z axis not moving correct amount

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This topic contains 9 replies, has 5 voices, and was last updated by  mastersapo 7 months, 3 weeks ago.

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    Dave K

    So, I’m getting movement in this MPCNC build.  However, there seems to be a surprise that I don’t understand.

    First, the hardware:

    X and Y axes are using the stepper motors from V1Engineering

    Z is using a different one because V1 only had 4 and is now sold out.  The one it’s using has the typical 1.8 degrees per step.  The leadscrew is from V1 Engineering, therefore 8mm/revolution.  The motors are all 3 set for 32 microsteps.  The Marlin is essentially Ryan’s version, with a different Motherboard (MKS Gen L v1.0)  The line defining the steps is:

    #define DEFAULT_AXIS_STEPS_PER_UNIT { 200, 200, 800, 200 }

    By my calculation, (32 microsteps/step)*(200 step/Revolution)*(1 revolution/8mm) gives 800 steps per mm, as is being used.

    However, sending commands from the RepRap Controller

    (#define REPRAP_DISCOUNT_FULL_GRAPHIC_SMART_CONTROLLER) causes about half the correct travel on the z-axis.  In other words, I send a command to move 10mm and it only moves about 5 mm.

    Obviously, I could change the steps/mm, but why would this be necessary?



    Any chance your stepper motor is 0.9 degrees/step?



    Or perhaps you don’t have the correct number of steps selected with the jumpers for your drivers. You need all three jumpers installed to get 32 steps.



    @billsey – if he used less than 3 jumpers, he would get more travel rather than less per step, so I don’t think that’s it.

    The other thing that would be easy to check is that the leadscrew is 8mm/rotation.  Ryan does a great job with quality control of his subvendors, so I doubt that is it, but it’s easy to check.  Other than the stepper motor and the leadscrew, I think you’re down to recompiling and reflashing the firmware with the steps/mm settings you have above.


    Dave K

    The first thing I checked was the angular step size.  Specifications at Amazon are clear, but, there was a specification card with the motor.  I should check that too.  From Amazon:

    * Manufacturer Part Number: 17HS19-2004S1
    * Motor Type: Bipolar Stepper
    * Step Angle: 1.8 deg.
    * Holding Torque: 59Ncm(83.6oz.in)
    * Rated Current/phase: 2.0A
    * Phase Resistance: 1.4ohms
    * Inductance: 3.0mH+/-20%(1KHz)

    Physical Specification:

    * Frame Size: 42 x 42mm
    * Body Length: 48mm
    * Shaft Diameter: 5mm
    * Shaft Length: 24mm
    * D-cut Length: 15mm
    * Number of Leads: 4
    * Lead Length: 1m with connector
    * Weight: 390g


    As for the jumpers, the MKS Gen L board has jumpers in all three positions.  They’ve not been touched.


    Dave K

    Good idea to confirm the travel per rotation.  It IS easy to check.

    I also thought about connecting the z-stepper to the x or y driver, which is set for 200 steps per mm since it’s a belt.  That result should point to either the leadscrew or the motor.



    Try an M503 to see what your current settings are. If they are at 800 for Z then BT is likely right on the stepper being the 0.9° instead of the 1.8°.


    Dave K

    Well, this one is just going to be a mystery  I guess, at least for now.  When I went back and connected all the stepping motors, the movement on the z axis is now OK.  I literally didn’t change anything .. Simply went ahead and connected x and y as well as z.  Before, it had been z only.

    In fact  I would think that I had just been mistaken, but I had been able to reproduce the problem exactly multiple times.

    But, now it works   Don’t know why.  Moving on

    Thanks for the ideas.






    Easiest way I found to fix this is to take Actual distance / distance commanded and multiply that by your current z-steps / mm in firmware. I just had this issue with the new Rambo. Used a drop gauge and lowered z by 10 mm at a time, averaged, uploaded new firmware, checked again and by the 2nd time I had repeatable accuracy below what my gauge could measure.

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