Current through mill spindle. WTF?

Black Dragon wrote:


If the spindle is directly driven by the motor with no belts, you have leakage in the motor winding. A check with a good megger will quickly prove that out.
Perhaps, too, that the ceramic bearings themselves are generating the voltage. ( Piezo electric principle).
John
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john wrote:

If that's the case, how can it be resolved?
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Black Dragon

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I seriously doubt that it is piezio electric in nature. Piezo electric materials are typically crystalline materials and ceramic bearings are I believe amorphous materials.
Gary H. Lucas
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Gary H. Lucas wrote:

Ceramic exhibits piezo electric properties.
http://www.americanpiezo.com/piezo_theory/behavior.html http://www.americanpiezo.com/piezo_theory/ceramics.html
After looking at these sites, it seems that even though the hard ceramics used in bearings are not very good at generating electrisity, they still do generate a little.
John
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Black Dragon wrote:

Couple it to a transformer and sell it back to your public utility :)
If the bearings themselves are generating the voltage I would not worry about it. You could put a wiper somewhere on the spinde connected to the machine base but A couple of volts between the spindle and the machine would only hurt the bearings if they were metalic.
You might call the bearing company and check to see if this is a condition of using ceramic bearings. A conductive grease on the bearings might stop it but I would not do that unless the bearing mfgr. recommended it.
Piezo electric flow happens in the barbeque igniters,microphones, transducers and a lot of other equipment and sensors. I would highly suspect this is the cause of your problem. I wonder how it would sound if you ran it through an amplifier to a set of speakers, one for each machine? :)
John
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Black Dragon wrote:

Possibly arrange a brush contact on your spindle wired to some part of the machine that is at earth pontential.
I guess if you are brave enough you could determine if this is the case by using a wire grounded at one end and touch the other end on the spindle while you are seeing this.
Wayne...
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Wayne Weedon wrote:

Wayne:
    Much better than touching the toolholder, or creeping up on a piece of stock with the toolholder.     I still think you'd create more excitement if you had the boss put one hand on the table and then touch the toolholder with the other one. LOL
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BottleBob wrote:

Or his tongue...
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John R. Carroll
Machining Solution Software, Inc.
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That's weird--BUT...(and as as someone else has already suggested)...concievably this could only could happen if there's ceramic bearings.
I say it's probably really nothing to worry your head about.
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SVL







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up"
Thing to do, (I spose) is to see if you get any kinda "jolt" after the spindle has stopped, when releasing the tool manually--IF so, suggest then always run the atc in order to cycle in a different tool beforehand.....
Then next time the bearings get replaced, specify or even mix for yourself some small amount of graphite or other conductive substance into the grease.
Fwiw, one of our cats simply loves it--vigorously pet his fur...then touch his nose....
Bzzzzttt !!!
--
SVL





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PrecisionMachinisT wrote:

Where there's a spark there's likely to be erosion if I'm not mistaken, correct? Where's the current going? Is it finding its way down through the ball nuts, into the screws, and out the servos to who knows where, and it there enough to do any damage to those components in the long run?
Those are some of the things that started going through my head when I first saw the sparks.
I do believe there's justified reason for some concern here.
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Black Dragon

The penis mightier than the sword.
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Black Dragon wrote:

Convert it into an EDM machine :)
Unless you can determine where the voltage is coming from you cannot determine if it will damage anything.
You did say that you had another older machine that has been running for quite a while that was producing sparks too. If that machine is still running fine, I would not be too concerned about it, only interested as to why it is making sparks.
John
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On Sat, 12 Aug 2006 09:38:20 -0400 (EDT), Black Dragon

<snip> ======================I note that you are a new hire. I will pass on a bit of advise that my Father passed on to me, and which I ignored for some time to my cost. "No body likes a wise-ass."
Having got that out of the way, see below:
googled on >bearing failure "induced current"< and got c. 17,000 hits
see http://www.eeco-net.com/eec/uploads/Southwire%20VFD%20Wire.doc http://www.reliance.com/pdf/white_papers/Inverter_Driven_Indct_Mtrs_Shft_Brngs.pdf (I had to view html version at http://64.233.161.104/search?q che:AzfIA4ZZ3vYJ:www.reliance.com/pdf/white_papers/Inverter_Driven_Indct_Mtrs_Shft_Brngs.pdf+bearing+failure+%22induced+current%22&hl=en&gl=us&ct=clnk&cd=3) http://www.gaussbusters.com/ppm93.html
let us know what you find & what happens -- inquiring minds want to know.....
Unka George (George McDuffee)
...and at the end of the fight is a tombstone white with the name of the late deceased, and the epitaph drear: A Fool lies here, who tried to hustle the East.
Rudyard Kipling The Naulahka, ch. 5, heading (1892).
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F George McDuffee wrote:

