View Full Version : Spindle motor problems

02-11-2010, 08:10 PM
Hi All,
I have a problem in that my cnc mill keeps tripping the main consumer unit in the workshop. The fault is intermittent and happens at any time when in use - sometimes when I start a cut and sometimes quite a way into a programme. Also when on no load - spindle only running - it can run for ages with no problem or cut out within minutes or, as the other day, within a few seconds, so it's not that the motor or whatever is getting hot. At other times it will complete the programme with no fault.
The machine was originally a Warco WM16 single phase machine - useless as it was - and has had a complete upgrade on ballscrews/stepper drivers, etc. Everything works well now apart from this intermittent fault on the spindle.
We have changed the spindle motor, spindle driver board, checked all wiring for shorting out, have bypassed the E-stop (works only on the driver boards cutout - not on mains isolation to machine) to check out any faults there. As I said, the machine has been upgraded and runs very nicely apart from this problem.
After changing all the above, it has successfully run for a total of around 12 hours of actual machining time and then suddenly had the "popping" problem again. Sometimes stops with a loud "pop" (sound coming from around the head area where there are also the spindle driver board and "filter" board) and at others just stops and each time trips out the main consumer unit.
The only thing I haven't changed yet is the filter board. I have no idea what this does but have been told it has rectifiers, etc on it.
I am not into electronics (what I know on these can be written on a pinhead) so I'm now frustratingly asking for any help on this problem that I can get.
If anyone has come across this problem, or can offer any ideas as for a cure, please can you help?



02-11-2010, 10:07 PM
I would check the filter unit as it is designed to short out high frequency feed back up the mains and a componenet could be shorting to earth(capacitor)

02-11-2010, 10:13 PM
I had a similar problem with my milling machine. Are you absolutely sure it's the machine not something else causing the fusing? It turned out mine was tripping because the outside light was faulty, so every time the cat walked past it...

02-11-2010, 11:35 PM
are there brushes in the motor, if so check they're not on their last legs.

02-11-2010, 11:46 PM
Hi Peter,
The filter is the only thing on the machine that hasn't been changed. Usually if there is anything with a faulty board, they show physical sigs of failing, but this looks perfect - as new.
I will have to see if I can get a filter board for this machine - can't go back to Warco as we are in a bit of a battle with them over the useless machine they had sold me. Do you - or anyone else reading this thread - have any idea where I could find a board to replace this one?
Regards, GeoffB

02-11-2010, 11:51 PM
No it is the machine that's doing the tripping - everything else that runs off the circuit is fine and has been for all time that they have been run from the ring main. I have two different circuits/rings in the workshop on differentr trips in the main consumer unit, but this problem trips the main trip, not just the circuit trip. It is only when this machine is running - the lathe or compressor or whatever else has no problem.

02-11-2010, 11:58 PM
The motor is brand new - literally 12-14 operating hours old. We had this problem with the old motor fitted - and that had only a few running hours on the clock as the machine had not been run due to it's many mechanical and stepper problems. The old motor had been checked as OK by a motor rewinding company and it had new brushes fitted. When we had the problem, we fitted a new motor, but that had the same problem - changing the driver board and partially isolating the E-Stop seemed to cure the problem for some 12 operating hours, then it started happening all over again - there is no arcing from the motor and it runs just fine - until the "popping" of the trip.

03-11-2010, 07:08 PM
Just a thought but does the main board have a elcb fitted as its not normal to trip the main unit and not the local mcb.
If it is a elcb then that is more likely that it is the filter!!
Id you have an ammeter I would try to measure any earth leakage present.
(just be careful how you measure it though)

03-11-2010, 07:30 PM
Hello Peter,
Thanks, but I'm not sure on this one. We have been thinking on this and the motor is starting to sound ropey as it did with the original motor, which has set us thinking back to the motor itself.
Anyway, since last night the engineer has come back to me and said that the filter is nothing to do with the spindle driver board. The feed to the driver board is seperate - to check this, we took out the inline fuse to the filter and the only difference that it made was that the tacho readout on the front of the machine didn't work, which is not a problem as the speed is controlled from the computer. The motor ran up just the same. so the filter is nothing to do with the motor.
Now the motor only runs for around 15-20 secs before it pops and as I said, it sounds like a two stroke on misfire!.
I checked in the top of the motor whilst it was running and it's like a firework display in there - which points to possible brushes problem (as i2i suggested earlier) which I couldn't believe as the motor is a brand new unit - only 12-14 hours on the clock - that was why we were looking for other causes. I will check the brushes in the morning.
The only thing that is different on this machine from its original set up (in the spindle motor area), is that we are running it the opposite direction as we have a toothed belt drive to achieve 1 to 1 as opposed to 1.85: that was on original gearing to get the spindle speed up to higher revs for the small cutters we are using. As we've taken out the gears, consequently the motor runs "backwards".
As far as we knew, DC motors run in either direction - but maybe we're worng and it is this that's causing problems and taking out the brushes? Does anyone know?

03-11-2010, 07:43 PM
Some motors are designed to run in one direction only and do not take kindly to the reverse direction ie the brushes have bed in in one way and could stick if run in the opposite.
A heavily sparking brush will cause the motor to consume more current due to the negative resistance region of the arc caused at the commutator, also bad for the life of the motor.
Try it running in the opposite direction and see how long it stays running.

03-11-2010, 08:13 PM
I had thought about this, but was assured that they will run both directions. Will check the brushes in the morning and try the motor in "reverse" (in its designated direction according to the arrow on the motor). If that's the case then we will have to run 1:1 gears by the looks of it.

07-11-2010, 07:25 PM
Hello All,
To update on this problem, it appears that the original thought of the "filter" board as the problem turned out not to be. It wasn't connected in any way to the spindle motor supply or control.
So it appeared to be down to the motor itself - what was actually happening to cause the problem, I've still no idea.
I removed the brushes and they were very bad - worn quite a bit (that in itself was really surprising, as I have had motors on machines that are many years old, without having brush replacements) and burned/chipped on the mating face. One brush had the connecting wire literally fall out - a little burnt on the brush end - whilst I was inspecting it.
I removed the motor - as I said earlier, a brand new unit only 12-14 op hours old - stripped, cleaned and inspected it for obvious faults - the comm was fine and cleaned up OK (and before anyone says - NO I did not use any abrasives on the comm - just the scouring side of a washing up pad - these work absolutely fine) and the motor appeared perfect.
I fitted some new brushes and rebuilt the motor.
I have re-run the motor at around 2000 rpm - in the direction that it is arrowed - for around half an hour, to gently bed in the brushes and then upped the speed, running it in both forward and reverse directions. It sounds and runs OK at the moment and has now done around an hour's operational running since.
I did check the brushes after about half an hours running and they looked OK.
Just awaiting the new gears for the unit now, so that we can run the motor in the correct direction. Clutching at straws, maybe, but it is all that we can come up with. It has been suggested that we fit a "choke" to the motor supply to smooth out the DC, which I am looking into.
I'll keep you posted on further developments.