I'm designing my first plastic press fit component with metal shaft. I've gone through the calculations however a senior engineer has been telling me the part won't fail in the way I think it is.

The press fit purpose is: Hold the press fit plastic part in XYZ with an additional tool that locks the part in Z and would assist in Z axis angular rotation.
After the part is dropped down in Z and other equipment moves, the part is rotated 60 to 180 degrees. Very rarely rotated after this only for potential repairs...

The concerns I have are

1.) Press fit interference - The interference shows the safety factor for the interference will cause plastic yielding. Senior engineer is telling me that's normal and it just means the part plasticly deforms and shears against the metal shaft. He told me there is no concern for this "failure" in the equations and you'll find it works experimentally.

2.) Rotation failure - The part is rotated on occasion. Yes the part deforms plasticly and will sit around the shaft but when it's rotated ~60 degrees(shaft is locked in angular rotation, plastic hub rotates only), couldn't the press fit fail from shear forces from this small rotation and loosen the Z angular rotation? I don't quite know how to account for this with any equations other than experimental evidence using the sigma min and maxes of the plastic part.

3.) Rotation and press fit forces - I've simulated the rotation forces and it matches to the yielding point predicted in my calculations. I've also experimentally press fit another material over another pin and calculated the values and it also nearly matches my predicted press fit forces so I'm confident on these two subjects.


Other questions I have on the subject matter:

How does surface roughness affect the part?

How to accurately include creep stress relaxation and temperature effects combined with creep stress to predict overall outcome of this part? or is it usually done experimentally?