Mechanical bed setup with IR probe.

Hardware: Ramps 1.4, Arduino Mega 2560.
Mini Differential IR height sensor
Firmware: Marlin RC-6

As far as I can tell all hardware / firmware is working as it is suppose to. It is my understand of the setup of this hardware that is in question.

After using a Printrbot printer for a while I modified it and it is working fine but I wanted something a little more stable and hopefully with a level bed.

So I built a new one. I've been able to calibrate X, Y, and extruder ok but am having trouble getting Z off sets properly set.

The bed on this printer uses glass with a top later of PEI. The bottom side of the PEI is painted black so that the IR sensor will work with it. I am not sure if the IR sensor is working off the top surface of the PEI or the painted bottom of the PEI. I suspect that it is the bottom painter layer it is reflecting off of. This would mean that the actual print surface is 1mm higher than the reflective layer. I would think that this should alter the settings but I am not sure.

According to the IR instructions, preferably the bottom edge of the sensor board should be about 1.5mm higher than the bottom edge of the nozzle. Since the IR board is not adjustable the only way to adjust the height is to reprint the sensor mount with new dimensions to accomplish the proper height.

As best as I can measure the sensor board is 0.95mm higher than the nozzle. It also sets on the left side of the nozzle 30mm and ahead of the nozzle by 8mm. In the firmware I have defined the following settings.

#define X_PROBE_OFFSET_FROM_EXTRUDER -30 // X offset: -left +right [of the nozzle]
#define Y_PROBE_OFFSET_FROM_EXTRUDER -8 // Y offset: -front +behind [the nozzle]
#define Z_PROBE_OFFSET_FROM_EXTRUDER .95 // Z offset: -below +above [the nozzle]

I can't seem to find the correct Z (M851) settings. I seems that the nozzle is either too high or right on the surface.

Any thoughts or suggestions would be appreciated.

thank you.

1-Have the ir sensor high enough so it's not triggered.
2-Get the hotend to operating temp.
3-Lower the hotend until the ir sensor triggers.
4-Set Z to 0 using G92 Z0.
5-Then lower the hotend until a piece of paper slightly drags, and use the new z position on the LCD or via M114 for the z probe offset. If you have the EEPROM enabled, don't forget to update it.

The X & Y offsets don't have to be accurate.

Thank you stephenrc, that's a lot better.