My used 7x14 surface grinder appears to need a new motor, or maybe just new
bearings. The spindle is belt driven and is currently fitted with GE K163,
1HP, TEFC, 3450 rpm 3-phase motor. The motor is being driven with an
Hitachi L-100 VFD from a 220 VAC single phase line.

With the belts off the motor makes some noise on startup that sounds like it
could be bad bearings. A cup of water sitting on the spindle housing
(spindle belts still removed) has some standing waves at full speed and the
wave amplitude varies with speed. I'm assuming that the motor itself or
perhaps just the motor the bearings should be replaced.

Is the GE motor a good choice for a surface grinder or should I be looking
at other brands? If so, replacement bearings should be pretty cheap. If
the GE motor is wrong for this application, Baldor and Leeson motors with
the same specs above can be had for around $150 on-line.

Also, is it necessary to have a motor specially balanced for a surface
grinder? If so, is this usually specified when the motor is ordered or
should it be done after receipt with the belt pulley in place? Dreisilker
has a service center fairly close to me and would probably be my choice for
balancing should it prove advisable.

TIA, Mike


I don't claim any working knowledge of VFDs. I did look into them a few years
ago when I was hooking up my 3 phase horizontal mill. I eventually decided on
a static phase converter, which meets my needs.

One of the claims made about the VFDs was that the current they supply is not
true 3 phase, but has some harmonics or secondary oscillations which can cause
problems with some older motors. This seems to be rare, but might be your
problem.

Before you dump the motor, you might try driving it with a static or rotary
converter.

John Martin