G91               ; relative positioning
G1 H1 X-600 F1800 ; move up to 600mm in the -X direction, stopping if the homing switch is triggered (first pass)
G1 H2 X5 F6000    ; go back a few mm
G1 H1 X-600 F360  ; move slowly to X axis endstop once more (second pass)
G90               ; absolute positioning