[ibuildstuff4u]

I have a D&M milling machine that I converted to run with Mach 3 software and have a strange problem with the Z axis. Once and a while the Z axis motor acts up and only runs in one direction no matter what I tell it to do. If I play around with the software settings I can get it to go the other direction for a moment and then it resumes it's problems and only runs in one direction. I had this problem in the past and it went away by it's self after messing around with the machine for a while. The problem came back this week after I unmounted the stepper motor to adjust the ball screw and put it back on, none of the wiring was unplugged when I did this. I also tried a different stepper drive in the past and the problem didn't go away so I don't think the drives are at fault.

Could there be a short in the motor wiring or can the direction signal get messed up by interference inside the machine? I have looked at every thing and it seems OK, and hope someone can tell me where I should start trouble shooting for the problem.

Thanks for the help!

Dale P.

[SCzEngrgGroup]

There's no way any motor fault could possibly cause that behavior. Since you've presumably ruled out a fault in the stepper driver by swapping it out, the most likely cause is a marginal driver on the parallel port, breakout board, etc. which causes the direction signal to not always be asserted strongly enough, or a loose/intermittent connection in the wiring, cracked PCB trace, etc. But your problem almost certainly lies somewhere in the path of the DIR control signal.

Regards,
Ray L.

[ibuildstuff4u]

Ray, that's what I'm thinking, but this is the third time this has happened after messing around with the Z axis motor. It's really got me confused on why it's happening. I guess I will have to open up the machine again and try swapping drives and inputs around and see if I can find where the problem is.

Thanks for the help!

Dale P.

[SCzEngrgGroup]

Swap the wiring between the X/Y axis motors. I can guarantee you'll find the problem follows the electronics, not the motor. Next put the motor wiring back, and swap the Step/Dir lines between the axes. This time, I'd bet the problem moves to the other axis, which tells you the problem is *at or before* the Step/Dir signals. What BOB are you using? What stepper drivers? What is your PP voltage? How is everything powered/grounded?

Regards,
Ray L.

[Fixittt]

any time I have seen behavior like this, it has been because the cable going from the computer to the BOB is not seated all the way. Tripple check the cable connections and the BOB wires. Something maybe loose. If all your connections are solid try removing the BOB from any backplate holding method and plug the cable straight to it and recheck.

[Numb Nut]

I'd be tempted to try to measure the voltage level on the dir input, right at the drive while trying to wiggle the connectors, cables, etc and check that the voltage isn't interrupted. An analogue multimeter is better for this kind of troubleshooting since the needle will show short voltage glitches that a digital meter can't respond to.

If you see no glitches then it might be the drive so try swapping it out with one of the others (you said you have already tried this, so seems unlikely).

[Torchhead]

That is a Campbell Designs BOB and there should be LED indicators to show you Step & Dir status on the pins. If the signals change there but not at the mootrs then the problem is AFTER the BOB. If it dies before there then you need took at your connections and the PC.

TOM Caudle
www.CandCNC.com

[ibuildstuff4u]

Thanks for all the help guys!

Yes the breakout board is a Campbell Designs board and the stepper drives are the original ones that came in the machine from D&M. I have two extra ones and added one of them to the machine for a fourth axis so swapping drives around is as easy as switching a few wires. I know I did that in the past when I had this problem, but I don't remember the outcome. I just remember that the problem went away after messing with it for a while which makes me think there is a short or bad wire some where.

The step and direction lights light up just fine so the problem must be between the breakout board and the stepper drive. I opened up the back of the machine last night and the problem went away as soon as the back door was opened. I checked all of the connections and didn't see any problems so I buttoned it up and ran the machine for a while. At one point the drive acted up again and a simple wack on the side of the case made it go away so I must have a bad wire or something inside the machine. I guess my next move will be to swap out the drive unit and possibly change out the wires that connect it to the breakout board. The wire harnesses for the stepper drives were recycled from the old system so there could be a fault with one of them.

Thanks again for all the help! I wasn't sure if a short in the motor wire could cause this problem and I was going to start there because I was messing around with the Z axis motor when the trouble started. Your answers saved me the time and trouble of rewiring the stepper motor and pointed me to the real source of the problem.

Dale P.



This is the inside before the retrofit, and after.

[SCzEngrgGroup]

I would check the BOB for a bad solder joint as well. And, if it has those removeable terminal blocks for all the wiring connections, remove them, and re-seat them a few times. Could just be some minor corrosion.

Regards,
Ray L.