Problem- Rumbling sound from the spindle motor area vmc15

[voytek1]

Hi guys,
My machine makes a mysterius rumbling sound from the spindle motor area.

The machine is:

Fadal VMC-15
Model #: 914-15
Year of mfg: 1997
Serial #: 9708670
Baldor Vector Drive, the sticker says: INV-0045
Drive, Baldor FVF1915C; 10HP VMC1
7500 RPM, 10HP, Y/D VMC15

Spindle motor: Baldor 10HP, 3ph
Spec.: 37F71800073 X073 X173
Frame: 215TC,
Volts: 230/460
There is no mechanical transmission on this machine.

Line voltage readings are:
A12 - B12 : 231V
A12 - C12 : 245V
B12 - C12 : 233V
DC readings are confirmed to be 5V, +12V and -12V.
I disconnected the regen. resistor and it reads 13 Ohms.
The temperature in the room where the machine is used is 70 - 85 deg.F.

The machine was bought used six years ago.
I had no problems in running it in any range of speeds or rigid tap from 2-56 to 1/2-13 TPI.
The spindle load during cutting as observed on display rarely exceeds 30 - 35%.
As I use frequently small tools most of the time the spindle will run between 5000 - 6500 RPM @ 15% spindle load.
I mostly cut aluminum, brass or plastics.
I only use pure MOBILMET 404 as coolant and Vactra oil #2 for lubrication.
The machine may run for 20 hrs straight for a day or two and then it may be not used for weeks before the next run.

All the videos I mention in this post and some more info can be found on: http://www.flex-mount.com/fadal/fadal.html

A few weeks ago I noticed a strange rumbling sound while the spindle was decelerating to stop. It happened after running the machine that day only for about 30 min.

When attempting to start the the program, during acceleration the rumbling appeared again and then disappeared before the spindle reached 4000 RPM and the spindle stayed quiet all away to 6000 RPM.

The rumbling was getting louder for each tool change, and always occurring only on deceleration and acceleration.

After a few more minutes the spindle developed hesitation during orientation and during start. (video 02_203.wmv and 03a_212.wmv)

I had to shut down the machine as it was impossible to run it.

After about 2 hours I started the machine again to show to a friend of mine the symptoms and see if he had some suggestions.

To my surprise the machine started without any problems and could be run on any spindle speed without any unusual sound. (video 01_210.wmv)

So I started the job and after about 30 min. the symptoms gradually repeated to exactly what I experienced earlier forcing me to shut down the machine again.

I repeated this cycle a few times and predictably had the same results.

After while I noticed the following regularities:

Shutting down the machine for 20 min. gave me 11 min of work before the symptoms forced me to shut it down.
For 30 min. break I was getting 14 minutes of working time.
For 40 min. break - 17 min. working time.
For 2 hrs break and more - also only 17 min. working time.

In each event the spindle load indicator was climbing from about 25% at the beginning to over 60% at the end of my working time.

In each event the spindle and the motor stayed quiet during it's cutting time at about 5000 RPM without any RPM fluctuation.

Interestingly I noticed that merely turning the main power to the machine ON without turning ON the controller (not pressing the green "CNC Power ON" button) and waiting for about 10 to 15 minutes causes the rumbling problem to show up.

So it looks like it does not matter if the motor is energized or spindle is spinning - the problem will show up after the magical 10 to 15 minutes.

I also noticed that I was able to run the machine on 5000 RPM for about 45 minutes with only one tool without stopping the spindle.

I re-wrote my programs so I would use only one tool for all the pieces without stopping the spindle (I used G4P66000 instead of M1) and then shut down the machine for about 1 hour and then do another operation again using one tool at a time and taking another hour break until I finished the job.

The longest time I used "one tool run" was over 3 hours with 6000 rpm with no unusual sound or vibration however, because I was afraid to damage something during normal stopping of the spindle I shut down the machine by cutting the power using main disconnect.

To my surprise the spindle coasted down to 0 RPM in about 80 seconds without any unusual sound or vibration.

The situation started deteriorating gradually until finally on Aug. 8th I was not able to run the machine at all because:

1 - terrible rumbling on low RPM (two bangs per revolution of the motor) ---See the linked video: 07_244.wmv
2 - The spindle refused to accelerate to higher RPM and the load indicator was fluctuating up and down between 40% and 80% --- ( video: 08_245.wmv)
3 - The spindle was hesitating during start sometimes even kicking backword before it started in the right direction.
4 - The spindle would not orient properly. (video: 06_241.wmv)
5 - The machine runs on low RPM with constant rumble. ----(video 04_213.wmv)

As an additional information:

I used a stethoscope to listen to the motor and spindle bearings rotating the spindle manually and while the spindle was coasting without detecting any abnormality.

