High retraction length



  • First thank you in advanced for any advice , I have spent months due to my lack of knowledge in 3d printer building trying to get my dbot printer to work.

    It seems that I'm having to use a large number to get my prints to stop having blobs and zits in my print.

    Right now my retraction length is 13mm which is extremely high and acctually causes jams due to the filament retracting so far back.

    I assum this is from another cause but I'm not sure what? Is it stepper settings for extrusion ? If so can I make small adjustments to fix it without throwing everything out of wack?



  • If you are a Bowden User than you can try this:

    Max Retract Length = TZ length + (BT length / 250mm)

    (On the e3D V6 Bowden TZ length is about 2.5mm - 3mm)

    This is what i found yesterday in the Prometheus Hotend Wiki:
    https://www.distechautomation.com/pages/pro-v2-hot-end-guide#1.03



  • @AS-3D:

    If you are a Bowden User than you can try this:

    Max Retract Length = TZ length + (BT length / 250mm)

    (On the e3D V6 Bowden TZ length is about 2.5mm - 3mm)

    This is what i found yesterday in the Prometheus Hotend Wiki:
    https://www.distechautomation.com/pages/pro-v2-hot-end-guide#1.03

    Jumping in here, because that formula interested me. I did a quick calculation with it for my Rostock Max and that would put my retraction at 5mm, which seems pretty high to me.



  • Like all these things, it's just a rule of thumb and every extruder/hot end/filament/speed/temperature/pressure advance setting/stepper motor/voltage combination will be different IMO


  • administrators

    My rule of thumb is that retraction length should be about 1mm plus a little less than 1% of the Bowden tube length. This is with 1.75mm filament in standard 2mm ID tubing.



  • @KeeganB:

    @AS-3D:

    If you are a Bowden User than you can try this:

    Max Retract Length = TZ length + (BT length / 250mm)

    (On the e3D V6 Bowden TZ length is about 2.5mm - 3mm)

    This is what i found yesterday in the Prometheus Hotend Wiki:
    https://www.distechautomation.com/pages/pro-v2-hot-end-guide#1.03

    Jumping in here, because that formula interested me. I did a quick calculation with it for my Rostock Max and that would put my retraction at 5mm, which seems pretty high to me.

    Btw this is from the Prometheus Wiki maybe this calculation works better with there System.



  • @AS-3D:

    @KeeganB:

    @AS-3D:

    If you are a Bowden User than you can try this:

    Max Retract Length = TZ length + (BT length / 250mm)

    (On the e3D V6 Bowden TZ length is about 2.5mm - 3mm)

    This is what i found yesterday in the Prometheus Hotend Wiki:
    https://www.distechautomation.com/pages/pro-v2-hot-end-guide#1.03

    Jumping in here, because that formula interested me. I did a quick calculation with it for my Rostock Max and that would put my retraction at 5mm, which seems pretty high to me.

    Btw this is from the Prometheus Wiki maybe this calculation works better with there System.

    Yeah, I read through that link. Interesting stuff in there.

    Doing David's method puts my "calculated" retraction at about 6mm, which is even longer! Those lengths, whether right or wrong, seem like they'd suck too much molten plastic into the cooling area.



  • That's why I recently switched to a Lite6, as I don't print high temperature filaments. With the Lite6, you can retract whatever value you want without jamming it.



  • Thanks guys! I so far have tried the calculation and it seems to have worked. Im still getting a little blobbing but Im tweaking the extra restart a little to see if that helps. The jamming has stopped as well.



  • @KeeganB:

    …............................................................
    Yeah, I read through that link. Interesting stuff in there.

    Doing David's method puts my "calculated" retraction at about 6mm, which is even longer! Those lengths, whether right or wrong, seem like they'd suck too much molten plastic into the cooling area.

    Not really. It's certainly a fact that longer Bowden tubes need more retraction. The theory behind that, is that the filament buckles and twists inside the Bowden tube and 1mm in 100mm seems to be a not unreasonable value. So if you have (say) a 400mm Bowden tube and retract 6mm, then 4mm will be to "straighten out" the filament inside the tube and only 2mm will actually be pulled back from the nozzle. If there is any "play" in the couplings then that too can add to the amount of retraction needed. Typically the standard type of pneumatic couplings that are often used can have a couple of mm play if you don't use clips under them, so that could add another 4mm to what is needed. So adding it all up, a 400, Bowden tube with "sloppy" couplings could need as much as 10mm retraction in order to pull 2mm from the nozzle.



  • @KeeganB:

    Doing David's method puts my "calculated" retraction at about 6mm, which is even longer! Those lengths, whether right or wrong, seem like they'd suck too much molten plastic into the cooling area.

    I think perhaps David meant "1% of the bowden lenghth measured in centimeter". Bowden lengths on Delta's are most often mentioned in cm. That would put the retraction length at 1.6mm which is fine for E3D and HE280 hotends.



  • @DeltaCon:

    @KeeganB:

    Doing David's method puts my "calculated" retraction at about 6mm, which is even longer! Those lengths, whether right or wrong, seem like they'd suck too much molten plastic into the cooling area.

    I think perhaps David meant "1% of the bowden lenghth measured in centimeter". Bowden lengths on Delta's are most often mentioned in cm. That would put the retraction length at 1.6mm which is fine for E3D and HE280 hotends.

    Maybe, as that number seems much more reasonable.


  • administrators

    No, I meant 1% of the Bowden tube length. I use 4mm on my Ormerod (350mm Bowden tube) and before I enabled pressure advance I needed 7mm on my delta (60mm Bowden tube).


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