Initial moves before printing

  • So, finally started to get some prints. Not great, by any means, but at least I have forced a print or two off it.

    However, I have a lot of strange behaviour that I can't track down and stop. So the bed does this weird thing where it goes up and and down several times before printing. That's not in the gcode, so I'm assuming it's something in the firmware?

    Secondly, on finishing the print, it retracts the filament almost down to the extruder (it's a bowden set up). Again, this doesn't appear in the gcode as far as I can see, so I'm puzzled why it does it.

    Start of gcode:

    ;Filament used: 0.198559m
    ;Layer height: 0.1
    ;Generated with Cura_SteamEngine master
    M104 S210
    M109 S210
    G21 ;metric values
    G90 ;absolute positioning
    M82 ;set extruder to absolute mode
    M107 ;start with the fan off
    G28 X0 Y0 ;move X/Y to min endstops
    G28 Z0 ;move Z to min endstops
    G92 E0 ;zero the extruded length
    G1 F200 E3 ;extrude 3mm of feed stock
    G92 E0 ;zero the extruded length again
    G1 F9000
    ;Put printing message on LCD screen
    M117 Printing...
    G0 F3600 X69.254 Y82.176 Z0.3
    G0 X68.827 Y82.546
    G1 F1800 X69.254 Y82.176 E0.02396
    G1 X69.837 Y81.813 E0.05308

    End of gcode:

    G0 F7200 X99.17 Y88.071
    G1 F1800 X98.927 Y88.314 E198.55016
    G0 F7200 X95.116 Y88.468
    G0 X94.702 Y88.579
    G1 F1800 X94.423 Y88.575 E198.55257
    G1 X94.123 Y88.592 E198.55485
    G1 X93.853 Y88.578 E198.55711
    G1 X93.711 Y88.438 E198.55872
    G1 F1500 E192.05872
    M104 S0 ;extruder heater off
    G1 Z140
    G91 ;relative positioning
    G1 E-1 F300  ;retract the filament a bit before lifting the nozzle, to release some of the pressure
    G1 Z+0.5 E-5 X-20 Y-20 F9000 ;move Z up a bit and retract filament even more
    G28 X0 Y0 ;move X/Y to min endstops, so the head is out of the way
    M84 ;steppers off
    G90 ;absolute positioning
    M104 S0
    ;End of Gcode

  • Lots of information not in this post (such as the type of printer.) However, I'll take some guesses…

    The Z moving up and down might be related to G28 (homing the printer.) Take a look in homeall.g to see if there are Z movements in it.

    Retracting the filament: You appear to be using absolute extruder movements (M82) and the ending code has:

    G1 X93.711 Y88.438 E198.55872

    followed by...

    G1 F1500 E192.05872

    ...and then...

    G1 E-1 F300 ;retract the filament a bit before lifting the nozzle, to release some of the pressure

    If the extruder is in ABSOLUTE (not relative) mode, then "moving" from E 198 to E 192 is actually a retraction of 6mm. Then a movement to -1 is a retraction of an additional 193mm. In fact, E-1 is probably retracting the filament to the point where the extruder can no longer grip the filament to move it.

  • administrators

    As @garyd9 says, the Z movement is caused by homing X, Y and Z separately. If you replace the two lines G28 X Y and G28 Z by just one G28 line then if you have set up your homing files correctly, it will only move up and down once.

    @garyd9 is also correct in saying that the retraction at the end is caused by using G1 E-1 at the end when in absolute extrusion mode. Recent versions of Cura support relative extrusion, which we recommend you select. But if you must use absolute extrusion, insert either M83 or G92 E0 before that G1 E-1 command.

  • Ah, that all makes sense now. Many thanks to you both. I'll get editing!

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