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Thread: Losing Steps

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  1. #1
    Join Date
    Oct 2010
    Posts
    27

    Losing Steps

    Hi Everybody,
    Does anybody know why a CNC router loses steps, and how can I fix the problem, I am running Aspire V4 and Mach 3.

    Kindest regards

    Terry

  2. #2
    Join Date
    Jan 2014
    Posts
    15

    Re: Losing Steps

    Might is because shaft coupling

  3. #3
    Join Date
    Apr 2004
    Posts
    5728

    Re: Losing Steps

    I doubt it has anything to do with the shaft coupling. If those slip, it's not a lost step error but a mechanical problem. Lost steps are typically caused by pushing a stepper motor harder and/or faster than it can reliably go. This can be related to a mechanical problem like a sticky slide, so it's good to check for smooth motion without the power on. In Mach3, the first thing to try when combating lost steps is to reduce the acceleration (in Motor Tuning). Try cutting it in half, and seeing if that helps. If not, cut it in half again.
    Andrew Werby
    Website

  4. #4
    Join Date
    Oct 2010
    Posts
    27

    Re: Losing Steps

    Thanks Mate,
    I was a bit scant with my info. I only loose steps from the Z axis. I wonder if it because I was running the CNC too fast.I will check the couplings.
    Thanks mate for your reply
    Regards

    Terry

  5. #5
    Join Date
    Oct 2010
    Posts
    27

    Re: Losing Steps

    Thanks Andrew,
    I think you are spot on. I will try that to day.

    Many thanks again

    Terry

  6. #6
    Join Date
    Jun 2010
    Posts
    4252

    Re: Losing Steps

    Another reason (beyond purely mechanical connections) for losing steps only on the Z axis is because the spindle power cable is running next to the Z axis encoder feedback cable. Noise pickup can be a but horrible there. You may need to separate them.

    On the other hand, if the Z axis always drifts downwards (or upwards), then you may have a totally different problem, which may sometimes (not always) involve acceleration settings. Whether you are using a stepper or a servo on the Z axis also matters.

    cheers

  7. #7
    Join Date
    Oct 2010
    Posts
    27

    Re: Losing Steps

    Thanks mate,
    I will certainly check out the wiring situation. The Z axis is driven by a step spindle (4HP) and so far only drifts upwards. I have slowed down the stepper to see if that helps. I will trying cutting the model again to day. It takes about 6 hours to cut this model so only using waste material until I solve the problem.
    Once again many thanks for your input

    Regards

    Terry.

  8. #8
    Join Date
    Jun 2010
    Posts
    4252

    Re: Losing Steps

    Hi Terry

    The Z axis is driven by a step spindle (4HP) and so far only drifts upwards.
    Oh dear, that is always hard to solve.
    You said it's a stepper motor on the Z axis? OK. IF (if) you can do this, it would be super interesting to run the following experiment. However, the steps assume that you have a 4-wire stepper motor.
    Reverse ONE winding. ie, swap A and A'. This will reverse the direction of rotation of the stepper motor.
    Flip the DIR Active state in Mach for the Z axis. This will correct the direction reversal.
    Run some tests to see which way the axis now drifts.

    If it now drifts downwards, that implies that there may be noise on either the Dir input line or somehow on the encoder lines.
    If it still drifts upwards, then the accelerations may be a problem.
    If it stops drifting ... start machining?

    If the stepper motor is different - 5 phase, or centre tapped, the steps differ slightly.

    Btw - 4HP stepper on the Z axis motor???? That's a bit unusual.

    Cheers

  9. #9
    Join Date
    Oct 2010
    Posts
    27

    Re: Losing Steps

    Hi Mate,
    The Z Axis is a 4HP spindle motor. 4 pairs or 8 wired. I am unable to send you photos within this forum, but if you were to send me your email address I will enclose photos. I built my CNC router from the ground up.with very little electronic know how.This is probably the problem! Not too bad I guess for a 68 year old. The reason for the 4HP Z axis spindle is that I can use up to 1/2" shank router bits. My live cutting table measures 900mm by infinity (lenghth). I am able to carve full length doors.

    Regards
    Terry

  10. #10
    Join Date
    Jun 2010
    Posts
    4252

    Re: Losing Steps

    Hi Terry

    I will PM you separately for email. But you CAN post pictures: use the image icon third from the right at the top bar.

    We do have some confusion here over axes and motors. I think maybe you are mixing up the Z-axis motor and the spindle motor?

    I can use 16 mm end mills with my 500 W Baldor DC motor.

    cheers
    Roger

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