Causes for a False Spindle Load reading?

Kevin Wilkins · Apr 18, 2013

I just bought a 2001 Mini Mill used and am in the process of getting it running. The main spindle load reads anywhere from 25-50% when it is just turning without doing any cutting. The load is the same on the analog dial and on the screen readout so it doesn't seem to be a bad guage.

The local Haas Guy has been testing things:

1. The main motor spindle turns easily by hand, so it's not really binding. There does seem to be a slight noise from the motor bearings but not too bad.

2. The encoder is OK, we swapped for a known good one and the load was still indiated.

3. The signal is coming from the 45 amp vector drive card in cabinet.

He thinks it is the vectr drive but could be something in the main motor.

Does anybody have any ideas or tips?

Thanks in advance!

Kevin Wilkins · Apr 25, 2013

Nobody has any ideas?

BGL · Apr 25, 2013

- Check output voltage from transformer per manual.
- Check amperage draw at motor lead with clamp on meter.
- Check amperage at pin outs on control card

fpworks · Apr 25, 2013

Is it a belt drive?

Does the load increase with rpm? Is the load stable at any given rpm?

Kevin Wilkins · Apr 26, 2013

Thanks for the tips!

It is abelt drive and the load reading stays the same regardless of RPM.

taity · Apr 26, 2013

Get to the spindle motor, remove the connection cover, if it smells burned, get it rewound. High amps can be a symptom of a worn induction motor, meter readings don't always detect.

Kevin Wilkins · Apr 27, 2013

Thanks, the cover is already off, I'll give it the sniff test monday. I sure hope it is a wonky vector card and not that big motor!

DMF_TomB · Apr 27, 2013

spindle load readings

Kevin Wilkins said:
I just bought a 2001 Mini Mill used and am in the process of getting it running. The main spindle load reads anywhere from 25-50% when it is just turning without doing any cutting. The load is the same on the analog dial and on the screen readout so it doesn't seem to be a bad guage.
The local Haas Guy has been testing things:
1. The main motor spindle turns easily by hand, so it's not really binding. There does seem to be a slight noise from the motor bearings but not too bad.

2. The encoder is OK, we swapped for a known good one and the load was still indiated.

3. The signal is coming from the 45 amp vector drive card in cabinet.
Thanks in advance!

.
who says it is a false reading? all drives use power even when not cutting. If you have a gear box that can easily absorb power. the motor can absorb power just turning. i was always taught a average motor needs 4x it's rated current on startup so a meter that shows 25% load i would easily expect.
1) higher speeds absorb power
2) thicker lubricant (oil and grease absorbs power)
3) preloaded bearings for tighter spindles absorb power
4) bearing seals to keep dirt out absorb power

Kevin Wilkins · Apr 27, 2013

The Mini Mill does not have a gearbox. Normally, the spindle load meter should not read around 30% load when the spindle is just turning without even a tool. My TM1 reads zero just turning. The Haas Tech is coming round Monday morning to install the rebuilt spindle and I'll show him this thread. I hope I can get away without spending anymore cash on the machine untill I can make some cash with it!

DMF_TomB · Apr 27, 2013

amp meter

Kevin Wilkins said:
The Mini Mill does not have a gearbox. Normally, the spindle load meter should not read around 30% load when the spindle is just turning without even a tool. My TM1 reads zero just turning. The Haas Tech is coming round Monday morning to install the rebuilt spindle and I'll show him this thread. I hope I can get away without spending anymore cash on the machine untill I can make some cash with it!

.
i would use a clip on amp meter to read amperage it is using and compare to it's rated amp usage. i have never heard a load meter reading 0 if turning especially at higher speeds unless that particular machines load meter is not calibrated.
.
I have seen other makes of machines read 10-50% and not even cutting just turning a tool. it heavily depends of what rpm spindle is turning at.

Kevin Wilkins · Apr 28, 2013

Maybe here are some other Mini Mill owners out there who can check where their load meter is reading when just turning?

