Fanuc 6M spindle VFD motor noise and high load

Folks,

I have an issue with the spindle drive and motor on my Yamaguchi YMV-60 mill. The machine has sat for a year and a half or more unpowered. Recently I got it fired up. I ran the spindle slow, 100 rpm at first. I let it run for a couple minutes, then stopped it for a minute or so, then started it again. After a few minutes of that I ran it at 500 rpm, then 1000. Everything seemed to be going well. Then I got brave. I started it back up at 1000 then kicked it up to 2000. It ran for a few seconds, then made a sort of a squawk sound and now the motor makes noise. It not tremendously loud, but noticeable. Definitely not good as the load meter is higher now than before the noise. I noticed that when I was running it at 100 rpm before the noise the spindle speed was not very steady. It would speed up/slow down and the load meter fluctuated between 5% and nearly zero. Now the load meter is at least 10% @ 100 rpm with the noise. I ran the spindle (with no tool holder) on and off for around 20 minutes or so give or take. I don't have the drive information right handy. I will be able to add that to this post later tonight.

I have taken the belts off the motor, so I know that it is not spindle bearings. I checked the resistance between all 3 windings. They're about the same as far as my meter could tell, 0.7 ohms. No winding was shorted to ground. I did find something interesting, however. While running at 500 rpm the voltage across the two phases was 50 volts, two other legs was about 100 volts. I would think they should be a lot closer to each other than that. I checked the voltage at the main disconnect of the machine and got 234-242 volts. I have this running on a phase converter that I have used previously with my Mazak lathe with T1 control.

I investigated a bit further. I am quite certain it is in the drive or motor. The link below is a short video of it running. The first half is 100 rpm, then I sped it up to 500 rpm.

https://plus.google.com/104092800892...ts/AThiM2Chh7R

Picture of the motor:

Attachment 244238

I am hoping someone can educate me on these drives so that I can trouble shoot the failure. Perhaps the SCR's have faiiled, but what cause them to fail?

Thanks for your help,
Aaron

sounds like your spindle bearing. quick test. with your spindle at a free state. turn it by hand. if it spins freely. not a bearing.. if you spin it and it drags.. bad bearing... another way is turn spindle to like 1200 rpms. while spindle is going turn the machine off. the spindle should spin on its own and slowly come to a stop.. but I don't recommend this option at this point..

Sorry. I guess I should have read the whole thing.. Idk then...

some drives dont like phase converters...we had our own little rebuild shop in a small single phase building, first machine i rebuilt wouldnt run on a converter, had to go rent a big diesel generator for testing...i'd verify power if possible first... ac fanuc spindles achilles heel seems to be the built in mag sensor- they demag over time, wont run...usually if dead, they just squeal and run real slow at 150% current...closing the gap ofen gets a few more months out of them, but... ive had rear motor bearings spin too, if the shaft starts wobbling, the mag sensor gap varying will screw them up too...still guessing it just might not have liked the converter.

Is this mag sensor inside the motor? How do I check if it's providing the proper output? Could that cause the leg voltages to be as unbalanced as they are?

What gets me is that it was running great for a few minutes, then just started squealing like you flipped a switch. It's didn't start low and get progressively worse. Rather it just started doing it. The rest of the machine seems to be running just fine. I could cut chips with it if it wasn't for this problem. What things can I check on the drive itself to make sure it's ok?

Thanks for your knowledge!

i dont know these drives real well, but weve had a lot of 'issues' over the years...i think if it was your sensor, it would be pegging the loadmeter- but a loose rear bearing can make them act really weird. a lot of these drives had a dozen little clear fuses along the right edge by the FETs, if one or two blew(possibly because of the phase converter?) it might run at low power/errattic/imbalanced... but replacing might just misfire again, eventually blowing one of the big transistor modules. if you have a big old three phase motor, might suggest wiring it into your phase converter output, start/let run before booting machine- the iron/windings kinda act like a rotating transformer, will help stabilize the 3 phase, we got ours to run that way, but still not right...was only like a 7.5 horse motor, a bigger one mighta helped more (if you got power to start it)...on a real 3 phase generator it was less buzzy/smooth...
i have a cnc bridgeport in the garage with a fanuc zero i run on 120 volts- transformer bucks to 170 volts, and on the old 6047 servos, if you feed 170~180 into A-1-2 terminals (jump 1-2 together on one leg) they run fine at reduced output...can run 3 axis simultaneous at 100 ipm with spindle on, at 120/15 amps :)

never had much luck fooling spindle drives though