Print not centered if using G29 to auto-level

[PxT]

As discussed here: http://www.printrbottalk.com/forum/viewtopic.php?f=19&t=7822
and here: https://github.com/ErikZalm/Marlin/issues/732

[ei8htohms]

For me it seems to be related to an error with G28. It zeroes X, then zeroes Y, then zeroes Z to Y10 and calculates everything else from there. If I use G28 X0 Y0, G28 Z0 then it performs as expected.

[j-laird]

@ei8htohms - do you have non-zero values for X or Y in your M212?

[ei8htohms]

No. M212 X0 Y0 Z0.6.

[ArktekniK]

I have the same issue after flashing this firmware for my simple metal revision D printrboard.

Aside from the usual switching around of the motor's connectors, my M212 shows a positive 20 for the X offset. (I'm sure I saw this on the shipped firmware too)

As far as I'm aware, removing the offset is a thought of as a hacky way to solve the issue.

[ei8htohms]

Using non-zero values for X and Y probe offset is hacky IF you're using a probe. I'm using the nozzle to probe the bed so M212 X0 Y0 is correct in my case.

[ArktekniK]

Oh - I thought the offset was needed for the simple metal.
Well, I tried M212 X0 Y0, then a G28 X0 Y0, G28 Z0 and then finally a G29 and the bot correctly moves. Are the M212 settings stored in EEPROM? do they need an M500 or similar to store them?

[ei8htohms]

The probe offset is "needed" for the Printrbot Simple with the standard inductive probe. Having the correct offset will keep the bot from attempting to home in the Z direction when the probe is off the metal bed, something that could damage the bed, nozzle and/or coupler.

M212 will set the offset as your "current" value, but entering M500 will store it to EEPROM. If you do not store it to EEPROM then whatever values that are in EEPROM will become your current values on the next boot.

[PxT]

Not sure if anyone from the Printrbot side is following this, but the upstream bug (moved to MarlinFirmware#732) concluded that this is a misconfiguration.

The default values for the *_PROBE_BED_POSITION constants in this fork are causing the off-center problem.