Max Safe Z Axis Jerk Setting?

Discussion in 'Getting Started' started by garethky, Feb 12, 2020.

  1. garethky

    garethky Well-Known Member

    Joined:
    Oct 8, 2019
    Messages:
    82
    Likes Received:
    36
    I'm using mesh bed leveling and I was printing a thin walled test cube, 100mm a side. It printed with 2 vertical lines in one wall caused by some brief but audible pauses in X/Y movement.

    I read the G-code and the 2 pauses occurs within a move caused by a single G-Code line. Its a transit from x=50 to x=150. The line has E-steps. So none of the explanations I have seen on the Duet forums makes sense. The best explanation I have is the Jerk setting for Z being too low as described in: https://duet3d.dozuki.com/Wiki/Using_mesh_bed_compensation#Section_Troubleshooting

    So: what a safe max z-jerk for the motion system?

    I'm shooting to run my perimeters at 100mm/second (F6000). Infill at 200mm/sec (F12000).
     
    Nibbels likes this.
  2. garethky

    garethky Well-Known Member

    Joined:
    Oct 8, 2019
    Messages:
    82
    Likes Received:
    36
    The default setting is 8 and I tried 80. That seems to have made the artifacts go away. Not sure if there is a procedure to set this in some more scientific way that multiplying by 10.
     
  3. 1013D

    1013D Active Member

    Joined:
    Jan 17, 2020
    Messages:
    28
    Likes Received:
    3
    where do you change this? code in the config.g? can you post it?
     
  4. garethky

    garethky Well-Known Member

    Joined:
    Oct 8, 2019
    Messages:
    82
    Likes Received:
    36
    #4 garethky, Feb 14, 2020
    Last edited: Feb 14, 2020
    Nibbels likes this.
  5. garethky

    garethky Well-Known Member

    Joined:
    Oct 8, 2019
    Messages:
    82
    Likes Received:
    36
    The other thing I added is this line:

    M376 H10;

    https://duet3d.dozuki.com/Wiki/Gcode#Section_M376_Set_bed_compensation_taper
    This causes the mesh compensation to taper from 100% at the bed to 0% at 10mm up. So you aren't killing your Z axis for the entire print. To be sure this doesn't solve the stuttering but it should be a good setting for the tool changer. Its gantry is very rigid and doesn't really sag.
     
  6. Nibbels

    Nibbels Well-Known Member

    Joined:
    Dec 12, 2019
    Messages:
    165
    Likes Received:
    32
    Thank you for this thread!

    I remembered reading it when I saw the exactly same behaviour on my TC.
     
    garethky likes this.
  7. dc42

    dc42 Well-Known Member

    Joined:
    Aug 16, 2016
    Messages:
    467
    Likes Received:
    207
    As a very rough guide, jerk of 50000 to 100000 divided by the steps/mm for that axis @ x16 microstepping is usually OK. So about 30 to 60 for the Z axis.

    I just checked and the Z jerk is still set to 8 on my TC; but I levelled the bed using shims, so it does hardly any bed compensation.
     
    Nibbels and garethky like this.
  8. garethky

    garethky Well-Known Member

    Joined:
    Oct 8, 2019
    Messages:
    82
    Likes Received:
    36
    Thanks @dc42! I'll try dialing it back to 30.

     

Share This Page