PM-1236 motor issue

tino_ale

Active User
Registered
Joined
May 20, 2014
Messages
59
Hi guys,

I'm still in the process of properly setting up my PM-1236 but I suspect I have something wrong with my motor.

I noticed the machine would run quite loud and has some strong vibrations. I machined a titanium bead that came out as you see below : huge pattern is transfered to the finish.

nx7ubd.jpg


I proceeded to check the spindle bearing preload :
- I did the "one finger spin" test, I get about 1 turn of free spining, that's supposed to be right. The chuck is not that free to spin.
- I chucked a 40mm rod in the 3-jaw chuck, grabbed with both hands that bar 400mm away from the chuck. DI positionned above the centerline, tip on the spindle cam lock area. Vertically I get about 0.0003" in the down direction; a little less around 0.0002 up. That makes sense, as it is easier for me tu push down than pull up. So 0.0005" overall. Not sure how much is acceptable but doesn't sound that much.

So I rulled out a sloppy spindle.

I then removed the belts and ran the motor alone. Left the sheave on. This is what I found :
- the noise and vibration is mostly still here, so the issue is narrowed at the motor+sheave level
- by hand, it is very easy to turn, no noticeable grit feeling, smooth (but not entirely silent ?? maybe normal, I speculate I hear the balls running in the bearing)
- when powered on, the loud humming is back along with the vibration
- I feel vibration on the motor body itself. The lathe yes but not that much. The stand, a lot. The stand acts like a resonator of some kind.
- as soon as I stop the motor power, the humming and the vibration stops eventhough it is still spinning fast. Then the motor continue to turn freely, for about 5-10 seconds. During that time, I only hear what I think is the bearings running, but the machine is silent otherwise and vibration free.

conclusion : the issue is at the motor level and only there when the motor is powered on. That pretty much rules out a defective bearing or an imbalanced rotor.

Here is a video of the sound.

Did any of you have had that kind of issue ? What is the fix ? I have a metric machine in 220V, could it be related ?
I speculate the issue is electrical but I do not know that for a fact.

Any advise welcome !
Thanks !

nx7ubd.jpg
 
I think you have found the problem, but I can't tell you exactly what is causing it. Based on your excellent troubleshooting, it must be electrical and internal to the motor.

The only fix I can think of is to replace the motor, or isolate the motor with rubber mounts.
 
Thank you.

Actually another PM1236 owner has heard my video and says the free spinning sound (right after I shut the motor power off) doesn't sound normal to him.
If you hear close enough, there is a noise even in the free spinning phase indeed.

So it seems I may have ruled out the motor bearing and/or balance a little too fast.

Anyhow, I cannot run the lathe with so much vibration from the motor. It is a brand new machine, I'd rather have a normally running motor than a lemon mounted on rubber pads.

There's another thing : I wonder if the motor is not running too hot. When I did the break-in procedure, the 3 jaw chuck was on but empty. I ran the lathe for 5 min on each speed, forward and reverse. So it took a while. I then noticed the shop was getting warmer, I touched the motor and almost burned myself. Pulled an IR thermometer, found the motor body was 90°C (almost 200°F). That sounds really hot for a machine that is running with no actual cutting load. Oil levels are spot on and oil type is good. I don't know what is going on.

I have enquired Matt about that motor issue and waiting on his reply.

Any thoughts are welcome
 
Last edited:
Yes, given the 200 degree temp unplug it before something melts and you get an electrical zap. Water boils at 212 degrees.
 
You probably already thought of this, but aren't yall on 220v 50 Hz? Is it a 60 Hz motor? Don't know if it would make a difference or not, just a thought. The bead looks cool with those lines in it, though!
 
90C does seem way to hot. I wonder if the motor has a dead winding? Bad run capacitor? Bad (sticking) centrifugal switch?
 
Always told if you cannot lay your hand on it its to hot. Some times cannot lay your hand there on motor very long but can lay your hand on it . Should be a temp rise for the motor above the room temp? Bottom line you need new motor.
 
I agree... there is something wrong with the motor.

The hum sounds like an electrical issue... as thought the motor is fighting with itself. And the temp is WAAAY too hot, even if you were dogging the lathe doing cuts too deep.
Might try running the motor (with the belt removed) for about 1/2 hour continuously... then take its temp again. A motor running with NO load, should not heat up at all... that would be a significant clue.

Not sure if you have any motor shops in your area... we have them around me and they could tell if I took the motor to them... or you Emailed them the video.
Might find a motor forum and post the video to see what you get back.

Contact Matt... he has always been straight with me.

And let us know what you find.

THX

GA
 
As mentioned, most of the EU is 230v 50 Hz. This will cause the motor speed to be less and in some cases some motor derating, but unlikely to be the cause of the issues mentioned. Although it sounds like a replacement motor would be appropriate as opposed to repair,, changing to a 3 phase inverter motor with a VFD would probably be a better option. This would afford you a wider speed range and better surface finish.
 
Doesn't sound right. I'd say you have a stuck centrifugal switch, but I think I hear it operating when you turn the motor off and it spins down. Have you made sure it's wired correctly?
 
Back
Top