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# Crowing a small spline

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## Crowing a small spline

(OP)
I'm designing a quill shaft for a small turbine engine that is powering a generator. The max torque is 478 inch pounds and the spline is an 18 tooth 32/64 pitch spline with a pitch dia of .5625 inches. Both the turbine and the generator are on squeeze film dampers and could (at the maximum defection in opposite directions) have a misalignment of .010 inches. The quill shaft is just over 6 inches long and this results in a maximum misalignment of right at a tenth of a degree. The question is, should this quill shaft spline be crowned? The spline depth is a half an inch, which with a flexible spline gives me a surface stress of 9594 psi according to the Machinery's calculation. Given the relatively small size of the spline and the small misalignment, the amount of crowning is going to be pretty small in order to keep the surface stress under control. The operating speed is 44k rpm, but the life required for this is relatively short as it is a concept demonstrator. Machinery's recommends crowning for misalignment's of greater than one degree, but given the higher speed here the question is, should this be crowned and if so how much?
If I put in sufficient crowning to handle a one tenth of a degree misalignment over a half the spline length I come up with a crowning of about .00045 inches and a crown radius of 71.6 inches. That's not much crowning in this small a spline. The surface stress goes up to about 16ksi, which is higher than desired also.

I'm pretty sure Terry can answer this one looking at a previous thread on crowning.

Thanks,

Manny

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