Finishing gear teeth

[Rich_Carlstedt]

What Earl said can work very well. We did that at work. We had a machine with high speed metal forming of sheet metal and the gears ran at 4,000 RPM or so and factory made gears yielded horrendous noise, in fact you could not stand it.
So all purchased gears were placed on a plate with 3 studs , 2 were bearings (w/seals) and the third had a motor driven stud to fit the size bore of the gears (and key) Drop in the gears and brush the teeth with abrasive (valve Grinding compound or Emery)adjust the middle gear to have a slight drag with the other two and turn on the motor , Don't run too fast or the abrasive gets thrown off. Every 10 minutes, put on some abrasive and tighten the setting every 20 and in an hour you should have some nice running gears. We were told that having 3 with the same diameter is not the best, as it can set up a synchronous imbalance, so every 20, the machinist would lift a gear and turn it 10 or 20 teeth.
You could spring load the center gear, but then only those gears will work together as you really reform the teeth to a perfect mating condition. Our gears were 4140HT to start, so CI may be a bit easier ?
Rich

[earlgo]

If you could make a setup with adjustable center distances, you could run the gears together with lapping compound in the teeth and in a crude sort of way, lap them smooth.
Just another thought.
--earlgo

After I wrote this it reminded me of an interview for an engineering position that I had in the last century. At a consulting engineering firm one of their projects was to make a gearbox with precision gears a pair of which were bevel gears. They were proposing to lap the gears by running them on parallel shafts, and I was asked what I thought of the procedure. There were drawings already prepared. I looked at the interviewer and was thinking was this a setup or what. Apparently ALMOST everyone knows that true bevel gears are conics and the teeth are tapered being smaller toward the center. For that reason they cannot be run on parallel shafts. Maybe these guys had some sort of modified bevel gear whose teeth were not tapered, or perhaps the teeth were so short that it didn't affect the outcome. On the other hand it was a precision assembly and should have been made according to the rules. As I recall, I patiently explained the conical bevel gear configuration, instead of laughing out loud.
I was offered the job, but declined.
--earlgo