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