diff --git a/Marlin/Marlin_main.cpp b/Marlin/Marlin_main.cpp index b7ad8f49ac..3321b8c433 100644 --- a/Marlin/Marlin_main.cpp +++ b/Marlin/Marlin_main.cpp @@ -2744,11 +2744,28 @@ inline void gcode_G28() { float x_tmp = current_position[X_AXIS] + X_PROBE_OFFSET_FROM_EXTRUDER, y_tmp = current_position[Y_AXIS] + Y_PROBE_OFFSET_FROM_EXTRUDER, z_tmp = current_position[Z_AXIS], - real_z = st_get_position_mm(Z_AXIS); //get the real Z (since the auto bed leveling is already correcting the plane) + real_z = st_get_position_mm(Z_AXIS); //get the real Z (since plan_get_position is now correcting the plane) apply_rotation_xyz(plan_bed_level_matrix, x_tmp, y_tmp, z_tmp); // Apply the correction sending the probe offset - //line below controls z probe offset, zprobe_zoffset is the actual offset that can be modified via m851 or is read from EEPROM - current_position[Z_AXIS] = z_tmp - real_z - zprobe_zoffset; // The difference is added to current position and sent to planner. + + // Get the current Z position and send it to the planner. + // + // >> (z_tmp - real_z) : The rotated current Z minus the uncorrected Z (since homing) + // + // >> zprobe_zoffset : Z distance from nozzle to probe (set by default, M851, EEPROM, or Menu) + // + // >> Z_RAISE_AFTER_PROBING : The distance the probe will have lifted after the last probe + // + // >> Should home_offset[Z_AXIS] be included? + // + // Discussion: home_offset[Z_AXIS] was applied in G28 to set the starting Z. + // If Z is not tweaked in G29 -and- the Z probe in G29 is not actually "homing" Z... + // then perhaps it should not be included here. The purpose of home_offset[] is to + // adjust for inaccurate endstops, not for reasonably accurate probes. If it were + // added here, it could be seen as a compensating factor for the Z probe. + // + current_position[Z_AXIS] = -zprobe_zoffset + Z_RAISE_AFTER_PROBING + (z_tmp - real_z); + // current_position[Z_AXIS] += home_offset[Z_AXIS]; // The probe determines Z=0, not "Z home" sync_plan_position(); } #endif // !DELTA