Pinion Gear Pitch?

4gsr said:
The gear hobber hobs or generates the tooth form according to the P.D. needed. The depth of the tooth does not change, just the shape of the tooth. And it's this shape that cannot be cut using involute cutters to cut.
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... so ... a hobber cuts multiple teeth at the same time. Therefore, the spacing one tooth to the other is consistent. Whereas an involute cuts one "fillet" (is the correct term) and thereby 2 opposing halves of a profile at a time the process is potentially less accurate?

I've read about hobbers, never seen one.

Daryl
MN
 
A gear hobber will generate a near perfect gear tooth profile for any given pitch diameter and number of teeth using only one cutter in most cases.

Google Barbra Coleman and Gleason and see what comes up.
 
4gsr said:
It's not a stub tooth form he has or extended tooth depth. It's where they make the pinion OD oversized or undersized, depending where the pitch diameter needs to fall. The gear hobber hobs or generates the tooth form according to the P.D. needed. The depth of the tooth does not change, just the shape of the tooth. And it's this shape that cannot be cut using involute cutters to cut.

Ken
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Ken, trying to get a better understanding of what is being said. Can you elaborate a bit more.

As I understand the shape of the tooth is formed based off the PD, this is the same for any type of gear cutter- shaper, hobber or involute. The reason an involute cutter has a range is due to the size/shape of tooth for the given PD, it changes slightly but that is why you have cutters ranging from 1 - 8 to cover particular sets of teeth. But, you can get an involute gear cutter with a specific tooth count (a bit costly, ~$400. I had to buy one), but very accurate and it will cut 1 - 2 more or less teeth effectively.

I ended up getting a gear shaper over a hobber as it has many more uses, but I will maintain the capability to use involute cutters as they are just as effective. If you are looking for precision, a hobber and shaper is the way to go.

For what Daryl is doing, an involute cutter is great. The things that need to be figured out is the specific tooth form, DP / PA, and if it is a stub, regular or extended depth tooth.

But, I could be missing the point and completely off target. Gears can be so simple yet so confusing.
 
Yeah, if you have the money to spend on a special involute cutter to cut a oversized or undersized pinion, that would be great. But again, it will not give you the proper tooth form as created from hobbing or using a gear shaper. On a oversized pinion gear, the gear tooth at the base of the tooth will be a thinner cross section as that of a pinion tooth cut at the correct pitch diameter. And on a undersized pinion gear, the top of the gear tooth will be thinner than a normal tooth profile would have.
Yeah, this blew my mind when I first saw it. Had a guy who ran gear hobbers and shapers explain this to me years back. And we had two different diameter pinion gears with the same number of teeth as well as the same pitch diameter, too.
 
Another weekend lost doing important things that did not include as much shop time and head scratching as I'd have liked.
I hope all of you will hang on until I get a chance to follow up on the great suggestions all of you have patiently made.

Daryl
MN
 
Daryl, one other thing to check is the DP again. You may have a half size. They are not too common but do exist. I ran into a 5.5 DP in the past, didn't really fit the 5 or the 6DP like it should have. Turned out it was in the middle.
 
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