Spindle requiring too much hp to turn

[Wren]

We are having a problem with our machine that I hoped to get some help from the people here on.

The machine is a Hurco VMX 24 with 10,000 rpm 40 taper spindle. Spindle hp is listed as 10/12.5.

The problem we are having is that the spindle acts like it does not have enough hp available as it should. Turning on a 1/2" endmill to 10,000 rpm takes 30-45 seconds just to spin up and another 30-45 seconds to spin down with the spindle load meter showing "overload" the entire time. This seems like an unreasonable length of time based on my experience with other machines.

When the machine is cutting it does not seem to have enough horsepower available either. For a standard pocketing operation, using a quality 3 flute aluminum end mill in 6061, I can only go about .200" deep and 25 ipm and the machine is screaming the whole time. I can even hear the spindle bog down with big radial engagements of the tool.

Also, the chip auger will trip its breaker soon after being turned on if there are many chips to push at all.

I have talked with Hurco several times and all of the spindle acceleration and deceleration parameters are correct. They think that the machine sounds like it is starved for power and I think so too but I cannot find it.

The power into the machine at L1-L2, L2-L3, and L1-L3 is always 235V-240V. We have run the machine on the three phase power that comes into the shop as well as on a Phase Perfect digital phase converter. The results are always the same. Electricians have come in and set up monitors to watch the power over several days and not found any problems.


Does anyone have any ideas or has anyone seen anything similar to this? I am at a loss and getting ready to call in the service guys.


Thank you.

 

[SND]

Perhaps something fried in the VFD that still lets it sorta run but way low on power? or something fried in the motor itself, it must be getting hotter than usual?
I'd check as many connections as I can to be sure they're tight, and also for burn marks, anything suspicious.
Even my little 2412 is up to 8K and back to zero in no more than a second each way.

With that said, on hurco's website it shows the VMX24 has a 12hp/1min peak, which sounds to me like a 5hp/cont motor eh? seems to me it should at least have a 7.5hp/cont (fanuc robodrill's are 5hp/cont and they say 14.75hp peak) so you do the math...

 

[Bobw]

Personally I wouldn't trust an electrician to know shit about electricity, they run wires and conduit, hook red to red and black to black. They seldom ever have to deal with actual flow of electricity.

I would start by measuring the voltage to the machine while the spindle is spinning up. If it takes 45 seconds, even the shittiest multi meter should give you a reading.

My thoughts, something is loose or not properly connected somewhere. Do you have undersized wire going to machine?

Do you by chance have some aluminum wire somewhere in the mix that hasn't been tightened down lately.

Did some asshole do a bad wire splice and hide it in some conduit, might be able to find something like that with a small infrared temp reader.

Do you have a breaker or disconnect box that is shot?

If you're getting slow chip conveyor and spindle problems, is your transformer about to puke? Do you have a loose or corroded contact going to, or maybe from the transformer in the machine.

Lots of stupid little things that you should be able to narrow down pretty fast.

 

[Wren]

Personally I wouldn't trust an electrician to know shit about electricity, they run wires and conduit, hook red to red and black to black. They seldom ever have to deal with actual flow of electricity.

I would start by measuring the voltage to the machine while the spindle is spinning up. If it takes 45 seconds, even the shittiest multi meter should give you a reading.

I measured the voltage on the different legs several times in many different configurations with two different multi-meters. Spinning up, spinnning down, in the cut, turning in air, etc. it stayed very constant on each leg each time.

I also thought I might be dropping a leg under load but if I am, I cannot find it.

My thoughts, something is loose or not properly connected somewhere. Do you have undersized wire going to machine?

I will go over every connection, good idea. I will also check all wire size and wiring. What would be the correct size for it?

Do you by chance have some aluminum wire somewhere in the mix that hasn't been tightened down lately.

I doubt it, the building has been refurbished recently. I will do everything I can to check.

Did some asshole do a bad wire splice and hide it in some conduit, might be able to find something like that with a small infrared temp reader.

I will try to run completely new wire on a temporary basis and see if that solves my problem.

Do you have a breaker or disconnect box that is shot?

If you're getting slow chip conveyor and spindle problems, is your transformer about to puke? Do you have a loose or corroded contact going to, or maybe from the transformer in the machine.

We have actually tried the machine on several different circuits. A 480V stepped down to 240V and on a regular 240V 3 phase circuit. The problem is the same either way.

Lots of stupid little things that you should be able to narrow down pretty fast.

I really hope so. Thank you for the advice.

 

[Captdave]

I would be checking the amperage draw on the motor at each leg while in operation. Is the motor getting excessively warm by checking with an inferred thermometer? Is there any type of brake that could be engaged?

 

[3t3d]

Can you measure the DC bus voltage?
Does it have a DC bus?

 

[mike_kilroy]

2 different motors whimpy..... anything else messed up? anything else on the machine TO mess up?

did they make this machine as a 240/380v machine? sounds like it is set up for 380v instead of 240.... measure the motor currents on both motors and post them with all motor nameplate data and we all can compare and see if perhaps they are indeed voltage starved....

 

[PaulT]

When the machine is cutting it does not seem to have enough horsepower available either. For a standard pocketing operation, using a quality 3 flute aluminum end mill in 6061, I can only go about .200" deep and 25 ipm and the machine is screaming the whole time. I can even hear the spindle bog down with big radial engagements of the tool.

