Recently I had to balance some large couplings in our balance machine. One particular set weight 900 lbs and the run speed was 450 RPM. There was a spec sheet that came with them with this on it: IN/OZ/LB .042 Not sure what this means or if someone wrote it wrong. The customer is a local machine shop and when we questioned them, they don't have a clue and I guess they just didn't want to contact their customer so I was told to balance it like we normally would. This number does not calculate to anything I know so I balanced it to .042 oz/in. which required about a tenth of a gram correction to achieve. I know this is way lower than I should have balanced it and I don't even believe our machine is that accurate. If I ran it twice without any corrections, I can probably get more variation than that. I did the math and for a something at that speed to be .042 oz/in, it would weight a little under 5 lbs. If anyone has any idea what they are specifying, I would appreciate the help.

Thank You,
Ronnie Lynn

I believe they meant OZ/IN per LB. You are wayyyyyy below their spec.

Thanks David,
I knew I was wayyyyyy below any possible spec for that weight at that speed. 4W/N = 8 oz/in and we use 4W/N for 3600 RPM. What you say makes more since, the math for oz/in per lb(.042 * 900) = 37.8 oz/in and G2.5 = 30 oz/in. Just don't understand why speed is not a consideration. Well I guess balance won't be a problem

Thanks,
Ronnie

We got another set of couplings in today that specified .021 IN/OZ/LB. The speed is 900 RPM and weight is 305. With these numbers and applying oz/in per lb I tried to come up with what math they are using and if I base it on speed alone, 18.9 divided by RPM gives the tolerance in oz/in per lb for both sets of couplings. This also converts to a G3.142 using G = 6.015. Does this sound right? And if so, is there an equivalent spec to G3.142?

Thanks,
Ronnie

The units for imbalance should be oz.-in or ounce inches in this system of units, not oz/in, which usually means oz. per in. Actually, balance weights are mass-length; in the U.S. we generally use weight-length.

Maybe they use 18.9 W/N for their imbalance specification?

Thanks Bill, I appreciate you pointing out to me that it should be ounce inches not oz/in. Maybe they do use 18.9 W/N.
Thanks for the input,
Ronnie