How does slipping Bowden tube affect retraction or does it at all?

  • I have an Ender 3 Pro with upgraded Bowden capricorn tube. The tube will move approximately 1-2 mm during normal operation, though it will not come out of the coupler at all. I have read that the movement if unchanging (constant movement of 1-2 mm) can be compensated for with settings adjustment to avoid retraction issues such that it will extrude or retract "that much less"... I do not understand how this is possible...



    Im confused by comments that a slipping Bowden tube on the extruder side only, say by up to 2 mm, is "lost retraction"... I have this problem too with the Bowden tube only at the extruder end, not the hotend, and wonder if it is really an issue at all. Here's why...



    The filament is in direct contact with the gear and wheel of the extruder. If the Bowden tube is only moving in/out of the extruder end of the coupler, there are no "gaps" being created to cause leakage of the filament, etc on the hot end...As the extruder is either pushing or retracting, the filament inside the tube is still moving as much as intended regardless of the amount of play of the Bowden tube... no? therefore, retracting will not be affected at all, nor would the extruding process. Am I wrong and if so, can someone explain to me how this would be?



    Note, I can see that this movement may cause under-extrusion on the feeding side process, as the machine is expecting say, 0.5 mm extrusion, but then has to compensate (unknowingly) for the slipping out tube during the "push", so not enough gets "out", but should not affect the retraction amount as the filament is still being pulled directly from the gears/roller.



    Am I wrong and if so, can someone explain to me how this would affect the retraction along with the under-extrusion?


    Hi and welcome to SE.3DP :-)

    To prevent the tube from slipping, use a clip on the pneumatic connectors.

    It does have the clip, but the tube slips anyway. I have been looking at replacement of this part since it was like this out of the box for both "stock" creality part and the one supplied with the metal extruder and info suggests aftermarket connectors with metal teeth are the best fix.

  • The slipping does result in lost retraction distance. It does not result in underextrusion, lost material (except possibly via having insufficient retraction after the reduction), or anything like that.



    If your retraction is set to 6 mm, but the bowden pulls 2 mm into the coupler when you retract, those first 2 mm of filament motion do not pull the filament out of the hotend at all. The position of the filament relative to the tube (and thus relative to the nozzle) remains constant. After the tube can be pulled back no further into the coupler, the remaining retraction pulls the filament back through the bowden tube, for 4 mm of retraction at the hotend/nozzle.



    When unretracting, the reverse happens. The first 2 mm of extruder motion push the bowden tube out of the coupler, and don't move the filament relative to the tube (or the hotend). After that the next 4 mm push the filament through the tube and back to the nozzle orifice.



    The result is the filament ending up back exactly where it started, but having backed out only 4 mm from the nozzle, not the requested 6 mm.



    These numbers are just examples but probably about right. If you put the plastic clip on the pneumatic coupler, the slipping should stop, but you can also just increase retraction if the amount after the loss to slipping is not sufficient.


    The retraction is also delayed, since the first 2 mm (in your example) of movement do nothing, although they may result in a quick reduction of the extrusion pressure in the nozzle.

    @cmm: Yes, that's a great point. It doesn't matter too much for the way slicers normally use retraction, doing it synchronously before moving on with travel moves, but it would be a major problem if they did it concurrently with travel, and it would utterly break linear-advance.

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Content dated before 7/24/2021 11:53 AM