Y axis jerking

Man Im gonna tell you, when it rains it pours with our Fadals. My current problem is the Y axis is jerking. It completed a part just fine. I went to jog the machine and the Y axis was jerking bad. It acted as if no lube was present on the ways. So i pulled the covers and it is indeed oiling. When I change the jog speeds, it becomes more pronounced. If the jog speed is slow, the jerk is low and pronounced. When you speed it up, the jerks occurs more rapidly. You can feel it on the table. So what do you think, drive card or servo. Keep in mind that this is a Numatix retrofit. The control has been running awesome, so I dont see that as an issue.
Thanks

Edit: I tweaked on the comp pot a little bit until it shook like crazy. I then hit the e-stop to stop the shuttering. I then adjusted the comp pot to the oriinal setting and it is now as smooth as ever. Go figure. If anyone has any ideas as to the cause, please post.
Thanks

The issue has returned. It did the same thing on start up this morning. I can jog it around to get it to go away but it comes back. Anyone have any input?
Thanks

iess525 helped with the issue I was having. He got me back up and running in no time at all. I would recommend him to anyone.
Thanks again!

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Originally Posted by 5th-axis

iess525 helped with the issue I was having. He got me back up and running in no time at all. I would recommend him to anyone.
Thanks again!

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No problem. Glad to help!

Ok so I swapped drives on the Y axis and it still "stuttered" when jogged. That narrowed it down to the servo. I have removed it from the machine and by looking at it on the bench everything looks ok. It spins freely as well. Could the tach cause this?

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Originally Posted by 5th-axis

Ok so I swapped drives on the Y axis and it still "stuttered" when jogged. That narrowed it down to the servo. I have removed it from the machine and by looking at it on the bench everything looks ok. It spins freely as well. Could the tach cause this?

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Yes the tach can be causing the problem. Are you using the standard glentek motors?

Had a tach go out a while ago. Huge shuttering problem. If you took the MPG and shook it back and forth a little, the machine would try to shake itself across the room.

Easy check, If I remember right, the tach should put out 7volts per 1000rpms.

You've got the motor on the bench, easy to check. The small black and red wires, thats your tach. Get a cheapie 500rpm drill, hook it up to the motor and spin her, you should get about 3.5volts. I would hazard a guess that if you are above 3, you are good, I had one motor (taken out for comparative purposes) that was working fine putting out about 2.9V per 500rpms.

Word to the wise, you CANNOT rebuild the little magnet pack, DO NOT take it out, it will fall apart and then you have to buy the whole damn thing, or like me, take one out of a working motor to replace the bad one, and end up buying 2. Check the brushes first, cheap to replace. My problem ended up not being with the magnets, it was the (think with wound wires) had a few dead spots in it. Easy to check with a continuity tester.

Eagle machine had tachs in stock for I think $170.

Why that makes it shudder, the control has no idea how fast the motor is going and if its putting out low voltage or has dead spots it will send more voltage to the motor to speed it up and it overshoots, then comes flying back.

I removed the servo and cleaned the brushes on the motor and tach. They were extremely dirty. All is good now.
I know what you mean about the magnets on the tach. When we cleaned the X-axis motor last week, one segment fell out. I just super glued it back in place. It is currently running ok. Was it not a good idea to glue it back in?
Thanks for the reply

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Originally Posted by 5th-axis

Was it not a good idea to glue it back in?
Thanks for the reply

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Hey if it works....

Here is a thread from when I was trying to figure this out.

http://www.practicalmachinist.com/vb...roblem-181334/

Very informative post little bubba. Thanks again. The original problem with the X-axis was that it would run away and the Amplifier would show a high speed ecb fault. We removed the servo and replaced the bearings and cleaned it up real well while waiting for the replacement amp. Thats when we found the broken magnet. The machine runs OK but i feel that something is not quite right with it. When we assembled everything we had to swap motor leads to get it to run. I just figured we got something out of phase but its running. Now when I jog the machine it seems to take a little time to get up to speed. By a little time i mean miniscule, just enough to see with the eye. You can also hear it. By what you have told me and the post you directed me to, I may indeed need to replace the tach on the X-axis. Do you have an opinion on this? Im not a complete noob at this. At my last job I was a maint. tech. at a major tapered roller bearing manufacturer but my emphasis was on mechanical systems and not electrical, although I did pick up a few things on the electrical side. Sorry for the wall of text but your help is greatly appreciated.

IF YOUR STILL HAVING A D.C. SERVO PROBLEM, EXSPECIALY AFTER YOU HAVE CLEANED THE TACH BRUSHES TAKE A CLOSE LOOK AT THE TINY SPRING TENSIONERS - I HAVE FOUND THAT IF AT LOW FEED RATE (g1 f20.) NOT USING YOUR M.P.G. FOR JOGGING YOU CAN FEEL AT A REGULAR INTERVAL WHAT FEELS LIKE A THUMP - EITHER THE BRUSHES ARE WORN TO POINT WHERE THEY ARE NOT MAKING GOOD CONTACT AND/OR IF YOU USED A SOLVENT TO CLEAN OUT THE CARBON BRUSH DUST IT CAN ACTUALLY CAUSE THE BRUSHES "STICK" IN THIER SLOTS - ALSO YOU NEED TO USE A OHM METER TO VERIFY THAT THERE IS NO CONTINUITY IT THE SERVO'S GROUND - NO CONTIUITY IS ACCEPTABLE - SERVO REBUILDER USE A METHOD OF "BAKING" ALL IT IS IF YOU HAVE CLEANED A SERVO'S ARMATURE INCLUDING IT'S TACH - I HAVE HAD SUCESS USING AN OLD TOASTER OVEN AND "BAKING" THE WHOLE AMATURE AT NO MORE THAN 120 DEGREES FOR MINUIM 2 HOURS - IT' NOT MAGIC IT JUST EVAPORATES ANY MOISTURE THAT THE CARBON DUST CAN USE AS A PATH - GOOD LUCK

OK so after cleaning the motor and tach brushes up the machine ran fine for 1 week. It started the stuttering again today every so often. Sometimes it would be in the positive direction, sometimes in the negative direction, sometimes both directions or not at all. Im seriously considering replacing the whole servo. I may try 1 more cleaning and a closer inspection of the tach and brushes. Anyone know of a good source for brushes?

Not sure if this post is redundant, as I can't tell for sure if you've done this. The brushes (both motor and tach) ride on a segmented disc called a commutator, which is copper. The O.D. of the comm gets dirty from the carbon brushes running on it, and can get contaminated with coolant, oil, etc. When you have one bad spot on the tach comm that doesn't conduct electricity to the brush face very well, it results in the thumping, cogging, swelling, whatever word you want to use to describe a not-smooth rotation. You have to clean the O.D. so it is bright copper. Being copper, it's fairly soft, so you don't want to scratch it excessively, leaving a rough finish that wears the brushes faster. If it's oily or wet, clean it with contact cleaner first. I use a fine Cratex stick to polish it. I've heard of others using a pencil eraser, but I have found them not abrasive enough to clean, and too soft so they leave their little rolls of junk behind.

This should be a regular maintenance item for a DC motor equipped with a tach. The motor drive works extra hard when a swelling tach signal if fed back, as the drive tries to smooth out what it perceives as a jerking motor speed. In reality, the drive causes the jerking by not putting out a steady voltage to the motor.