At the end of my 3 hours continuous run, using IR thermometer I measured the temperature of the top portion middle section and bottom portion of the motor as well as the spindle. The motor upper section was 95 F. middle section 101 F lower section 96 F. Spindle was 85 F.

I also checked all the components in the space where the Vector drive resides looking for overheated components.
All components and connections were about 85 F. Vector drive was 89 F and the transformer 90 F.

I suspect that what seems as a mechanical noise may really be of an electrical origin such as bad pair of windings in the motor or misenergized winding. Or perhaps the vector drive goes bad. The encoder seems to be OK because I can run the spindle (with bangs) at any very low RPM without change in its speed.

I am completely lost.

Is there any good soul that could help me to solve the mystery?

Again, all the videos I mention in this post and some more info can be found on: http://www.flex-mount.com/fadal/fadal.html



Voytek1

[alex gitzel]

It sounds like a bad motor with some bad windings,or possibly the drive or encoder going out. you should go up to were the electic box is buy the motor and disconnect the wires to the motor and ohm them to ground,there should be no current to ground and if you connect the legs and go leg to leg it should be around .05 to .3 ohms .also listen in back buy the drive to the wye/delta relays and see if they are clicking causing interupted current to the motor.start here and repost results.

[voytek1]

Sorry for the late reply, I had a family emergency.
Thanks Alex for your input.

I checked some stuff and these are the results:

Wye/Delta relays seem to function OK. They are activated after the green CNC Power button is pressed and click decisively.
I also examined all eight contacts and cleaned them to make sure there are no burned spots.

I checked the motor windings for shorts. No shorts.
The resistance between legs on the motor is 0.3 Ohm for each pair of legs.

I disconnected and took apart the resolver on the top of the motor. It is clean. Just in case I wiped the disk with the lint free cloth (the one used in cleaning fiber optic components) as well as the detector.
I put it back together.
This did not change the machine behavior.

I also managed to run some more tests (described below) to look for some regularities.

Test 1:
I turned the machine on and set the spindle speed (in MD) to 4000 RPM.
I activated the spindle (M3) and the motor started with some rumbling which quickly disappeared on it's way to 4000 RPM.
I increased the speed all away to 5500 RPM without any unusual noise.
The spindle was then left running for about 3 minutes.
I shut the motor down with M5 and the rumbling sound appeared right before the stop.
The spindle stopped in about 3 seconds.

Test 2:
I turned the machine on and set the spindle speed (in MD) to 2500 RPM.
I activated the spindle (M3) and the motor started with much more rumbling than before which again quickly disappeared on it's way to 2500 RPM.
I started manually reducing the spindle speed slowly and the rumbling began at about 1800 RPM.
The more I decreased the speed the louder the rumbling became.
At about 1550 RPM it became unbearable.
Then as I was increasing the spindle speed gradually the rumbling gradually was disappearing until I reached almost 1900 RPM at which speed the rumbling was gone.
I repeated the same procedure without stopping the motor about a dozen of times. Every time with exactly the same results.

Test 3:
I turned the machine on and set the spindle speed (in MD) to 150 RPM.
I activated the spindle (M3) and the motor failed to start right away.
It kept kicking on for several times but finally started with distinct bumping sound and stayed that way on 150 RPM for about 5 minutes then the machine went into emergency stop by tripping the motor overload relay.
I think the message was Error #8.
I shut down the machine.
I reset the relay (White button see new picture 264b.jpg) and I noticed that two terminals (T1 and T2) on that relay were very hot and one (T3) barely worm. Actually the hot part was the center portion of the relay.

After these tests the spindle had difficulty to both: start and stop decisively.

I shut down the machine and after about 10 minutes I was again able to start the motor and run it at 2500 RPM. With same results as in test #2.
This time however the spindle had difficulty to start. (See new video: Post2.wmv)

I looked at the explanation of an Error #8. Where is the spindle magnet sensor?

I also checked all terminals inside the vector drive for loose wires and visually checked for any burned components.

The new video and some more pictures can be found at: http://www.flex-mount.com/fadal/fadal.html

[smittys800]

What is the possability that a magnet is coming loose in the spindle motor itself?

[scadvice]

Originally Posted by smittys800 What is the possability that a magnet is coming loose in the spindle motor itself?

??? Sorry smittys there are no magnets in the spindle motor. Voytex the spindle magnet sensor sets just under the fan on top of the motor. (I think that what your asking for) Hummm... maybe I the one having the senior moment!
Steve

[voytek1]

Originally Posted by scadvice ??? Sorry smittys there are no magnets in the spindle motor. Voytex the spindle magnet sensor sets just under the fan on top of the motor. (I think that what your asking for) Hummm... maybe I the one having the senior moment! Steve

Right, there are no magnets in the spindle motor.
I also do not see any magnets on the top of the motor under the fan ( or I am just to old ?).
I believe the spindle rotation sensor is the one marked by me as Sensor #2 on the second set of pictures at http://www.flex-mount.com/fadal/fadal.html
The magnet is right under it.
I am assuming that the spindle rotation sensor works just fine since it causes Error #8 when the spindle (or motor) refuses to start after M3.

