G28 ignoring Z-Probe X/Y Offsets

Question

I recently installed a SKR 1.3 Board with a 3DTouch-Probe on my Creality Ender 3 Pro. The probe works, G29 does its magic, but:

If i issue a plain G28, the hotend first homes X and Y like before the Z-probe. The probe is now next to, not above, the bed. As the next step, the printer is supposed to home the Z-axis. The probe deploys and Z starts to lower until it smashes into the bed, because the probe misses the bed (if I don't stop it, that is).

I configured X/Y offsets for the probe, but they don't seem to be honored when performing the G28 code.

If I home X/Y "manually" with G28 X Y, move the hotend with like G1 X45 Y10, then home Z with G28 Z it works fine.

What did I miss? Is this intended behaviour & the user has to take care never to issue a plain G28?!

Answer 1

You need to enable the constant Z_SAFE_HOMING (like: #define Z_SAFE_HOMING) in your printer configuration file (if you're using Marlin firmware that is). This will move the nozzle to the middle of the plate prior to lowering the nozzle by default:

#if ENABLED(Z_SAFE_HOMING)
  #define Z_SAFE_HOMING_X_POINT ((X_BED_SIZE) / 2)    // X point for Z homing when homing all axes (G28).
  #define Z_SAFE_HOMING_Y_POINT ((Y_BED_SIZE) / 2)    // Y point for Z homing when homing all axes (G28).
#endif

Answer 2

Use Z Safe Homing to avoid homing with a Z probe outside the bed area

According to Marlin firmware with this feature enabled:

• Allow Z homing only after X and Y homing AND stepper drivers still enabled.
• If stepper drivers time out, it will need X and Y homing again before Z homing.
• Move the Z probe (or nozzle) to a defined XY point before Z Homing when homing all axes (G28).
• Prevent Z homing when the Z probe is outside the bed area.

To Enable Z SAFE HOMING, In the configuration.h file search (Ctrl+F) for #define Z_SAFE_HOMING. By default, it will be disabled to enable it just uncomment the line