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
7 years ago