Page 330 - Machinery Component Maintenance

312 Machinery Component Maintenance and Repair

Figure 6-38. 180° indexing plot.

rected and biased for subsequent rotors of the same weight and con-
figuration.

Additional indexing and unbalance measurement may uncover a much
reduced residual unbalance, which can again be plotted and pursued
through steps 4-9. This will probably refine both the balance of the rotor
and the bias of the arbor. If additional indexing produces inconsistent
data, the minimum level of repeatability in locating the rotor on the arbor
has been reached. Further improvement in rotor balance is not possible
with this arbor.

Recommended Margins Between Balance and Inspection Tolerances

Quite often the residual unbalance changes (or appears to have done
so) between the time when:

1. the rotor was balanced originally.
2. it is checked for balance by an inspector.
The following factors may contribute to these changes:

Calibration differences between balancing and inspection machines.
Tooling and/or drive errors.