I've been hired to help get their cnc machining under control. They *want* me to find problems and address them. Fixing machines is going to be easy. Fixing personnel and methods issues is not.
Thanks for the links.
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Black Dragon

"Go to Heaven for the climate, Hell for the company."
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On Sun, 13 Aug 2006 13:47:16 -0400 (EDT), Black Dragon
<snip>

<snip>
You are 90% of the way to being a big success as a consultant. Drucker and Cosby move over ....
Keep telling yourself -- "I will not attempt to solve non-technical problems with technology -- I will not attempt to solve non-technical problems with technology -- ..."
It can be exceedingly helpful to have a good working relationship with a qualified/experenced Industrial Sociologist or Group Dynamics practitioner when you encounter situations where the problems are mainly organizational/relational rather than technical. If you are close to a University, talk to the sociology and/or psychology departments. You can also find good people in the Human Resource Development programs, not so much so in the Human Resources Management programs (these tend to be a more business/finance oriented).
While not a priority item, it would most likely be worth your while (if you have not done so) to take an Abnormal Psych and Industrial Sociology classes [If you audit the classes you generally don't have to go through the enrollment/marticulation drill] so you can recognize the situation before getting "sucked in" a "no win" assignment. If possible you want the graduate seminar classes as these have the people "what been there and done that" and they are trying to figure out how they got so many knots on their head....
A place to start is Ken Kiser at Oklahoma State University. He teaches, but also does considerable consulting work. He was on my dissertation committee and is very knowledgable about the way all sizes of organizations operate. Tell him George McDuffee sent you. Email: snipped-for-privacy@okstate.edu http://sociology.okstate.edu/faculty/KenKiser.html KEN KISER. PROF:, KEN KISER. Address:, 025 CLASSROOM BUILDING. STILLWATER, OK 74078 -4062. Phone:, 405-744-6112. Fax:, 405-744-5780 ...
I only wish that I had taken the course *BEFORE* I started consulting.....
Unka George (George McDuffee)
...and at the end of the fight is a tombstone white with the name of the late deceased, and the epitaph drear: A Fool lies here, who tried to hustle the East.
Rudyard Kipling The Naulahka, ch. 5, heading (1892).
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On Sat, 12 Aug 2006 09:38:20 -0400 (EDT), Black Dragon

Maybe you could try calling the tech support of the company that built the machine. Shoudn't cost anything.
Rocky
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Rocky wrote:

Had a similar situation with large laser. Everytime gantry came close to job support, small spark!
Checked all wiring within machine, then moved (with forklift) machine away from wall - found +- 15meters of mains cable coiled up in neat, tight coil behind machine. Replaced with short mains lead - bye-bye spark . .. .
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Rocky wrote:

The machine is a month or two old and under warranty. Allegedly all the Miltronics techs are busy at some shop that has about 40 of their machines and got flooded with four feet or so of water.
A factory tech is going to be in some time this week to address a squareness problem, and the entire purpose of my original post was so I could have a bit of understanding about what could possibly cause electrical current to flow through a machine spindle. I fully admit to being clue impaired when it comes to electricity.
I don't have time to reply to all the most excellent posts on the subject, but thanks much guys.
George... me a consultant? Meheh. I definitely would make a better insultant, don't you think? <g>
FWIW, I measured the voltage of the rotating spindle again while it was cutting. When the tool was engaged in the cut the voltage fluctuated between .5 and 1.5 volts, and when the tool exited the cut on a entry / exit arc move it jumped up to around 10 volts, then back down to .5 / 1.5 when back in the material.
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Black Dragon

Religion is fine, Churchianity sucks.
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Oh, I see their in NO last yr <G>.
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Probly wouldn't be very difficult or expensive to retro a brush to shunt current from the spindle to it's housing after the fact.
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