"Peter Grey" wrote in message
ink.net...
Hi all,

I just got my Gorton mill up and running and I'm experiencing some
weirdness
with the knee motor which powers the table cross feed through a gearbox
(three ranges with four speeds in each range). Both the 1/3 HP knee motor
and the 1 HP spindle drive motor are three phase and I'm using a 4HP motor
as RPC.

With the gearbox disengaged (so there's no load or relatively little load
on
the motor), every four or five seconds the motor loses a little RPM (as if
a
load were being placed on it) and then recovers. With the gearbox
engaged,
but not the table, the RPM changes are more pronounced. With the table
engaged, although the RPM drops aren't always severe, the table and motor
can stop completely. When I disengage the table the motor takes a second
or
two, but then it'll come up to speed again. It doesn't sound particularly
stressed during these incidents. The motor is running warm to the touch
after five minutes or so.

The main motor and the RPC motor run fine during these periods, with no
change in their speed or apparent load, so it appears to be isolated to
the
knee motor. Since it does it with very little load, I'm assuming that the
problem is in the motor itself or something that "feeds" it. There's also
no consistency to where this occurs if the table is in motion. IOW, it
doesn't seem to be binding anywhere. There's no one spot or gear
combination where this is worse, other than being worse when I use higher
table feed speeds, which I'm assuming means higher load. I suppose I
could
pull the motor and see if it does the same thing sitting on the bench not
even turning the input shaft of the gear box, but with the thing turning
1,700 RPM, there's nothing in the gearbox that would cause resistance only
every four to five seconds.

Is this typical of something? Bad motor? Bad electrical thing-a-ma-bob
that feeds the motor? It's a cool old motor. Can these be rebuilt cost
effectively?

Thanks,

Peter

There's not that much to break in a small 3-phase induction motor. I'm with
the OP that there's something in your gearbox -- but if dismounting the
motor will not only verify it's operation but also let you dink with the
gearbox to find a problem, that's not a bad thing.