Our specifications would require that residual soft-foot is no more than 0.002 inch on a motor of any size. This specification is based on measurement using a dial indicator at each foot rather than use of the soft-foot function included with the laser alignment equipment, which can give a false low reading.
0.002 mils is a good number to shoot for. That is what EPRI recommends.
It is important to talk a little about the method/technique for measuring.
I would say from worst to best the three methods are:
1 - Loosen one foot at a time and check movement at the coupling.
2 - Loosen one foot at a time and check movement at the top of the motor foot.
3 - Use a feeler gage inserted under all 4 corners while the motor sits on it's base before tightening any feet.
IEEE (841) and NEMA (MG1) standards for new motors have specs similar to #3 that apply to the motor itself (not the motor as it sits on the base) which are measured with the motor sitting on A tool grade B flat surface. The specs mentioned in these standards are considerably more than 0.002" which seems paradoxical given that these are new motors under ideal base conditions (granite base). But NEMA specifies very specific aspects of feeler gage technique
"feeler gage of required tolerance shall not penetrate a circle centered on bolthole with diameter = 1 inch or 3xBolthole diameter, whichever is greater."
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