# Printer goes beyond the bed when auto leveling

I am trying to add auto bed leveling to my Prusa i3. When I run G28 my printer hits the X and Y end stops properly, then it assumes X=25, Y=99 position on the bed and performs Z homing, after which it stays there. The problem is when I run G29 then it starts following the grid points from this position and tries to go out of bed.

My settings for the grid are:

#define LEFT_PROBE_BED_POSITION 10
#define RIGHT_PROBE_BED_POSITION 140
#define BACK_PROBE_BED_POSITION 140
#define FRONT_PROBE_BED_POSITION 20


And travel limits are set to this:

#define X_MAX_POS 150
#define X_MIN_POS 0
#define Y_MAX_POS 150
#define Y_MIN_POS 0
#define Z_MAX_POS 220
#define Z_MIN_POS 0


I guess this might be relevant too:

#ifdef Z_SAFE_HOMING

#define Z_SAFE_HOMING_X_POINT (X_MAX_LENGTH/2)
#define Z_SAFE_HOMING_Y_POINT (Y_MAX_LENGTH/2)

#endif

• What should be added to your question is the offset position of the sensor to determine the correct sensor bounds (see e.g. How to set Z-probe boundary limits in firmware when using automatic bed leveling?). Note that the presented code is somewhat dated w.r.t. current Marlin configuration, but, if correctly inserted, the printer homes in the middle of the bed dimensions.
– 0scar
Jul 24 '19 at 10:06

I don't know how your firmware load handles G29 ,but here's a guess, based on information at the reprap wiki . Try using FBLR to force the travel limits.