Specifying two balance grades for the same part

[geesamand]

I have a component that is machine balanced and then mounted on an overhung shaft. To leave room for straightness error of the overhung shaft, we balance to a single-plane imbalance that's very good (<G2.5), but because of the conical shape a true two-plane imbalance is not achievable to this level. As it's a cast part, I am uncomfortable with ignoring the two-plane imbalance quality, so I want to specify a rough control over the couple unbalance component.

I can think of two ways to handle this, and I'd like to confirm if they are technically correct and likely to be understood:
1) Specify single plane unbalance limit (oz-in, <G2.5). Declare two balance planes locations and specify another unbalance limit (oz-in, G16?) on each of those two planes.
2) Specify single plane unbalance limit (oz-in, <G2.5). Specify limit of couple unbalance component (oz-in^2).

The second method is simpler but I'm not sure it's technically sound or well understood by balancing vendors. What's the best engineering practice?

 

[mmamini]

if you can send drawing from your part, It might be helpful to talk about your problem.

the permissible residual unbalance must be calculated according to ISO 1940-1. this value is calculated for center of gravity and if you want to have a dynamic two plane balance, you must recalculate the permissible values in each plane individually using translation methods.
but if the CG is located between balancing planes, you can divide the permissible unbalance values by 2.

but! the balancing quality Grade is defined a value for whole rotating component. you can not talk about balancing grade for each plane. you can only say that if you want to have for example the G1 balancing grade, the minimum permissible unbalance value on each plane must be less than something specified.