My PrintrBot z-axis got misaligned when I inadvertently left something on the printer bed after sending a new print to be printed. Did not realize till I heard the grinding noise. I cut the power but it was already too late. Upon restarting, the Z-home was almost an inch away from the bed.
Watched couple of videos on z calibration. Manually brought down the hotend till it was almost touching the bed and then fired up the auto leveling wizard. Tried a cube print first to see if it would turn out to be ok. The resulting cube was 0.3 short all around (from earlier reference cubes printed).
The M501 command showed that the Z axis was compensated almost -1.25.
< echo:Stored settings retrieved
< echo:Steps per unit:
< echo: M92 X80.00 Y80.00 Z2020.00 E93.50
< echo:Maximum feedrates (mm/s):
< echo: M203 X125.00 Y125.00 Z5.00 E14.00
< echo:Maximum Acceleration (mm/s2):
< echo: M201 X2000 Y2000 Z30 E10000
< echo:Acceleration: S=acceleration, T=retract acceleration
< echo: M204 S3000.00 T3000.00
< echo:Advanced variables: S=Min feedrate (mm/s), T=Min travel feedrate (mm/s), B=minimum segment time (ms), X=maximum XY jerk (mm/s), Z=maximum Z jerk (mm/s), E=maximum E jerk (mm/s)
< echo: M205 S0.00 T0.00 B20000 X20.00 Z0.40 E5.00
< echo:Home offset (mm):
< echo: M206 X0.00 Y0.00 Z0.00
< echo:PID settings:
< echo: M301 P22.20 I1.08 D114.00
< echo:Min position (mm):
< echo: M210 X0.00 Y0.00 Z0.00
< echo:Max position (mm):
< echo: M211 X152.40 Y152.40 Z152.40
< echo:Bed probe offset (mm):
< echo: M212 X25.00 Y0.00 Z-1.25
Took a wild guess and adjusted the Z-axis offset by 0.5
// Reset Bed probe offset (mm)
M212 X25.00 Y0.00 Z-1.20
// Save settings
Tried cube after the reset the offset, much better z-axis 3.01 to 3.02 all around.