Swapping Filament

Discussion in 'Tool heads & ToolChanger' started by Spoon Unit, Sep 2, 2019.

  1. Spoon Unit

    Spoon Unit Well-Known Member

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    I'm curious if I'm just doing something wrong here, but it's the single most frustrating thing with the machine at present. Has anyone crafted a reliable happy solution? I think I'm very shortly going to end up with a very short piece of PTFE in the extruder, which the main tube feeds into. Any other ideas?

    I've currently got two macros for feeding and removing the current filament.

    Remove (Run after Tool selection)

    G0 E5 F200
    G0 E-35 F2750
    G0 E-750 F500

    Refeed (Run once filament visible above the Titan)

    G0 E730 F500
    G0 E40 F200
     
  2. Spoon Unit

    Spoon Unit Well-Known Member

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    So, in the end I did exactly as above.

    [​IMG]

    I've cut a 20mm piece to push into the bottom of the Titan. When feeding a new filament, I push it all the way through the end of the feeder tube to reveal about 10cm. Then grab hold of the filament, insert into the shorter 20mm tube, push, and then push the idler back against the spring. This then immediately pushes the filament bast the hobbed bolt and up into the bowden tube. Then release, and use the wheel or a macro to complete the feed. The 'refeed' macro from above will need adjusting for your bowden tube. I accidentally cut one of mine to 750mm instead of 790mm. One the 750mm tube, this macro pushes the new filament from about 1cm above the bottom of the Titan, into the hot end, and then pushes enough through to clear the previous filament.

    I also created a chamfer on my PTFE entrances at all locations using a craft knife. There are three per tool. One at the point nearest the spool, one going into the 20mm tube here, and one just above it, above the hobbed bolt. This is what I mean ...

    [​IMG]

    If you do this, take great care not to allow any PTFE shavings to remain in the tube as they're going to happily cause a jam in the hotend. I find this chamfer really helps guide the filament in, and the main area you notice this is the entrance just above the hobbed bolt. Without the chamfer you'll have to search for this entrance more than you would with the chamfer.
     
  3. dc42

    dc42 Well-Known Member

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    Don't forget that one way to load filament into the hot end is to temporarily reduce extruder motor current, then use a G1 H1 E move to feed filament until the extruder motor stalls.
     
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  4. Spoon Unit

    Spoon Unit Well-Known Member

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    I had that thought yesterday for ram purging. I was doing it using my ears and tuning it that way, but using stall detection should catch it earlier. For feeding new filament with stall detection, aren't you assuming a cold nozzle, or is the combination of low current going to result in an early stall at the first sign of trouble?

    Will play with this.
     
  5. Spoon Unit

    Spoon Unit Well-Known Member

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    Failed to get any further with this. It's also hard to diagnose.

    I pinched this from a thread on the Duet Forum combined with feedback from @dc42 on that thread ....

    Code:
    ;M302 P1            ; enable cold extrusion
    M201 E1000            ; reduce extruder acceleration
    M915 P3:4:5:6 S3 F0 R1        ; set stall detection threshold
    M400
    M913 E20:20:20:20        ; set extruder motor to reduced % current
    M83                ; relative extrusion
    G1 S1 E800 F3600        ; move fast 500mm of filament
    M400
    M913 E100:100:100:100        ; set extruder motor to full current
    ;M302 P0            ; disable cold extrusion
    G1 E50 F300            ; extrude slowly 50mm of filament
    I was trying this with a heated hotend, and even with only 20% current to the extruder motors, I still got no jams. I played with the S setting on M915 from 10 to -3. Played with extruder current from 10 to 30. I eventually settled on R1 for M915 hoping to see some log content, but even with logging enabled I see nothing in the log. At one point I did alter the accelerations too in an attempt to force a jam, setting the acceleration low and the speed high. This resulted in no extruding, but also no log. So I'm quite perplexed. I need to re-work the whole thing again on a new day.

    This ought to be the best guide to this

    https://duet3d.dozuki.com/Wiki/Stal...ruder_stall_detection_during_filament_loading

    I'll have to start again at it on a fresh day, but happy to take someone else's results if they've manged to progress further than this.
     
    Olle Wreede likes this.

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