Prusa i3 MK3 - C Alibrate​ ​ Z

At the end of the X/Y calibration, the printer measures the reference height above
each of the 9 bed sensor points and stores the reference heights in nonvolatile
memory. During normal bed leveling, it is expected that the PINDA probe triggers no
more than 1 mm from the reference value, therefore the nozzle is not allowed to
move more than 1 mm below the reference value during the bed calibration.
If you moved the printer, you may need to re-run the Z calibration to sample new
reference Z height values reflecting the twist and bend of the table surface the printer
is sitting on. If that does not help, please verify, that the PINDA probe is aligned with
the sensor points on the print bed during the bed Z calibration. The alignment shall
be ensured by the automatic X/Y calibration routine. If the PINDA probe is no more
aligned during the Z calibration over time, it is possible, that a pulley is slipping or
something on the machine frame got loose.
3) Bed   leveling   failed.   Sensor   triggered   too   high.   Waiting   for   reset.
Similar to case 2). This time the PINDA sensor triggered more than 1 mm above the
reference height. Before doing anything else, make the Z axis level by going all the
way up and try again.
6.3.6 Calibrate Z
Calibrate Z is located in the Calibration menu. It is always done with the steel sheet on.
It should be performed whenever you move the printer to a different location. It saves the
heights of all 9 calibration points in nonvolatile memory. Stored information is used every
time mesh bed leveling is called during a print. When the measured values are vastly
different from the stored values, the print is canceled because it is a good indicator
something is wrong. Calibrate Z is a part of the routine Calibrate XYZ  so there’s no need to
run it after a successful Calibrate XYZ.
It is a good practice to run this procedure every time you travel with the printer or the printer
is shipped  the geometry might change slightly and cause an error.
At the start of the Z calibration procedure the printer homes X and Y axis. After that, Z axis
will begin to move up until both sides touch the printed parts at the top.
Please make sure the Z axis went all the way up and you heard a rattling sound as the Z
stepper motors skip steps. This procedure ensures, that 1) the X axis is perfectly horizontal,
2) the print nozzle is in a known distance from the print bed. In case the Z carriage did not
touch the end stoppers, the printer could not possibly know the height of the print nozzle
above the print bed and it could therefore crash into the print bed during the Z calibration
procedure.
The Z calibration procedure also prompts you to "Please   clean   the   nozzle   for   calibration.
Click   when   done."
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