DMF_TomB · Apr 28, 2013

most machines have overload protection. that is with high current usage over 10 seconds they will trip the overload and shut down. i know of no properly installed machines without overload protection.
.
the load meter i use to determine if a cutter is dull. if normally cutting at under say 40% and after a lot of cutting it starts getting over 40% then it is probably getting dull. on my Mazak CNC mill i can set a variable feed control where if an overload is occurring after 5 seconds the feed will automatically start being reduced. i look at load meter but it is not like i trust it for everything. it is not unusually for machines to be rated at over 100% load for less than 20 minutes. the theory being as long as it get time at under 100% duty cycle to cool down short term use over 100% normally does not bother the motor.
.
the load meter is normally an amp meter and i have never heard of a motor running using no amps so normally a load meter would show something when a spindle is turning unless someone adjusted it to read zero when not cutting but motor is turning

Kevin Wilkins · Apr 28, 2013

My TM1 shows zero load on the spindle load meter when the spindle is not cutting simply turning. There are two spindle load meters on the machine, one is an analog needle guage and the other is a readout in operating system. Both are showing the same reading.

The Haas Tech here does not think it is normal that the Mini Mill is showing around 25-30% load when not cutting. The question is why it is showing a load when there isn't one. I'm hoping it is not in the winding of the big spindle motor because having that thing rewound will not be a cheap fix. He's coming round tomorrow to install the rebuilt spindle and we'll see what it reads then and I'll show him this thread.

annoying · Apr 28, 2013

I sure wouldn't be having him put in a rebuilt spindle just yet. If it spins easily and not too noisy, your might well be wasting money with a swap.

I'd expect the meter is on a current sense and there could easily be some bad components involved. Does it fluctuate as one would expect when ramping up speed? Why not do some cutting to see how it acts? If you have specs on the motor, you could try using a clamp meter and see what percentage you are at with that measurement.

Kevin Wilkins · Apr 28, 2013

The spindle was rebuilt to change the bearings from from air / oil mist to packed grease because I don't have a screw compressor and cannot operate the machine otherwise. That didn't have anything to do with the load reading.

I expect the Haas guy will do some more load tests on the motor tomorrow.

annoying · Apr 28, 2013

Kevin Wilkins said:
The spindle was rebuilt to change the bearings from from air / oil mist to packed grease because I don't have a screw compressor and cannot operate the machine otherwise. That didn't have anything to do with the load reading.

I expect the Haas guy will do some more load tests on the motor tomorrow.

Oh, Okay. Thought you were swapping to try to get a fix

annoying · Apr 28, 2013

Kevin Wilkins said:
The spindle was rebuilt to change the bearings from from air / oil mist to packed grease because I don't have a screw compressor and cannot operate the machine otherwise. That didn't have anything to do with the load reading.

I expect the Haas guy will do some more load tests on the motor tomorrow.

Oh, Okay. Thought you were swapping to try to get a fix

DMF_TomB · Apr 29, 2013

grease

Kevin Wilkins said:
The spindle was rebuilt to change the bearings from from air / oil mist to packed grease because I don't have a screw compressor and cannot operate the machine otherwise. That didn't have anything to do with the load reading.

I expect the Haas guy will do some more load tests on the motor tomorrow.

.
grease uses more power. if spindle turns easily then maybe grease at high speeds absorbing power especially if quantity of grease is high. most bearings are only suppose to have 1/4 - 2/3 fill in grease and more than that can cause usually minor problems

SIM · Apr 29, 2013

I had a high load reading on my Ol' VF-1. Turns out one of the wires to the Analog Gauge had a funky connection. Soon as that was taken care of, the load reading went down to where it should be.

I am not 100% sure if the digital gauge picked up the same readings...but I really think it did as I recall having to run small drills and light cutting EM's with real high Tool load readings not to alarm out.

First time around I just asked about the reading and service tech checked motor and said it was all okay and not to worry about it....but I worried and the next visit he was inside going thru it for me and we found it...I say "we" as he poked I saw needle drop. Really could have done myself...but early on and the machine was intimidating.

Another issue when tech installed new motor...a parameter was off and showed real high readings till he nailed down the right setting.

Let us know...hope its a quick fix.

DMF_TomB · Apr 30, 2013

sometimes wire connections get hot and need to be taken apart and redone.
.
we had a caustic tank with electric heaters and every few years the aluminum wire lug connections got so hot the electrical tape caught on fire. once the electrical wire connection was cleaned and redone the connection no longer got hot. welding cable connection do the same thing.
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also saw a overhead crane got wired to 440 volts and motor was 220 volts. it made a sound like compressed air as it arced and burned out. you would think electrician would check the voltage before wiring something but sometimes even if voltage checked maybe machine itself is wired or set for a different voltage.

Causes for a False Spindle Load reading?

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