Backwards Z G-Code

I am sorry if this is a stupid one, but it seems to not matter which settings I change, every time I slice my test object in Slic3r, the g code makes the bed go all the way to the bottom and start printing in mid air. I can finally get the thing to print the first layer by manually editing the first layer height to keep it up top, but looking at the 2nd layer, it wants to move it back to the bottom again.

I have tried inverting z movement in repetier, and then re-slicing in the hopes that was where it got that information from, but it seems to make no difference. I cannot think of what else to try and change.

Thank you for any help.


  • What z height does the gcode contain? Normally it starts with first layer height so it should be 0.3 or so. If going to 0.3 means mid air you might not have homed before. Without homing the printer does not know where x,y,z really are and assumes it is where it got started.
  • Hmm. I home all axes before I begin. It starts at X=0, Y=0, and Z=200. The slicer is set up for .2mm resolution, and the first layer is a little bigger so it's starting Z height is .250mm. It also seems to completely ignore the speed on Z. It always tries to zip it down too fast and overheats the driver.

    I have been manually editing the first few lines to change Z height to 199.750 and then deleting a 0 on the speed, just so it will start printing the first layer so that I could test it. It finally appears to be printing well enough, or close, and I'd like to figure out how to print more than 1 layer now...
  • The line I am changing reads:

    G1 Z0.250 F7800.000

    Which I am changing to :

    G1 Z199.750 F780.000

    In order to be able to print that 1 layer.

    I am guessing that I need to make repetier think that Z home is 0 and to go from 0 - 200 as the bed goes further down. I cannot find anything that makes it read this way though.
  • In case it helps anyone in the future, the solution was that everything was backwards but my test shape was rectangular so X and Y being inverted still looked the same. I had my endstops wrong too, thinking X and Y were mins but they were actually max, with a Z min.
  • Some slicers put same speed to z as with xy axis and rely on firmware slowing down z to max. allowed speed. Since it did not happen you should lower max. z feedrate in firmware so z moves do not loose steps.
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