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  1. #1
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    Sep 2009
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    26

    Possible Mach3 Bug

    This is a rotary job. When the following code section is run, the Z-axis hums and loses steps when
    executing the marked lines of code. However, the Z-axis should not be moving at all.

    N8420 G1 A-108.2132 Y0.8183 Z-0.2678
    N8430 G1 A-108.4755 Y0.8183 Z-0.2751
    N8440 G1 A-108.8690 Y0.8183 Z-0.2889
    N8450 G1 A-109.0002 Y0.8183 Z-0.2944
    N8460 G1 A-109.1314 Y0.8183 Z-0.3022
    N8470 G1 A-109.2625 Y0.8183 Z-0.3358
    N8480 G1 A-114.5094 Y0.8183 Z-0.3358 <---------------
    N8490 G1 A-114.5095 Y0.8183 Z-0.3358 <---------------
    N8500 G00 A-114.5095 Y0.8183 Z2.7500
    N8510 G00 A-114.5786 Y0.8246 Z2.7500
    N8520 G00 A-114.5786 Y0.8246 Z2.3000

    Removing one of the marked lines, everything is fine. Worked on it for two days, and cannot find the cause.

    Any suggestions would be greatly appreciated.

  2. #2
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    Nov 2012
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    1101

    Re: Possible Mach3 Bug

    I've had a cheap TB6560 board that would lose steps on one particular line of one particular G-code file. I guess it was some sort of a resonance issue. Try changing your feed rate slightly and see what happens.

  3. #3
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    Nov 2008
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    496

    Re: Possible Mach3 Bug

    Hums and loses steps usually happens if your acceleration or speed on the drive is set too high.


    Sent from my iPhone using Tapatalk

  4. #4
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    Re: Possible Mach3 Bug

    The drive can keep up with the acceleration/speed settings throughout the whole file (173,000 lines) except on that one line pair. And that line should not even be attempting to move the z-axis. Both lines are almost identical, yet, just removing one of them fixes the problem. It seems that if the y-axis and z-axis do not move, and the a-axis moves only a very small amount on the second line of the pair, that is when the z-axis tries to move and loses steps. It just does not make sense!!!

  5. #5
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    Nov 2008
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    Re: Possible Mach3 Bug

    That’s weird. Those two lines can’t be the problem. After that many lines are the steppers getting hot?


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  6. #6
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    Aug 2009
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    1055

    Re: Possible Mach3 Bug

    ...Wild guess, this may have something to do with the type of Feedrate mode switching used during a rotary move only. G93 Inverse Time ON or G94 mode. Sometimes a Feedrate must be present on each Line of code or G93/G94 too.
    https://www.cnczone.com/forums/haas-...mastercam.html

  7. #7
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    Re: Possible Mach3 Bug

    Yes, the steppers are getting very hot, measured at 160 degrees F. Not much I can do about it short of putting cooling plates on them. Blowing air over them helped a little.

  8. #8
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    Re: Possible Mach3 Bug

    But, might have found the problem. Yes, humming and losing steps is an indication of the acceleration being too high, but, it runs fine for over 170.000 lines of commands. However, it did get stuck again on a completely different line, one that did not fit the previous pattern. It was just a 3/4 inch move on the z-axis without any move in the y or a. Sorry about the long explanation....

    So after another 6 hours of testing.

    The z-axis move is determined by the combination of the feedrate, the maximum allowed z-axis speed in mach3, the acceleration of z-axis, AND by the speed and acceleration settings for the y and a axis. However, since this is a 3d carving, it is also determined by the contours and depth of cut for the particular design.

    Smaller differences in depth of cut do not try to move the z-axis as much as a deeper cut adjacent to a shallower cut. Also, the z-axis move can also be slowed down by an associated a-axis move So for most of the carving, the z-axis only moves a little up and down and is tempered by the a-axis having to keep up. But when the a and y axis does not move, and there is a deeper cut due to the design, the z-axis is free to move at the maximum speed allowed by the setting in mach3.

    When I tested performance to determine the z-axis settings, it was just simple moves, and the drive could easily keep up. But under real cutting conditions, it was too aggressive. So when I lowered the maximum speed setting in mach3 for the z-sxis, the drive did not try to attain such a fast velocity, and it could keep up.

    The z-axis maximum speed in mach3 was changed from 150 ipm to 65. The acceleration was left the same. It still carves at an acceptable speed. The original setting was suitable for just simple starting and stopping of the z-axis. But in 3d carving, the action is an immediate reverse in direction after the stop. that reverse action seems to put a larger load on the motor, and then it lost the steps.

    This is what I found so far, it may prove wrong in later carvings. I know it does not explain all the symptoms seen, but I hope I found the problem. Spent days on this issue, need to get to do something useful on the machine!

  9. #9
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    Re: Possible Mach3 Bug

    Quote Originally Posted by George Brown View Post

    But in 3d carving, the action is an immediate reverse in direction after the stop. that reverse action seems to put a larger load on the motor, and then it lost the steps.
    That sounds exactly more like acceleration issues.

  10. #10
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    Re: Possible Mach3 Bug

    Quote Originally Posted by dazp1976 View Post
    That sounds exactly more like acceleration issues.
    Agreed, but interesting that it only shows up rarely in certain instances of movement.

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