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Installed bed leveling probe, now Z homing moves to center

3D Printing Asked by rgov on March 5, 2021

I installed a BLTouch bed leveling probe on my printer which uses Marlin 2.0.5.3.

Now the printer seems to be of two minds when it comes to finding the origin. Homing XY moves to the lower left as it always has, but homing Z moves not only to Z=0, but also to the center of the build plate. The printer knows this is (100,100,0) and is not mistakenly thinking it is (0,0,0).

This causes some issues such as now the nozzle wipe at the beginning of a print happens right in the center of where the print is supposed to be.

Is this expected behavior?

2 Answers

I had the same problem, solved it by inserting

// Move X and Y to 0 after homing
process_subcommands_now_P("G1 X0 Y0 F5000");

at the end of G28.cpp, just before ui.refresh();

This moves the print head to X0, Y0 and leaves Z untouched after the homing procedure. This way any oozing that might happen while the extruder heats up will be outside of the bed.

Answered by Raahs on March 5, 2021

This is a consequence of enabling Z_SAFE_HOMING:

Z Safe Homing prevents Z from homing when the probe (or nozzle) is outside bed area by moving to a defined XY point (by default, the middle of the bed) before Z Homing when homing all axes with G28. As a side-effect, X and Y homing are required before Z homing. If stepper drivers time out, X and Y homing will be required again.

Enable this option if a probe (not an endstop) is being used for Z homing. Z Safe Homing isn’t needed if a Z endstop is used for homing, but it may also be enabled just to have XY always move to some custom position after homing.

My default Cura start G-code contained this sequence:

G28 X0 Y0 ;move X/Y to min endstops
G28 Z0 ;move Z to min endstops

I changed this to

G28 ;safe homing
G90 ;absolute positioning
G0 X0 Y0 ; move to bottom-left corner for nozzle wipe

However any oozing will still happen at the center of the build plate, which is a problem.

Answered by rgov on March 5, 2021

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