Z Height map loading



  • Using 2.04RC1 (2019-07-14b1)

    I have established a BLtouch height and in config have
    G31 P50 X-22 Y-51 Z0.624
    Then do a bed mesh compensation probe. All apparently OK.

    After re-homing the Z height is reported as 4.90. No Tool is selected at this point.

    If in PanelDue I enable bed level compensation or use G29 S1. New Z height is now 5.00. The Z axis has not physically moved.

    I get the message...

    Warning: the height map was loaded when the current Z=0 datum was not determined probing. This may result in a height offset.

    I don't know what "not determined probing" means, or even the sentence.

    Is it saying it is at Z5 or not? Should I set Z to 0 then load the compensation?

    On a related matter if I do T0 P0 Telling it Tool 0 is present it reports Z6.5 if I then load Z map it reports Z5.
    Following this if I then do T3 P0 Telling it Tool 3 is present it reports Z4.9 if I then load Z map it reports Z6.6

    The values are not really important because I have G10 P3 X0 Y0 Z1.6 in config.

    The point I'm making is that in defining a different tool it appears the Z map has to be re-loaded is this so?

    Where is the best place to enable compensation?



  • please post your homing files and bed files as well as the config



  • 2_1564410379429_homeall.g 1_1564410379429_config.g 0_1564410379429_bed.g

    Thanks for your attention. Hopefully have attached files



  • is there a specific reason for using a z min endstop and a probe?

    my suggestion would be to remove the z min and let the probe determine z=0



  • In the Home position the Z probe is outside the bed area. Z probe used for bed leveling.



  • @st-taw said in Z Height map loading:

    In the Home position the Z probe is outside the bed area. Z probe used for bed leveling.

    That's exactly what the warning message is warning you about. Z0 should be determined by the Z probe, since it has to go and map the bed using the trigger offset to determine where Z0 is, but when you home the Z axis, you're using an endstop, which may or may not match up with what the probe has determined is Z0.

    It's typical to add a G1 X Y move to place the Z probe at bed center before using G30 to probe the bed to define Z0, then you can move the head back to whatever resting point you wish.

    It's at this point where the Z probe has determined the Z0 where you can load the saved heightmap in the homing file. Or in the slicer start gcode after the printer has been homed if you prefer to only load and activate it during a print.

    I notice you have G29 S1 in your config.g. This should be removed for the same reason. It's loading the heightmap before Z0 has been determined by homing.

    https://duet3d.dozuki.com/Wiki/ConfiguringRepRapFirmwareCartesianPrinter#Section_Homing_Z

    https://duet3d.dozuki.com/Wiki/Using_mesh_bed_compensation



  • Thankyou for your reply.

    I have read these links before, thought I understood, but will do so again and try and get to grips. Forgive me if being thick.

    I want/need to understand the relationship between

    G10 P0 X0 Y0 Z0 ; The tool offsets
    G31 P50 X-22 Y-51 Z0.624 ; The probe offsets
    M208 X0 Y0 Z-2.0 S1 ; Axis limits
    G29 S1 ; Load Height Map

    Which offset is the G30 S-2 affecting above if any.

    I assume there is no document/drawing that shows this?



  • I have removed G29 S1 in config.g as suggested.

    I have updated the bed.g file to include probing the bed before doing a bed compensation (as attached).

    I don't really want to probe the bed every time I print.
    So just to be clear in my mind. In start.g do I move the Z probe to the location as it learnt Z in bed.g above and then load the height map?



  • @st-taw said in Z Height map loading:

    So just to be clear in my mind. In start.g do I move the Z probe to the location as it learnt Z in bed.g above and then load the height map?

    I', not clear in my mind what you mean either. 😜

    At the start of a print, you should do some form of the following order of operations

    • Home all axis however you like
    • have at least 1 G30 probe at bed center to set Z0
    • run G29 routine, or load a saved heightmap.

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