Awright you mechanical engineering and math types, More on the high speed spindle, boys and girls. This boy calculated the bursting speed of the ER collet nuts he want to spin up. It is much higher than the speed I will be spinning the things. However, the nut and holder will need to restrain the collet. Doing a very conservative calculation on the centrifugal force (I know, centrifugal force is imaginary) acting on one segment of the ER collet spinning at
32000 rpm I get the result of 176 Lbf acting on .05 square inches which equates to 3520 PSI. There are 6 of these segments if that makes any difference, though I don't think so. Not for the hoop stress calcs that is. Anyway, using 3520 PSI as internal pressure, a mean diameter of .635 and a wall thickness of .109 I get a hoop stress of 10253 PSI. As near as I can tell this is well below the maximum stress for mild steel and the nut is certainly stronger than mild steel. I have not yet figured out how much the nut will tend to expand and I don't know how, exactly, to go about figuring out what the bending stresses are at the 12 places where the edges of the collet segments contact the holder. I suspect this is something not to worry about since the space between the segments is so small. So are my conclusions close to correct so far? Please feel free to point out any errors. Thanks, Eric- posted
9 years ago