denford micromill y axis issue

[creighta]

I have been working on a Denford EMC2 conversion. I have a denmint board wired to my pc parallel port. When I jog the machine in EMC2 everything seems great, but the Y axis gets confused on what direction it should be going. Sometimes it runs correct then stalls. When this happens if I stop jogging then start again it decides to run in the opposite direction. Sometimes it just jitters back and forth instead of running at all.

I have removed the motor from the table and it still does the same thing with no load. Any ideas what I should be checking?

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[hndswthtshdws]

Swap the motor and use a different known working motor on the y axis. If the problem persists then this rules out the motor.

If not the motor -> Go into EMC2 setup and see which pin controls direction on this motor. Probe that pin on the card with your multimeter. It should read +5v when you tell the motor to spin one way and 0v when you tell the motor to spin the other way.

If motor changes direction without changing signal -> check card for loose connections, its not a computer or motor problem.

If signal changes when its not supposed to -> try a new parallel cord, sometimes they have a bad connection. If not the parallel cord its the computer.

[DICKEYBIRD]

I have a MicroMill as well but run it on Mach3; works great. It has the SmartStep/3 controller with the top card removed.

You can download and use Mach for free temporarily to determine if it's an EMC setup issue.

Mach's real easy to set up. EMC may be easy for you though...wish I could say that 'cuz I'd love to use it on my lathe!

[creighta]

I had an old PC available and already had a Linux emc disk so I went that route. I checked and am only getting 3.2v on the pin, but if I swap the x and y pins the y still does not work, but the x does.

I took the motor apart and it looks new, but there is one small pinhead spot on the armature that has the magnets exposed. I put clear nail polish on that and he motor was fine for a few cycles. Still undecided if this is a software issue or motor. The stepconf runs, but has direction issues but the emc jog just jitters.

[SCzEngrgGroup]

I took the motor apart and it looks new, but there is one small pinhead spot on the armature that has the magnets exposed. I put clear nail polish on that and he motor was fine for a few cycles. Still undecided if this is a software issue or motor. The stepconf runs, but has direction issues but the emc jog just jitters.

If you have disassembled a stepper motor, then you've pretty much ruined it. Simply disassembling a stepper will reduce its torque capability by 30% or more.

Regards,
Ray L.

[manton]

If you have disassembled a stepper motor, then you've pretty much ruined it. Simply disassembling a stepper will reduce its torque capability by 30% or more.

Regards,
Ray L.

I'm curious as to what this would be based on. These are pretty simple devices, and I would be hard pressed to believe that if they are carefully reassembled, that they wouldn't function the same as when the were assembled originally. Assuming that the bolts are torqued down in an appropriate pattern, so as not to cause twist in the housing.

[109jb]

I'm curious as to what this would be based on. These are pretty simple devices, and I would be hard pressed to believe that if they are carefully reassembled, that they wouldn't function the same as when the were assembled originally. Assuming that the bolts are torqued down in an appropriate pattern, so as not to cause twist in the housing.

Don't know the science behind it, but it is true. I remember a post by Mariss from Gecko where he did an experiment and disassembled one and put it back together. He ran torque tests before and after and the torque after reassembly was significantly lower. I don't remember the exact numbers but it was about like Ray said, 30% lower torque.

[SCzEngrgGroup]

I'm curious as to what this would be based on. These are pretty simple devices, and I would be hard pressed to believe that if they are carefully reassembled, that they wouldn't function the same as when the were assembled originally. Assuming that the bolts are torqued down in an appropriate pattern, so as not to cause twist in the housing.

Servo Motor Disassembly | Servo Motor Magnetization

[Al_The_Man]

I have never disassembled a stepper, but have overhauled servo's in many cases.
The theory is that a 'Keeper' should be used, either around a rotor, or in a stator to retain the magnetic field, otherwise the P.M. magnetic field can diminish.
So far with servo's I have never had a problem in not using a 'Keeper', many motor manufacturers will state there is no detriment to removing the rotor, due to the quality of the rare earth magnets used.
As an aside, I have many stator magnets removed from servo motor that were unrepairable, using them for various functions around the shop, after many years, I cannot detect any weakening of these very strong magnets.
Al.

[creighta]

Motors are simple devices, and this one is most likely bad anyway. Before the disassembly I could touch the shaft and cause it to stall and jitter. Afterward i had to actually hold the shaft between my fingers to cause any detectable loading. This didn't last long though.

