Help: mesh compensation ist not correcting right



  • @stewwy
    Thank you - where can you see the twist? The Sheet is a magnetic sheet - it wasn't maybe hit exactly to the end. And could this encounter such an effect? The right side is about 0.03 - 0.04 too deep overall...


  • Moderator

    @tom_Nbg said in Help: mesh compensation ist not correcting right:

    When I home all axis and hit G32, then the home-z will change, do I have to re-home z then again

    You haven't posted your homeall, so I don't know exactly what G28 is doing for you, but typically, you'd want to do a single G30 at the center of the bed after correcting for the tilt, since changing the tilt will slightly change the Z position.

    Does running G32 (bed.g) correct for the tilt completely after a single run? Or do you have to run it multiple times to get a good leveling?

    After the tilt is corrected completely, the G29 heightmap should be regenerated at least once. It can be reloaded afterwards provided the tilt can be corrected reliably.

    It's also possible that you have tilt on the Y axis. Correcting tilt on the X axis obviously won't solve that. But a G29 heightmap should.



  • @Phaedrux

    my homes are:

    ; homex.g
    ; called to home the X axis
    ;
    ; generated by RepRapFirmware Configuration Tool v2.1.8 on Mon Jan 20 2020 21:22:54 GMT+0100 (Mitteleuropäische Normalzeit)
    G91                ; relative positioning
    G1 H1 Z5 F180
    G1 H1 X5 F1000     ; move slowly away 
    M913 X30           ; lower motor current to 30% for senserless homing
    G1 H1 X-260 F2000  ; move quickly to X axis endstop and stop there (first pass)
    G1 X10 F1000        ; go slowly back a few mm
    G1 H1 X-260 F2000  ; move to X axis endstop once more (second pass)
    M913 X100          ; Rise motor current to 100% again after sensorless homing
    G90                ; absolute positioning
    G1 X15 F1000	   ; go to X=15
    
    ; homey.g
    ; called to home the Y axis
    ;
    ; generated by RepRapFirmware Configuration Tool v2.1.8 on Mon Jan 20 2020 21:22:54 GMT+0100 (Mitteleuropäische Normalzeit)
    G91                ; relative positioning
    G1 H1 Y-5 F1000     ; move slowly away 
    M913 Y30           ; lower motor current to 30% for senserless homing
    G1 H1 Y230 F2000  ; move quickly to Y axis endstop and stop there (first pass)
    G1 Y-10 F1000        ; go back a few mm
    G1 H1 Y230 F2000  ; move slowly to Y axis endstop once more (second pass)
    M913 Y100          ; Rise motor current to 100% again after sensorless homing
    G1 Y-10 F1000        ; go back a few mm
    G90                ; absolute positioning
    ;G1 Y10 F1000	   ; go to Y=10
    
    ; homez.g
    ; called to home the Z axis
    ;
    ; generated by RepRapFirmware Configuration Tool v2.1.8 on Mon Jan 20 2020 21:22:54 GMT+0100 (Mitteleuropäische Normalzeit)
    G90                   ; absolute positioning
    G1 X151 Y141 F3600    ; Move probe to middle of bed - first probing point, regarding Z-probe offsets
    G30                   ; home Z by probing the bed
    
    ; homeall.g
    ; called to home all axes
    ;
    M98 P"homex.g"           ; Call "homex.g"
    M98 P"homey.g"           ; Call "homey.g"
    M98 P"homez.g"           ; Call "homez.g"
    


  • @Phaedrux said in Help: mesh compensation ist not correcting right:
    ...

    It's also possible that you have tilt on the Y axis. Correcting tilt on the X axis obviously won't solve that. But a G29 heightmap should.

    Yes - this was my thought to use the heightmap... 😞
    I'm struggeling with this since 2 weeks around... and it is allways the right side, where the nozzle is too close and on the left, where it seems to be bit too far - as if would the meshmap left/right is mixed up...


  • Moderator

    @tom_Nbg said in Help: mesh compensation ist not correcting right:

    M574 Y2 S3 ; y max endstop

    Does this mean that when you're homing Y you move the bed towards the front of the machine?



  • @Phaedrux
    yes - because of my new carriage I need to home in front
    (but my issue was also in the old config with the old carriage - where I homed in the opposite direction)


  • Moderator

    Ok, just confirming that Y+ is moving the bed to the front (and therefore the nozzle to the front back edge)

    Just want to make sure you're still using a right hand coordinate system with 0,0 having the nozzle at the front left corner of the bed.



