Hi Folks,

I'm at it again. I'm working on a plastic "carrier" component to transmit power from an output shaft. I wanted to use a round shaft with two opposed flat sides to do this. I've tested some 3D printed parts and it transmits the torque fine. My problem is that this part is always under a radial load. When I test this the shaft eats up the inside diameter. I've got about 70W at 200rpm with 200N radial force on a ø10mm shaft.

I've designed a similar plastic carrier in which two mini ball-bearings were pressed and the part was placed on a stationary shaft. This time the torque was transmitted via an additional geometry on the part. But the bearings were carrying the same radial load. At the end of the lifetime the bearings no longer have a press fit, but this has not been any real problem.

One problem I have is that the prototype material is PA12 and the final material will be POM acetal resin. So the properies are significantly different. I'm working on doing a realistic test, but I'm wondering if there are fundamentally better options such as a cross-bore and pin instead of the two flat sides. We have sintered steel carriers which mate to the same shaft using a woodruff key and the key is pretty worn at the end of expected lifetime. Trying to go to plastic due to more complex shapes for functionality.

Any tips are greatly appreciated.