On Tue, 14 Dec 2004 23:33:18 -0600, "Mike Henry"
wrote:


"DoN. Nichols" wrote in message
...
In article ,
Mike Henry wrote:
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.

To me, it sounds like a mixture of problems. The standing waves
are most likely from an imperfect balance of the combination of the
motor and the pulley.

The noise during startup could be bad bearings -- or it could be
the vibration from the imbalance passing through resonance with some
structural feature of the grinder.

Since you have a VFD, try starting the motor very slow, and
stepping the speed up a little at a time. If it is a problem with
balance and resonance, you will find one speed at which it is
particularly bad.

When you find this speed, start touching various parts of the
machine to see where you can damp the vibration. If you can't damp it
with pressure anywhere on the machine, then it is more likely to be the
bearings.

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.

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.

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.

snip

If it doesnt slip, and it doesnt flap around like a flag in the wind,
and your water glass test (a very good one btw) is smooth..the belt
is tight enough.

Gunner




"If I'm going to reach out to the the Democrats then I need a third
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"Democrat. In the dictionary it's right after demobilize and right
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-Buddy Jordan 2001