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  1. #1
    This is driving me insane, I'm having problems with my CNC router I have two stepper motors driving the X axis and after cutting five or six things one of the stepper motors miss a step or two and of course it breaks the end mill then it will work again for another five and six parts, then it does the same. Now I have rewired the router with CY cable including all the wires in the control box. I have all the shield wiring in the control box connected to an earth at both ends and I have the limit switch's shield earthed at the control box only and I have the stepper motors shield connected at both control box and stepper motor I have also tried for the stepper motors just connecting the shield at the control box only, and its always the same.the two stepper motors on the X axis go out of sink one will run the other will stop for a few steps.
    At times when it is goes wrong as the whole machine stops for less than a second like someone froze the g code.
    I need help again.

  2. #2
    To be honest I had a feeling you'd be back when it was recommended you ground shields at both ends.!! Even thou changing this doesn't help it's still not something I'd suggest you do other than maybe on the VFD.

    Now back to your problem can you give more details of your setup.
    What you using to control it with Parallel port or some other motion control.
    What Control software and If Mach3 what Kernal speed.
    What's MicroStep on drives and Motor tuning settings for each axis.
    What PSU voltage
    What Make of BOB.

    Things to check now.
    Check couplers to motors are tight. Put a mark on shaft/coupler so you can see if they move.
    Check Accel and Steps per is set same for both axis.

    If this is losing or gaining steps consistantly at same time or distance then it won't be noise causing the problem, it will be either something loose or setup wrong.

    If using parallel port then Try a differant Parallel port cable is you have one. This is first thing I would try as matter of course.

  3. #3
    It's good that you were able to try the screens connected at both ends then one end only and the fault was still there.

    Are there any other programs running in the background on your PC ?
    Are you using X and A selected as a slave ?
    It might be a good idea to swap the driver boards around to see if the fault moves to the Y axis for example.
    Last edited by EddyCurrent; 25-03-2014 at 09:22 PM.
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

  4. #4
    I appreciate your help.
    I have the shield cable connected at both ends should I also disconnect one side inside the control box from power supply to the drivers . Just have the shield connected at the PSU end?
    Also I have the shield connected at both ends from the driver to the breakout board should I also remove the shield connection at the breakout board and just have the connection at the drivers side?

    What you using to controlit with Parallel port or some other motion control. I use a Parallel port.

    What Control software andIf Mach3 what Kernal speed. The software is Mach3 and the Kernal speed is set at 25000Hz

    What's MicroStep on drivesand Motor tuning settings for each axis. X axis Steps are 400.066 Velocity 1900.2
    A axis Steps are 400.066 Velocity 1900.2

    What PSU voltage PSU 400W 36 Volt / 11amp

    What Make of BOB. Breakout board HG07

    Stepper Motors 3.1 Nm

    I will get another Parallel port cable to try as well.

    The couplers to motorsare tight. And I also fitted a marker to see when It moves as I'm watching it all the time now but I can never be quick enough to stop breaking a end mill.

    I hope you can see something wrong.

  5. #5
    Are there any other programs running in the background on your PC ? No other programs running I only use this one to run Mach3 using windows XP.
    Are you using X and A selected as a slave ? Yes I have slaved the X and A axis.

    I could try swapping the drivers round to see if its sill faulty thing is it's not all the time it will be fine for 5 or 6 times that I use it then it misses a step or more last time it stopped the A axis and it turned the X axis stepper motor quarter a revolution when I hit the stop its going to do some bad damage if I don't get this sorted.

  6. #6
    Can't see any obvious troubles from the settings. Need to know the Accel settings as that could cause this more than anything else.

    The other thing that could cause this is how you have connected the phases of steppers to the drives.? The steppers have A+ A- B+ B- and the drives have matching A+ A- B+ B-. If you have wired them opposite way they will still work but it can cause you a Step to drop on every direction change if the pulse edge is on wrong side to drives. So it's important you wire them right way round.

    This can easily be seen by marking each motor shaft or there start position then running some short directional changing G-code moves and see if marks return to same spot when finished. Chances are one won't but other will if you have one wired opposite to other.

    Regards the sheilding then connect them just at the control box end on all of them. You only really need sheilded wiring on the Signal cables.

  7. #7
    I have just checked the wiring from the drivers to the stepper motors and it all looks good.
    A+ Red & Blue wires
    A- Yellow & Black wires
    B+ White & Brown wires
    B- Orange and Green wires
    I also remarked each stepper motor and both land in the same spot, I then ran a short G-code and that landed in the same spot, of course it will not when it misses a step.
    Now I have my setup in metric and I rechecked the motor tuning, I had the Acceleration set to 320. I got that setting from some where online but can not find it now, however I'm now thinking that this is to high should I start at 25 and work up till it breaks again then reduce the setting by 10% or is this wishful thinking.

  8. #8
    No if using Metric then 320 is quite low but don't go higher yet untill problem is found.

    Is it always the same Axis that goes wrong.?
    When you say it's missing steps then stalling motors are you sure this is happening or just presuming because motors stall.? Can you stop it after a while of cutting and see any positinal error.?

    Has it just started doing this since you re-wired or was it doing any of this before.?

  9. #9
    If it's the same motor every time is the ball nut okay, I say this because one of mine was jamming now and again due to too many ball bearings in it.
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

  10. #10
    Yes it's always the same axis that goes wrong X and A axis slaved. One stepper motor stops and the other keeps on going. I did a small line picture the other day and it started fine then half way through the cut it moved the rear part of the picture 12mm away from the front part. It will run fine and I even rerun a g-code today 11 times over the same picture and it will follow the same line spot on, then for no reason on the 12th time it will go and cut a line short and mess it up.
    The first time I really noticed it was when I first fitted a spindle and VFD in place of the router, Also when I first switched on the machine and seen it move for the first time, it did crash in to the limit switch for no reason I was jogging the x axis then it didn't stop but it's been OK till the spindle was fitted, Having said that I have seen it go funny with out the spindle running, on just a test run no end mill fitted.
    If I lower the acceleration down to 200 will this cause a problem if I try it at this setting for a few days.
    I have got to try something.
    When it goes wrong the g-code stops in it's tracks along with the machine and then carries on but not in the right place or one of the X or A stepper motors takes a extra second before moving with the other one.
    Last edited by Bush Flyer; 26-03-2014 at 01:22 PM.

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