Resetting the zero position of the X axis on a RepRapPro Mendel Mono My mono mendel 0,0 position is on the left of the bed, when the nozzle is at the position of the green dot in this image.



I would like to move that point to the left a bit, in order to print a slightly larger part (the bed has about a centimeter more space to the left). I know I can just allow negative values but I'd rather not to, for safety reasons.

However I cannot find where the offset of that point from the endstops (home position) is declared. There is no offset set in either pronterface or Slic3r, and unless my board came preloaded with different firmware than the one reprappro publishes, the *_HOME_POS variables in their Marlin repository are all equal to 0.

// The position of the homing switches. Use MAX_LENGTH * -0.5 if the center should be 0, 0, 0
#define X_HOME_POS 0
#define Y_HOME_POS 0
#define Z_HOME_POS 0


https://github.com/reprappro/Marlin/blob/master/Marlin/Configuration.h#L290

Any ideas how I should go about it?
I think the cleanest option is to move the X-endstop back about a centimeter to match, and then increase the size of the bed in both Slic3r's and the printer's settings.

You could also try using M206 to set a persistent offset after homing.