"DoN. Nichols" wrote in message
...
In article ,
Mike Henry wrote:
snip
Well, I tried your suggestions and am a bit perplexed. The gradual ramp
up
revealed that the vibration (or rather, wave amplitude) was worst at about
51 Hz and somewhat smoother at 60 Hz. Applying force at various locations
didn't seem to make a difference until I started to fiddle with the motor
mount. The mount has a rigid plate cantilevered off the back of the
column
to which a hinged plate is attached. The motor mounts to the bottom of
the
hinged plate (motor is upside down) and there is a spring-loaded bolt to
adjust the angle of the hinge, and presumably the belt tension between the
motor and spindle pulleys. The standing waves all but disappeared as
soon
as the adjusting bolt was, er, adjusted. No amount of re-fiddling could
bring the standing waves back.

Hmm ... perhaps the belt was too loose at first, and flapping
around at the speed in question. Can you find a new resonance point?

Or perhaps there was just enough give to make for resonance at
that speed, and clamping a weight on the plate would shift the resonance
point.

I've no clue on what changed unless maybe the grease in the motor bearings
suddenly re-arranged itself for more complete lubrication. The grinder was
bought used from a dealer and I don't know how long it sat before it arrived
here. It's had about 10 hours of run time since arrival.

Put the belts back on and cranked up the grinder to 60 Hz - no standing
waves. A test grind with some 12L14 and a blue 5sG46-IVS Norton wheel
produced passable results.

It sounds good to me.

Tried to call KO Lee today but got put on automated hold and gave up
before
a live voice responded. I'll try them tomorrow and see what they say
about
motors. I also need to find out what sort of tension the belts are
supposed
to have.

FWIW -- the manual for my Sanford grinder, which uses a flat
rubber belt says the following:

"Belt tension should be such that the belt between pulleys may
be compressed to within one inch of touching. This is rather
loose, and should be so."

I don't know how this may apply to your machine, as it is a
different size and a different manufacturer.

KO Lee tells me that this motor (GE K163) is the one that they installed on
surface grinders (although they now specify 2 HP instead of the 1 HP on
mine), that they do not specify any special sort of balancing and that the
(2) belts should be adjusted so that there is about 1/8" "give" when pressed
from the side. The tension was a lot less in my tests the other night so
I'll play with the tension a bit to see how that affects things.

The tech support guy seemed pressed for time and was not interested in any
kind of detailed answers, so I'm not feeling any better informed than
before.

Mike