BLTouch Offset Changes After A Print



  • Hi,

    I'm having issues with the Z Offset of the BLTouch. Everytime I print something, I have to re-calibrate the Z offet of the BLTouch and the difference is about (+ or -) 0.15mm each time. That's a huge difference for the first layer and due to this issue sometimes I have issues with first layer (too low or high).

    I'm sure that wiring is correct and cables are good. Also it is mounted well and it doesn't wobble on the mount.

    config file is as following:
    M574 Z1 S2 ; Set endstops controlled by probe
    M307 H3 A-1 C-1 D-1 ; Disable heater on PWM channel for BLTouch
    M558 P9 H5 T5000 A2 F120 ; Set Z probe type to bltouch and the dive height + speeds
    G31 P25 X25 Y35 Z0.88 ; Set Z probe trigger value, offset and trigger height
    M557 X25:275 Y35:240 S20 ; Define mesh grid

    Any idea why would this happen and how to avoid?

    Thanks!
    M



  • If you grab the heat block (while it's cold) and wiggle it, do you feel any movement? Are you sure there is no play in the print head and mount?

    Is the base of the BLTouch 8mm vertically from the nozzle tip?

    What is your bed surface like? Is it spring mounted?

    Try this for your M558

    M558 P9 H5 F100 T4000 A5 R0.3 S0.005 B1

    A little slower on the probe and travel move, and will pause for 0.3 seconds after travel to let the head settle before starting to probe. A5 will attempt to probe up to 5 times until 2 consecutive results are within 0.005mm of the trigger height. A2 won't actually work for that because the minimum and maximum number of probe attempts are the same, so if your probe is getting inconsistent results you won't be able to tell. And finally, B1 will disable the heaters during probing to eliminate any possible interference.



  • Thanks Phaedrux!

    I will be trying in 5 minutes when I cool the nozzle and let you know.

    I know that there is a movement when I wiggle the extruder mount but it's the whole carriage and rods, not only the mount.

    My surface is FilaPrint from Filafarm and yes I have Ultimaker springs.

    In the meantime I've changed the homeall to something you mentioned in one of your other posts.



  • @Phaedrux

    So, the base of the BLTouch is 10mm from tip of BLTouch when it's deployed and 6mm when retracted.

    Also, with the cold heat block, there is no play at all. It's the whole carriage that moves when wiggled.



  • @biradam 0_1540071882675_BLTouchZHeight.png

    8mm from the plastic base to the nozzle tip



  • @phaedrux

    Oops, sorry.

    It's around 8.4mm from base to nozzle tip.


  • administrators

    Which firmware version are you using? Some older firmware versions could cause a Z shift if you used a Z probe to re-home the printer while you had bed compensation enabled. The workaround was to cancel bed compensation before homing Z.



  • Ive reported this issue in other threads - knew something was wrong but couldnt get me head round how or why it was happening !

    What firmware do I need to be on to avoid this issue ?

    Since day 1 Ive been a Baby Stepping fool between every print ...

    My Custom Start Gcode in slicer - rehomes between prints - but also disables [ once ] the mesh grid comp before it homes - yet I still get this issue can be off as much as .22 ....


  • administrators

    @sputnikoc3d said in BLTouch Offset Changes After A Print:

    What firmware do I need to be on to avoid this issue ?

    See https://github.com/dc42/RepRapFirmware/blob/dev/WHATS_NEW.md for the firmware revision log.



  • @dc42

    I'm on the 2.02 RC3 already. I've just ordered IR Probe. Once I receive it, I hope the problem will be eliminated.

    I also realized that the offset changes when I switch the power off and on.

    Once I power on and set the offset, I can print with that offset a thousand times and the offset will stay same if the power was not switched off.

    While setting the offset, G30 S-1 would return the same number even if I retry for 10 times but after a power-off, the number changes.


 

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