Milled gear vs. Shaped Gear?

[CarbideBob]

. And yes, I freely admit to being a GearSnob™.

This gets more than a like. He was also a totally great customer in the past.
If I need a special gear and tight tolerance this is the guy I will go to first for price or advice.

 

[Bill D]

I was under the impression that a gear hobber kind of polishes the metal as it skives off a slice at a time. Same idea as burnishing.
Bill D

 

[EmGo]

I was under the impression that a gear hobber kind of polishes the metal as it skives off a slice at a time. Same idea as burnishing.

Absolutely not.

 

[memphisjed]

I am no gear snob; I wish I had the ability to be one.

So that said stupid question.
Would gear axle/bearing/placement need to be of same precision as gears themselves?

 

[Mark Rand]

Would gear axle/bearing/placement need to be of same precision as gears themselves?

Yes, in the sense that TIR and looseness of the shaft is the same as TIR and looseness of the gear.

 

[stephen thomas]

What all the parameters are trying to attain is perfect rolling motion.
So yes, if the shape is wrong or the center distance off, "a bit?"; then an "element?" of sliding is introduced.

For what applications or under what circumstances (speed, load, mostly; + lube) does it begin to matter?
Alternately, how much is too much for a given app?

 

[EmGo]

So yes, if the shape is wrong or the center distance off, "some?"; then an "element?" of sliding is introduced.

With involute teeth there is always sliding. In the beginning of the mesh there is "approach action" where the teeth are sliding against each other. In the middle area it's mostly rolling, then towards the end there is "recess action" when the teeth are sliding away from each other. In cases of high production it is common to optimize the teeth to maximize recess action and minimize approach action. For example, back when cars were rear drive, the hypoids were very much designed that way, which is why the rear end would how like a banshee in reverse but be quiet going forward.

Would gear axle/bearing/placement need to be of same precision as gears themselves?

You've been listening to Illinois Tool Works They printed an entire pamphlet explaining how most gear failures were actually bearing failures. Of course they built gear tools, not bearings, so maybe they were prejudiced but still, they had a point If you don't hold them stable, where they belong and parallel to each other or at the proper angle, then you've already shot yourself in the foot, they can't perform at the level they were designed for.

Actually, involutes are a little bit forgiving of center distance imperfections, which is one reason they are popular and common. Cycloids, like in clock gears, have less friction but they are very un forgiving of center distance variation. So they aren't as good for most cases.

But center distance tolerance can't make up for out of parallel or feeble support or any of the other shitty bearing problems. Gears transmit motion, if the foundation is not solid then they can't do a good job.

 

[eKretz]

Right. That's just common sense. A major bearing failure can result in skew to the point where it's just like you bored a hole crooked or off-location, etc. A system (such as a gearbox) is only as good as all the parts in the system added together. If everything is correct, it will sing. If not: crunch, munch and heavy wear.