Z axis adjusting right before print starts

  • Hi all,


    I am noticing that right before the print starts, the print bed is dropping just a notch, totally messing up my manual bed leveling. (I don't have a Z probe)
    In my start code on my slicer (Simplify3D) I have it set to G28, then the last line is to push a bit of filament out to prime the nozzle.
    Nothing is telling Z to move. I have all offsets at 0.

    But after priming I can see and feel (putting my fingers on the lead screw) the bed dropping just a hint.
    I end up having to bump the bed back up with the Baby Stepping function in DWC all the way to -0.2mm to get the nozzle height right again.

    In my Homeall.g I have G92 Z0 as the last line.

    I even tried to compensate for it in the start code by adding G1 Z-0.2 and the bed still went down. I reversed it by changing it to G1 Z0.2 just in case I had my bearings wrong but it seems as if Simplify doesn't care. Still dropping.

    Any ideas?

    Thanks in advance…

  • administrators

    What you are seeing is normal behaviour. The first layer is printed with the nozzle higher than the bed by the first layer height. There will be a G1 command in the gcode file you are printing to do this, and if the nozzle is right on the bed when this command is executed, you will see the bed drop.

  • Hmmm….

    Ok, then I need some advice then. I thought I had the nozzle height adjustment thing down pat but apparently I don't.
    My first printer, (a Prusa clone) maintained the same nozzle height after homing.
    I always understood that manually setting the nozzle height using a piece of paper folded in two as a feeler gauge, between the nozzle and bed, then adjusting the bed height screws to get a perfect distance for printing. So when the print started, this manually adjusted height determined the print height, and the layer height was determined by settings.

    If I am understanding you correctly, I should adjust the nozzle height to be touching the bed completely, and the gcode will raise the nozzle, (or in my case, lower the bed) per the layer height I have entered in the slicer?
    I always assumed that layer height = extrusion rate + print speed.

    Educate me.

    BTW....I just ordered your Mini IR height sensor from Filastruder. I read that it works well with a glass bed, which is what I use.
    I am hoping it will take the aggravation out of adjusting the bed level.

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