Questions on Zeroing and bad mapping.

mendelevium

I wish to clarify some things about bed mapping and zeroing the heights.
to begin with I wish to confirm if these procedures are conducted in this order.

a) The probe is zeroed with G30 S-1 it is recommanded to repeat
several times to check for repeatabity.

b) The bed is probed by G29 S0 and the readings are stored in a mapping file in system.

my printer has a fine microswitch to home against at the top of the travel.
my config file I have the Z limits configured.

;AXIS LIMITS OF MINIMUM TRAVEL
M208 X0 Y0 Z0 S1
;AXIS LIMITS OF MAXIMUM TRAVEL
M208 X345 Y301 Z259.1 S0

my question is when the probe is zeroed, where is the adjustment correction value stored ?
This correction has to be repeated if the control is switched off?
or this has to be physically entered ? and if yes, where?

jay_s_uk

@mendelevium you need to zero the nozzle on the bed first using the paper method and G92 Z0. Then you measure the nozzle to probe Z offset using G30 S-1. This value then needs to be entered in G31 in your config.g
You can then remeasure the Z maxima endstop position using G1 H3 and adjust M208 accordingly.

None of the values are explicitly stored unless you ask them to be and even then, the values stored are limited. The docs on M500 tell you what can be stored https://docs.duet3d.com/en/User_manual/Reference/Gcodes#m500-store-parameters for everything else, edit the appropriate file

mendelevium

@jay_s_uk
Thanks for the clarification.

mendelevium

@jay_s_uk
M208 you mean?

jay_s_uk

@mendelevium said in Questions on Zeroing and bad mapping.:

;AXIS LIMITS OF MAXIMUM TRAVEL
M208 X345 Y301 Z259.1 S0

That M208

Phaedrux

The exact details on how to find your probe offset using G30 S-1 can be found here: https://docs.duet3d.com/en/User_manual/Connecting_hardware/Z_probe_testing

Then you can use G30 to accurately home the Z axis to find the Z0 point using the probe.

G29 uses a series of G30 probes are various points to make the map.

If you're using an endstop at the high end of Z travel for homing, use that first for course homing, and then use a G30 at the center of the bed to establish the true Z0. If you use only the endstop at the high end you're likely to have an offset and inaccurate z position unless you measure the distance from the bed at z0 to the endstop at zmax very accurately.