I am a intern who was tasked with finding the correct amount to mill off (in an angle) of a bearing cage (basically an annulus with gaps in it to hold the balls or rollers) to bring it back into balance.

Basically the only parameters that I have are the Outer Diameter, Inner Diameter, minimum unbalance allowed (0 gmm), maximum unbalance allowed, the density of the material, max milling depth for that part, and two unbalance values on the ring at two different degree locations.

The original thought process to find the degrees to mill off was using the midpoint between the OD (outer diameter) and ID, and the unbalance, find the unbalance mass ( mass = unbalance/(OD/2+ID/2) ). After that we use that mass and the density provided to find volume. After finding volume, we find the surface area from volume/milling depth, and then we find that as a percent of the total sa, and do % * 360 to find the angle to remove.

I have basically implemented the same concept, with minor changes on how instead of just assuming the mass is summed up the midpoint between the ID and OD, I calculate for the centroid of the part to be milled off, and keep iterating downwards after doing the initial calculation till I am sure that the unbalance to be removed in g * the distance between the centroid and the center of the annulus (bearing cage) is within an appropriate range (less than the max appropriate unbalance).

I am getting values close to the old values, but my main issue is that people in the past complained that the old values were not always right, so I was wondering are there any parameters that I should output that might increase the accuracy, or are there any other ways to calculate that you would consider?

A parameter I was considering adding was a midpoint between the two max unbalances, where it would be the further of the two midpoints between the two unbalances, and then telling them to mill from there as that would be the most likely to regulate the unbalance.

Any suggestions on parameters I could consider adding to make the milling process more accurate, or is there a way that I can improve the accuracy of the calculations?

  • $\begingroup$ Rotating devices are generally spun to determine what needs to be done to achieve balance. The loads on the device you spin it on can assist, and there are even specialized devices that track the part and report against a datum. Old fashioned method might be to add masses to balance it first, and then calculate the removal. $\endgroup$
    – Abel
    Mar 14 at 0:47
  • $\begingroup$ I'd hire a millwright or equivalent trained in balancing equipment, not an engineer. acoem.us/blog/other-topics/… $\endgroup$
    – Tiger Guy
    Mar 14 at 15:05


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