Babystepping not being preserved between homing events.

oholmes

Hi,

I have recently encountered a strange problem with babystepping, the z-endstop position parameter, and the actual position of the nozzle.

If I run a print with the nozzle touching the printbed, alter the babystepping to say +0.4mm (yes this is extreme babystepping) to raise the nozzle to a perfect print height (printing a test square), then stop the print, rehome, and run the same print again, the nozzle will again be touching the printbed. This is counter to my previous experience with babystepping.

To try and work around the babystepping problem, I tried instead altering the firmware endstop position from 0mm to -0.4mm. This did not work, and so I tried -1mm, -2mm, +1mm, +2mm. None of this alters where the nozzle z position starts, which seems extremely odd!

As far as I am aware I have not changed starting gcode, duet firmware, or any of the physical printer since I started seeing this issue. I have not noticed any slippage of the z-axis (printer is a cartesian clone of the prusa).

I can only conclude that my own ability to debug this problem is beyond my current knowledge, so I ask kindly if anyone more experience knows how this could have happened.

Current firmware: 2.0(RTOS) (2018-06-05b3)
Duet board: Duet WiFi 1.02 or later (bought it 2 months ago)
Start Gcode:
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
G1 Z15.0 F9000 ;move the platform down 15mm
G92 E0 ;zero the extruded length
G1 F200 E3 ;extrude 3mm of feed stock
G92 E0 ;zero the extruded length again
G1 F300
;Put printing message on LCD screen
M117 Printing...

This gcode worked correctly when I first obtained my Duet3d, but equally it may have accidentally worked correctly and still been bad start gcode.

dc42

Can you provide a sequence of GCode commands that reproduces this in a simple way?

sigxcpu

I've had the reversed experience. I've explicitly added babystepping reset in homez.gcode because it looks like it was added on each homing sequence, the bed having its 0 coordinate higher and higher after each print.

oholmes

@dc42 I will prepare a full gcode file including: homeall, print, babystep, abort, print.

Likely will be Thursday or Friday due to travel/work. Thank you for your reply.

@sigxcpu very interesting!