Something is definitely wrong, using the quick and dirty horsepower calculation below with a typical HP factor of .3 for 6061 aluminum shows you are only putting about .75 HP into that cut.

HP = WOC x DOC x IPM x HP factor = .5 x .2 x 25 x .3 = 0.75 HP

Keep in mind that you will never get full rated HP into a cut due to HP overratings and HP drop off at higher RPM's, but you should be able to get 3HP or so into a cut at that RPM, so something is really wrong, perhaps the spindle drive is faulty.

It sounds like you have established that your input power is good, next I'd put a voltmeter directly on the motor input leads to verify that the motor is getting full voltage.

Paul T.
Power Technology

 

[Wren]

Here is some more background information on the machine. Sorry, I had this in my first post and then lost that post and failed to put it in my new one:

The machine is ~10 years old. It was used for about 4 years and then put into storage for another 4 years. It was stored in an air-conditioned building, but not completely prepped for storage. Mostly it had the coolant removed and was then unhooked from power.

The guys here started using it again a couple of years ago but they did not know anything was wrong with the hp required.

Also, all of my measurements were on the voltage at the switch, not the voltage on the wires directly to the motor. I will try to measure directly to the motor as soon as possible.

Perhaps something fried in the VFD that still lets it sorta run but way low on power? or something fried in the motor itself, it must be getting hotter than usual?
I'd check as many connections as I can to be sure they're tight, and also for burn marks, anything suspicious.
Even my little 2412 is up to 8K and back to zero in no more than a second each way.

With that said, on hurco's website it shows the VMX24 has a 12hp/1min peak, which sounds to me like a 5hp/cont motor eh? seems to me it should at least have a 7.5hp/cont (fanuc robodrill's are 5hp/cont and they say 14.75hp peak) so you do the math...

Is there a way that I could check the VFD?

I am not sure how hot it should be getting. It has been this way as long as I have been here.

I would be checking the amperage draw on the motor at each leg while in operation. Is the motor getting excessively warm by checking with an inferred thermometer? Is there any type of brake that could be engaged?

I did check this and it was very consistent across all three legs.

I am going on memory, but I think that it drew 25A on each leg as it was spinning up and then 11A on each leg maintaining 10,000 rpm. Those measurements were again on the wire after the main on/off switch and into the machine.

I will check again tomorrow when the electrician gets back with the clamp-on meter.

Can you measure the DC bus voltage?
Does it have a DC bus?

I am not sure if it does or does not.

2 different motors whimpy..... anything else messed up? anything else on the machine TO mess up?

did they make this machine as a 240/380v machine? sounds like it is set up for 380v instead of 240.... measure the motor currents on both motors and post them with all motor nameplate data and we all can compare and see if perhaps they are indeed voltage starved....

The machine is still very capable of making good parts. Rigid tapping works well. As best i can tell, it is just fine except for the motors not having enough power.

The spindle motor definitely says 230V on the name plate, as does the Hurco specific plate on the cabinet.

The wiring to the machine appears to be 6 AWG wiring. Is that adequate?

 

[Bobw]

Off the wall one here, since this machine sat in storage for a long time.

Are your motors spinning freely?

 

[ipmmiller]

curious,how does it run in reverse? brushes in spec. length?

 

[CarbideBob]

My Chiron does this when the brushes go bad or are dirty but usually the amplifier will kick out as it pumps too much current trying to accel the spindle in the given time.
I know the brushes are going bad when my idle (non-cutting) power starts to climb.

I mucked up the brush holder alignment once and it did the same thing but you have to take the motor apart to mess this up.

Bob

 

[Bruce Griffing]

I suspect old electolytic caps in the drive (VFD I assume) OR one very weak or dead phase in the drive. Two key tests - both have been suggested. First check the current in each of the three legs that drive the motor (not the supply - the legs coming from the VFD to the motor). Check the DC bus voltage in the VFD - with the motor powered up but still (0 rpm) and again with it at full tillt (loaded). These tests will tell whether or not the VFD is working properly.

 

[Solar71]

One time our matsuura was acting a little strange.
It would run ok for about 15 minutes then trip.
We would reset it and it would be fine for a while then trip again.

Eventually we found out that it was one of the Fuses in the breaker.
It was not broken, but it was almost broken, so the power was not comming through
correctly. It was strange. You could check it with a meter and it seemed ok, but once in a while it would trip the machine. We changed it out and it was fine after that...

So it could be any little thing.

good luck

 

[scudzuki]

And a breaker is an easy inexpensive thing to change out.
Worst case you end up with a good spare breaker.

Joe

 

[adama]

All measurements for voltage drop need to be done as close to the drive input terminals as possible. Phase to phase voltage and phase to phase current. (phase to neutral voltage too can some times show a abnormality in some weird faults.) If that checks out good, then its time to look at the drive output - DC bus voltage.

If your experiencing minimal dropping of voltage under load that's about the best sign going that the wiring to the drive is fine. making sense of drive output power - current realy needs a better than normal multi meter and idealy a osilascope to look at whats realy going on in near real time. If you can actualy mesure spindle speed under load all the better.