Delta Rail Friction Detection - A Challenge



  • A major cause of print failures on my Delta is a build up of debris in the carriage rails causing friction and eventually jamming.

    I could possibly use stall detect and a lot of current tuning to detect this but that would still only tell me that a problem has already occurred which, whilst better than nothing, still results in a lost print.

    Regular cleaning helps but the cheap Chinese linear rails I have seem to be dust magnets and can go from perfectly smooth to head smashingly rough almost overnight. There is also the issue of debris inside the carriages, stripping them down before each print just in case would be a nightmare.

    What would be really helpful, therefore, would be a way to profile the motor current whilst moving each axis to detect roughness before it becomes a problem.

    From other threads I think that directly monitoring the motor current might not be possible however the overall system current is available so could be used as a rough guide.

    basically the way I envisage it working is that the printer is homed and then each axis is moved in turn whilst monitoring the system current to both spot spikes and obtain a current profile.

    On a delta the movement would need to be split into smaller chunks to avoid moving the head outside of the print area but that should be fairly straightforward.

    Though my interest is primarily my Delta printer this feature would also be useful for more traditional arrangements as well.

    As usual, apologies if this has already been requested - I'll learn how to search properly one day - I promise.



  • I have some pretty cheap rails myself, but I'll be honest I've never noticed them becoming affected by run-of-the-mill house dust. What kind of environment is the printer running in? Do the linear bearings have seals? I only ask because I run a cabinetry CNC at work whose linear bearings are constantly buried in all manner of crap and they never seem to get rough.



  • Yeah, I’ve never heard of dust/debris being such an issue for linear blocks. It’s not a combo mill/printer or something, is it?


  • administrators

    @markdnd said in Delta Rail Friction Detection - A Challenge:

    What would be really helpful, therefore, would be a way to profile the motor current whilst moving each axis to detect roughness before it becomes a problem.

    You can go some way towards this already, assuming you are using the Duet WiFi or Duet Ethernet. Home the printer, run M122 to reset the stallGuard settings, reduce Z acceleration (M201), and command some Z movements over the whole Z range of the printer. Then run M122 again. The driver SG max values indicate the maximum motor load measured.


 

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