BLTouch very occasionally not deploying



  • Been having a very intermittent issue with my BLTouch, where maybe every few weeks it doesn't deploy, causing the head to crash into the build plate. It's rare enough that I get comfortable not checking and forget. Today it crashed hard enough to break the BLTouch pin (2 week wait for a new one 😕 ).

    Unfortunately, I didn't notice what state it was in (e.g. if it was in an alarm state), as I just cut power before any major damage happened.

    If it was a config issue, I'd have assumed it would happen more often. So wondering if there's other things I should check, or general things to do to improve things?

    • I don't have shielded cables for the BLTouch, so that's the first change I'll be making - Should I go for a 5 core cable, or a 3 core + 2 core, or will it not matter?
    • I'll modify my home*.g files to lower motor current for Z so that hopefully if it does happen again, it'll stall rather than break the hotend/bed.

    The only BLTouch pins I could find in stock were £9 each with 2 weeks delivery. I've found the BLTouch 3.1 (I have 2.1) in stock on much shorter delivery. Is there any appreciable difference? I can wait the 2 weeks for the pins, but would I gain much beyond a lighter wallet by being impatient?



  • @keyz182
    I think it's more related to a mechanical issue. You can try to remove and clean the pin.
    The other thing can be the set screw on top of the Bltouch.

    https://forum.duet3d.com/topic/11503/bltouch-randomly-stops-working/3?_=1588091319310



  • I'll keep that in mind when the replacement pins arrive. I doubt any amount of cleaning the currently snapped pin will help that cause! 😛


  • Moderator

    I'd probably spring for the new BLTouch. The pin may just be a bandaid to get a borked probe working/failing again.

    I don't think shielded cable will make much difference. I have my BLTouch cables running along side all the other print head cables (2 fans, heater, PT100, stepper) though the fans and heater and stepper are all idle when probing, so...

    Until you get your new probe you can change you M558 probe type to P0 which will allow for manual probing when G30 is called. So you'd get a pop up asking you to manually jog the nozzle to touch the bed.

    Also, for the future, it's a good idea to use M913 to drop the motor current during homing just in case there is a crash. That way the motors will stall before causing much damage.

    It's also a good idea to add a alarm release and retract command to the start of homeall and to the end of config.g just to get the BLTouch ready in case it is not. Ask me how I know.



  • @Phaedrux said in BLTouch very occasionally not deploying:

    Also, for the future, it's a good idea to use M913 to drop the motor current during homing just in case there is a crash. That way the motors will stall before causing much damage.

    Turns out I'm already doing that, I just never added a Z parameter (sensorless homing on X/Y).

    It's also a good idea to add a alarm release and retract command to the start of homeall and to the end of config.g just to get the BLTouch ready in case it is not. Ask me how I know.

    No need to ask, I should know myself. In fact, I had assumed I was already doing that, but I was not. 🤦


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