  • @Phaedrux
    ah - yes - 0,0 is left front...
    I give up for today 🙂
    my head is exploding... need a bit american horror story now 😉



  • @Phaedrux
    Hi,
    how do I configure or define what "bed type" I have? I mean:

    • if I have a "fixed x-gantry" and a "movable" bed (case 1) or
    • a "fixed bed" and a movable "x-gantry" (case 2). To illustrate see my both pictures below:

    The corrections to be made are allways in the opposite direction when running G32 if I have Case 1 or Case 2. And for mesh compensation the same. And it would explain, why on the right side, which is higher (the nozzle have to move up), it is getting close (because the correction is made in the opposite direction) and why it is on the left side in the opposite - and why the middle is mostly ok because it is more or less the pivot point?

    Could this be the problem or am I on a totally wrong way and didn't see anything else?

    IMG_1428.jpg
    IMG_1429.jpg
    IMG_1430.jpg



  • @tom_Nbg Could be, not familiar with magnetic beds, you should see any twist clearly when you look at the bed map side on, alternatively look at heatmap.csv in a spreadsheet to see the actual numbers, I believe it should be first point and last point in the file for xy0,0 and xy max or x min y max depending on where your probe does it's last probe.
    edit, answer to your 2nd post not the last post



  • @stewwy
    Yes: the measured right side in the heightmap.csv is "deeper" then the left side, but I see, that it is higher - so the values are mixed up... How to tell the printer that?



  • @tom_Nbg
    You have a Cartesian printer
    G32 is bed leveling using the 2 Z motors to level along the x axis. This does not as far as I know happen during printing it merely attempts to correct for errors before you start printing.

    G29 is mesh leveling this is a correction that occurs during printing to correct for hollows and bumps in your bed, although it can correct for an incorrectly leveled bed.



  • @tom_Nbg You can correct for it if you have bed leveling screws, otherwise use (G29)mesh leveling as it looks like you are pretty close anyway


  • Moderator

    @tom_Nbg There's no way of defining bed 'type', and it doesn't matter. So long as you have 'positive' Z moves that move the nozzle away from the bed (eg X gantry on Z moves up) or the bed away from the nozzle (CoreXY with bed moving down), and 'negative' Z moves move the nozzle towards the bed (either nozzle down or bed up), it's effectively the same to the machine coordinates and to the firmware.

    Ian



  • @stewwy
    I run G32 before I start a print. So if the meassured distance on the right side is different to the left one - then the motors are getting corrected independent - and if then I have my case 1 or case 2 as drawn, the corrections are made are wrong. Example: the right side is too high, the right screw has to rise up but the fw "thinks" the bed has to lower down, then the gantry get lowered down and the effect is, that the nozzle is even closer than it should.... and this is it what I have.... So the measured values just need to be inverted or something like this...?


  • Moderator

    @tom_Nbg If that's the case, you probably need to swap the motor wiring of the Z motors. Your M584 command will state two Z drives, eg M584 Z2:4, where Z2 is the 'Z' driver pins, and Z4 is the 'E1' driver pins. Your M671 command defines your leadscrew positions, but importantly, in the order you defined Z motors in M584. So M671 X-20:220 Y100:100 S0.5 defines the Z2 motor/leadscrew at X-20 Y100 and Z4 motor/leadscrew at X220 Y100. If you connect these the wrong way around, after probing, it will move the bed the wrong way, making the levelling worse. Check that the Z motors are each connected to the correct driver.

    See https://duet3d.dozuki.com/Wiki/Bed_levelling_using_multiple_independent_Z_motors

    If that isn't clear, post your config.g (which you should have done at the beginning) and perhaps a picture of your printer and/or wiring.

    Edit: overlooked config in first post!

    Ian


  • Moderator

    @droftarts said in Help: mesh compensation ist not correcting right:

    your config.g (which you should have done at the beginning)

    It's in the first post... 😉


  • Moderator

    @tom_Nbg said in Help: mesh compensation ist not correcting right:

    M584 X0 Y4 Z2:4 E3

    I think I see a problem. You have Y mapped to drive 4 as well as Z. You're missing a mapping for drive 1.



  • @Phaedrux
    no - it this was a copy/paste "rest" - and when I post it here I correct it to the inital state.
    y is on 1 (otherwise I think my z-axis would have crashed ;-). I swapped the z- and y-motor to to check if a driver has a problem. So my actual line is:

    M584 X0 Y1 Z2:4 E3    
    


  • I checked, if the correction is right and it is... I just put a 0.4mm spacer to the right side and the x-gantry was after G32 correct aligned to the bed... But my problem still exists... 😞 I've no further ideas anymore, what the problem could cause....


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