The small bare spot was only about 8 thousandths diameter and everything else looks new, but I am guessing the years of setting unused and covered in acrylic shavings caused a momentary short that created my problem. Plccenter has one for $152 or can rebuild this one for $68

[DICKEYBIRD]

Plccenter has one for $152 or can rebuild this one for $68

Whoa, step away from the credit card! You can almost get 3 modern motors for that kinda dough. PLC is high as a cat's back on most stuff.

Did you ever switch motors around to verify what's wrong? You can do it at the controller itself. I suspect you got a bad chip in the driver circuit for that axis. Trace the wires down for that motor and switch them over to another axis' connections. If the problem persists then you have a bad motor (doubtful) or shorted wiring between the controller and the motor.

I had a similar problem recently on my lathe retro and I just knew my controller was bad. I finally traced it down to to a short between 2 wires on a splice in the stepper cable I'd done a week or so before. Sharp corner of soldered wire poked clean through 2 layers of heat shrink. Until that day, I just knew all of my splices were perfect. Yeah, RIGHT! Ate humble pie that day!

If it is bad chip(s), you can get them cheap and replace them yourself. (Or at least I've read about others doing it over on the Denford forum.) Search for something to do with "L297 and L298" chips and Denford.

[SCzEngrgGroup]

Motors are simple devices, and this one is most likely bad anyway. Before the disassembly I could touch the shaft and cause it to stall and jitter. Afterward i had to actually hold the shaft between my fingers to cause any detectable loading. This didn't last long though.

The small bare spot was only about 8 thousandths diameter and everything else looks new, but I am guessing the years of setting unused and covered in acrylic shavings caused a momentary short that created my problem. Plccenter has one for $152 or can rebuild this one for $68

First, stepper motors are not as simple as you seem to think. If you understood them, you would know this. Disassembling them WILL damage them, and a few minutes with Google will prove that. Second, sitting idle, and being covered in acrylic shavings will have NO effect whatsoever on a stepper motor. Acrylic is NOT conductive, and CANNOT cause a short, momentary or otherwise, and CANNOT even damage the insulation on the windings. You seem to be finding explanations that make you feel better, but they are flat out wrong and not technically plausible.

Regards,
Ray L.

[hndswthtshdws]

It could be that your card is designed to work with a 5v parallel card and your 3.3v parallel card is enough to make some of it work.

[creighta]

Swapped axis motors and the good motor would not run on the y axis either. The "bad" motor works great on another axis, so am looking for l297 motor controllers now. Picked up some sockets for them, but RadioShack doesn't keep 297 s in stock.

[DICKEYBIRD]

Cool, now you're getting somewhere. Did you look at the board closely & see if there's obvious evidence of fried chips?

Hopefully you found some info on replacing the chips? Keep us posted.

[wizard]

I'm curious as to what this would be based on. These are pretty simple devices, and I would be hard pressed to believe that if they are carefully reassembled, that they wouldn't function the same as when the were assembled originally. Assuming that the bolts are torqued down in an appropriate pattern, so as not to cause twist in the housing.

Pulling the armature out of a stepper will ruin it. At least most that I know about. The armature needs to be in place to prevent demagnetization.

[creighta]

I have not pulled the board yet. I will when I get the chips, but I do not see any burns. I teach high school engineering and electronics, so I have a pretty good handle on the chip swap and I also have an IC tester to check the 297 when I pull them.

I don't want to argue, but the stepper is fine now that it has been reassembled. I wouldn't take it apart and leave it for months, but pulling it apart, cleaning it, and putting it back correctly will not ruin it. IDK about less torque, but it still runs great and has just as much power as the others that I didn't work on.

BTW thanks for all of the help, I would not have figured this out w/o all the replies.

[DICKEYBIRD]

I teach high school engineering and electronics, so I have a pretty good handle on the chip swap and I also have an IC tester to check the 297 when I pull them.

Make sure to post some pics and document the process so you can teach me as well! Many electrons have died an agonizing death when I'm around them.

[creighta]

We finally got the 297 sockets in and the new ICs but the problem persisted. We also changed out the L298 controller and still the same issue. I am starting to run out of parts to inspect here. Only have about $15 in repairs so far it may be time to start looking at Hobby CNC or Gecko boards.

Anyone try using 4n25 optocouplers to overcome low voltage from a parallel port?

BTW, I tried posting pics but can't w/o using photobucket which is blocked here.

[DICKEYBIRD]

Well dangit, I was wishing good results for you!

You should be able to attach your pictures to posts by the "Manage Attachments" button in the "Additional Options" box.

Got another old PC to try instead of a laptop?