Any other suggestions?

Voytek

[Neal]

voytek1--
The error #8 is indicating a problem with the spindle orientation circuit. It could be the Hall effects sensor looking at the embedded magnet in the spindle pulley. This is the usual cause of the error. Also the cable down to the 1010 spindle controller card or possibly, but highly unusual, the 101 controller card itself. An error of #10 would indicate the spindle motor encoder having an issue.
To verify this:
1. At Enter next command enter DI
2. enter DS
3. this will display some sensors and switches ion the screen.
4. Look at the center column and the top item-ORIENTSP
5. This is orientation sensor
6. manually rotate the spindle 360 degrees slowly several times.
7. Each time the magnet passes under the hall switch the display should turn to a value of 1 and then return to 0 as the magnet moves awaay.
8. If this does not change state or is erratic in changing state then you have verified the that circuit is having an issue.
9. To remove the switch display from the screen press the letter X.

Hope this helps clear things up.

Neal

[scadvice]

When doing what Neal suggest, clean the area around the hall sensor (Shaft Mag. and sensor area) Sometimgs goo and chips can get in there. I've seen a few machines where the little can like cover is missing or loose, allowing this to happen. Also a loose connection. Sometimes people mickymouse an after market auto air filter up there and that can push on the sensor and cause problems.
Steve

[voytek1]

I verified that the ORIENTSP goes from 0 to 1 while magnet passes under the sensor.

I think that because the motor refuses to start rotating the spindle on time,
the sensor properly reports it to the controller and the machine goes to the emergency stop with Error #8.
I am in the process of running extra tests to look for more specific events that would occur in predictable manner.
I will post it as soon as I get it done.
I will also update the material on the my web page.
Meanwhile, thanks guys for your involvement in trying to solve this puzzle.

Voytek

[alex gitzel]

I think the spindle drive may be the problem.check the voltage going to the motor while running and then while it is acting up see if it is jumping around,if the drive is bad the noise can sound just as bad as a bad bearing.I did have an encoder also cause similar issues before especialy the us digital one you have ,the new ones are sealed one pc. units.they are around $300 or so.and are the cheapest part to try first,and in my opinion are just plain a good idea to replace i have seen so many issues caused by the old ones during my time in field service that they are one of the first things i try with an oddball issue like this.you can just run the cable on the outside to test with,if you get one be aware 2 wires have changed( the thick black goes to shield,and the white goes to blue).you also can check the control input voltage to the drive,check pins 4+6 on the 6 pin molex for dc voltage,between 0 and 10 vdc check for steady voltage.there is also the possiblity of a bad motor bearing showing up under load.if you have another fadal now would be a good time to swap the drives and see if it follows.

[voytek1]

I checked the voltage between pin 6 and 4 on molex connector.( See: molex.jpg)
The voltage is steady on each speed regardless if the motor rumbles or not.

Maintenance manual (page 271) says :

“ On a standard machine a 1.3 volt DC signal will result in a speed of about 300 RPM in low range. ”

I set each speed with Sxxx, so I was in the low range and these are my readings:
150 RPM: ------- 0.21V
200 RPM: -------0.27V
300 RPM: ------- 0.41V
500 RPM: ------- 0.68V
950 RPM: -------1.3V
2500 RPM: ------3.38V
What am I missing?

Another thing I noticed was that the rumbling noise on the low range disappears at about 2000 RPM of the motor sped but on the high range disappears at about 3400 RPM of the motor speed.

This would mean, if my logic is right, that it could not be of a mechanical origin (like a bearing) from the motor which should stay at the same RPM of the motor regardless of the low or high range of setting. (See. Video: Low_High.wmv)

I disconnected all the wires at the motor from lines T1, T2, T3, as well as from lines 4, 5 and 6.
I measured a resistance and these are the results:
Between the wires that were connected to the line T1, T2 and T3 all readings show an open circuit
Testing to the ground shows an open circuit.

Between the wires that were connected to 4, 5, and 6 all three readings show an open circuit.
Testing them to the ground also shows open circuit.

Between wires that were connected to 4 and T1: 0.16 Ohm.
Between wires that were connected to 5 and T2: 0.16 Ohm.
Between wires that were connected to 6 and T3: 0.16 Ohm.

And finally between 6-2, 6-1, 5-3, 5-1, 4-3 and 4-2 shows an open circuit

During each measurement I manually rotated the motor shaft 360 Deg. to make sure that the readings do not change. No change detected.

[voytek1]

My apologies. I made a mistake in taking the measurements of the resistance between the motor leads.
I just edited my last post to give corrected readings.
Sorry I guess I am just getting old.