Retraction issues 800mm bowden Bondtech BMG

  • I'm new to the duet wifi but built 5 printers with both marlin and smoothie.
    I can not for the life of me sort this out. I've been juggling acceleration jerk, retraction.
    Coast and wipe for a week and a half now. Of course different temps and filament and
    pressure advance. I'm using a bondtech bmg with genuine e3d v6. Also tried the v6 lite.
    Both Slic3r and simplify3d and slicer and firmware retraction Same results.

    My bowden tube is 800mm and I'm on the edge of giving up. Please help

    My config:

    This is the extreme, first print but ive added this to show the corners, this still persist no matter what i do, just not to this level of blobbing

  • What D value have you tried in pressure advance? I'm running D.4 on my pressure advance and I have a 650mm bowden tube with a E3D Titan extruder. That is with a .4 nozzle and ABS plastic. I am also running the latest firmware 1.21RC. My extruder acceleration is set at 1000.

    I have been getting great result with that set up so far. I will be trying a .8 nozzle tonight in a volcano configuration.

    "Edit" I also use 4.0mm retracts at 45mm speed. I have also used 60mm speed which worked ok too but may be hard on the extruder plastic gear.

  • You might want to list some of the settings you have tried.

    From the config.g you posted my immediate reaction is that it seems to be a low amount of pressure advance for the length of bowden cable you use.

    Did you try a little negative extra restart distance?

    As a starting point I would likely begin with ~4mm retract, 80mm/s retract speed 0.2 pressure advance, no wipe (unless it is PETG), no coast, no extra restart.

  • administrators

    Some suggestions:

    • Are the blobs are occurring immediately before retractions and travel moves? if so then they are probably mostly retraction-related.
    • Increase extruder max speed in M203 to 3600 (i.e. 60mm/sec), and configure 60mm/sec retraction in speed in your slicer, or in M208 if you use firmware retraction
    • 800mm is a long Bowden tube, and you will need to tune your retraction settings and pressure advance well to get good results
    • What retraction amounts have you tried? With no pressure advance applied and an 800mm Bowden tube I would expect you to need around 9mm retraction. Less if you use Capricorn tubing and/or pressure advance.
    • With a Bowden tube that long, Capricorn tubing may help significantly.
    • It's probably best to tune retraction using the Lite 6 first, because if you use too much retraction with the all-metal V6 you are likely to get an extruder blockage. When you have found a good combination of pressure advance and minimum needed retraction, you can try the same combination on the V6.
    • I suggest initially you use no pressure advance, to find the minimum retraction you need to avoid getting zits just before travel moves. When you have found that value, add pressure advance (try 0.2) and see how much you can reduce retraction before the zits reappear.

    HTH David

  • Probably unrelated but I think you have a small mistake in your config.g

    On your M203 command you dont have the X and Y values set. Ie

    M203 12000 12000 Z1200 E2500

    Should be

    M203 X12000 Y12000 Z1200 E2500

  • Ive been trying every retraction between 1 - 7mm but never tried anything higher.
    Im going to try that later today and see what happens, probably going yo buy some Capricorn tubing aswell.

    Ill update later, thanks

    Thanks Dadiy, i fixed that the other day, but probably was in a commented old setting that i didnt see.

  • I have a long bowden tube (>800mm) and swapped to capricorn tubing and now use 5mm retraction @ 75mm/s with a small amount of extra length on resume I think 0.5mm, before that my retraction was all over the place and I really struggled to get it tuned, the downside was the titan couldn't push the filament hard enough for the new tube so I had to swap over to the Bondtech QR which has been awesome.

    Have you considered where you're mounting the extruder? Can you get it closer in some way.

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