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View Full Version : bevel drive gear- floating or fixed?



darryl
09-23-2015, 08:04 PM
Getting my right angle gear drive project up to speed- now I'm wondering if I should fix the small gear to the shaft, or let it remain loose on the splines. In the original application it floats loose, and it doesn't appear to have a tendency to move either in or out. I'm using the back side of the teeth, meaning that I'm running it backwards to the original rotation direction to take advantage of the unworn surfaces on the gear teeth- also because the motor is run in to this 'backwards' rotation direction. I've been playing with the meshing, and it is a little quieter in the 'normal' direction for the gears, but not by a lot. There was some damage done to the teeth on the big gear in the forward direction, but the reverse gear is good, and that's what I'm using. The small gear is slightly damaged, but not on the face of the teeth- just a few nicks at the edges.

Perhaps I've answered part of my own question- perhaps I should run the gears in the direction they are worn in for, and reverse the motor rotation to suit. The small gear should likely want to push back on the splines to some extent, and there is a bearing surface on the back of the gear to take this load- but this will be grease filled and not oil filled as in the original application. I'd rather take advantage of the ball bearing on the motor shaft to handle any axial forces, and this means that the gear needs something on the motor shaft to back up against. It would be easier if I just JB weld it in place.

In this motor the brushes have a slight offset, so I presume it's optimized for one direction of rotation. I could make a new end bell and position the brushes opposite to what they are now, or just make them 90 degrees to the commutator like every other dc permag motor I've seen. I don't mind making a new end bell, as I would provide a heat sink for the brushes. Currently they are in a cast bakelite end bell which provides little to no heat sinking, which I'm not too fond of.

It matters little to me which direction I have the output shaft spinning as I can arrange the mounting of the assembly to suit- one thing which would matter is the handedness of the threads that would be used to hold the saw blade on. I'd rather use the normal thread as I would use a normal tap and readily available bolts. This does coincide with the normal running direction for the gears, so perhaps these two plusses are greater than the one minus, the need to reverse the direction of the motor.

Back on whether to JB the small gear to the shaft, or let it float free- pretty much every helical bevel gear assembly I've seen leaves the gear floating. Maybe I should simply provide a machined washer on the motor shaft for the gear to back up to.