process unless the work material and the cutter are both rotating at the same time. Also, the cutter couldn't be used as a gear hob because the cutting teeth are essentially straight tooth cutters. A gear hob cutting profile is on a helix.
 
Here is an adaptation that demonstrates gear hobbing. There are something like 8 videos in this series.

 
I have been looking at this kit.
www.martinmodel.com

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
 
vtcnc said:
This is not exactly gear hobbing in the purest sense of the term more like a kissing cousin. While it is using something like a gear hob to cut teeth, it is not the gear hobbing process unless the work material and the cutter are both rotating at the same time. Also, the cutter couldn't be used as a gear hob because the cutting teeth are essentially straight tooth cutters. A gear hob cutting profile is on a helix.
Click to expand...

Understood, and I agree. I thought it was interesting though, what he was able to accomplish "on the cheap" without a true spiral gear hobb and linked process.

I did see another video where they used a spiaral gear hobb, and let the work piece rotate freely - granted they were more chasing a gear they'd repaired, but it worke - the hobb turned the gear while cutting it.
 
I've tried the rack type hobb and it seams to work. Built a depthing tool to hold the gears at the correct spacing and they rotate freely with minimal backlash.
IMG_4442.jpg

Greg
 
ArmyDoc said:
Understood, and I agree. I thought it was interesting though, what he was able to accomplish "on the cheap" without a true spiral gear hobb and linked process.

I did see another video where they used a spiaral gear hobb, and let the work piece rotate freely - granted they were more chasing a gear they'd repaired, but it worke - the hobb turned the gear while cutting it.
Click to expand...
I assumed you knew the difference but thought it worth distinguishing the two methods for clarity. I find the method you linked to interesting as well, because most hobby machinists could achieve gear cutting more easily than gear hobbing using said method. The other "chasing" method you refer has also been called "free hobbing". I'm not sure where the terminology comes from for sure but I wonder if the chasing terminology is used because a hobby machinist could conceivably use a tap to hob a gear. I've heard machinists say, "chasing a thread" and I wonder if that was adopted for "chasing a gear."
 
I don't know how applicable it is, but I fairly often cut gears in my round column mill using a shop-made gear cutting hob.

For anything about 12dp or smaller, it's by far the easiest and quickest method.

 
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
 
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