Direct drive extruder and Bowden extruder on one machine?



  • I’ve been wondering, could a Bowden extruder and direct drive extruder be used on one machine to load and feed the filament into the nozzle? I guess I’m trying to figure out why I don’t hear much about using both on one machine? Wouldn’t it be beneficial since you could have the best of both tools on one system?



  • The whole point of a Bowden is to avoid the weight on the head.
    The whole point of direct drive is to avoid the limitations of a Bowden.

    What is the end result you want? Forget which style of drive you want.

    Can you combine the two? Yes, but it makes the Bowden redundant. The closest is if you for some reason have a very long filament guide tube that imparts so much friction that you can't pull filament down it with just your extruder. Then you might have a second motor to 'pre-feed' filament. Stratasys printers do something similar just to load and unload filament (part of a design where you can't get to the filament to feed it into the head even if you wanted to).

    In my experience its better to have a shorter tube and a more powerful extruder motor, but there are times when an extra motor might make sense. And yes, if its right by the spool, it can be used to feed the filament all the way to the nozzle when you load a new spool (assuming your drive will feed right though).

    Its not common because the cost of the extra motor, filament drive and driver are more than its worth in most cases.


  • Moderator

    @theruttmeister said in Direct drive extruder and Bowden extruder on one machine?:

    The closest is if you for some reason have a very long filament guide tube that imparts so much friction that you can't pull filament down it with just your extruder.

    If that's the case, just get a tube with a larger ID.



  • @Phaedrux said

    If that's the case, just get a tube with a larger ID.

    Diminishing returns... cable chain, multiple tight radius bends, long total length, TPU. But its an edge case.

    The solution was to beat it to death with a huge motor and a drive that doesn't slip! (and shorten and simplify the tube run). Prints got suddenly got 50% heavier... turns out the old head was not putting out anything like what it was supposed to.

    But for most people, yeah, a decent diameter bit of FEP and a good spool holder is all you need.



  • @theruttmeister @1997alex I think there is one other (very specific) occasion where you might be combining bowden & direct drive - a single hotend Y-splitter multi-material printer where you need direct drive (e.g. to print flexibles, or because you hate bowden). I'm thinking multiple bowdens connecting through a Y-splitter (similar to the original Prusa MMU), then a single direct drive extruder actually pushing the filament through the hotend.
    In reality here, the bowdens are more like loading devices to swap the active filament, whilst the direct drive is doing the brunt of the extrusion. You'd probably want to have the bowdens at quite low currents in normal running in case they are out of sync with the main direct drive extruder.
    Of course, there are many other reasons why this might not be a great design (filament clogging, lots of extruders etc) hence I've not seen one in real life, though there was someone else on the forum that mentioned they were working on one a while ago...



  • @engikeneer

    You could argue the Palette falls into this category.

    And in fact you can use the Palette to load filament into the head. But they have encoders and switches to make sure everything stays in sync.
    Palette splices though, because un-loading and loading filament is slow, wasteful and failure prone.


  • Moderator

    @theruttmeister said in Direct drive extruder and Bowden extruder on one machine?:

    But they have encoders and switches to make sure everything stays in sync.

    😂

    Thanks for the laugh, I needed that.



  • You've lost me?


  • Moderator

    @theruttmeister Sorry, I thought everyone was aware how notorious the Palette is for getting out of sync with splices taking too long and the buffer running out and there being no sensor to detect this and then snapping the filament.

    wasteful and failure prone.

    That part is bang on though.



  • @Phaedrux
    Clearly we have had very different experiences of the Palette... I've build multi-input heads, and I've used multiple generations of the Palette.
    The development units had some issues. But I have found the production units to be reliable. I'd certainly pick one over any multi-input design I've ever seen.



  • Very interesting points. I’ve heard of the mmu from Prusa it looks good and is less than the pallete but I’m not sure the mmu is worth buying at $299. The printer I have has a long Bowden tube and it takes while to push filament through and wanted to know if a single extruder at the other end of the bowden tube would be of any improvement besides loading quickly(already using a direct drive), considering that there’s articles on Bowden vs direct drive extrusion just came to mind.



  • @theruttmeister
    I had a similar idea, taking the advantage of a nema 17 with high torque on the bowden side, and a small nema 8 (80-100g) as additional direct stepper? Maybe with a 3:1 or 5:1 gear ratio. The idea is to help the small nema 8, which alone would not work. Is it so creazy?

    Marco



  • @1997alex In answer to your original question but without getting into any debate about whether it's a good idea or not, yes you can do that and you would not be the first to use two extruders in a push-pull arrangement. Configuration wise, you simply define a tool to use two extruders and then set the mixing ratio to 1:1.



  • @deckingman
    Thanks Deckingman . I know I can configure two steppers to work in sync, but the question in fact is if it is a good idea or not and if there are specific issues with this configuration. As of now I'm using the flex3drive system but I found the worm gear very fragile (it's the second tyme I'm oredering replacements). The other option which I'm evaluating is to change the plastic worm gear with metal gears.



  • @Marco_76 My comment was addressed to the OP, not to you. However, in answer to your question of whether its a good idea or not, it depends on the usage case. If you have an extruder that doesn't grip the filament well, and if the incoming filament runs through a long tube which may or may not have bends and thus induces friction in the filament path, or if you use large heavy reels of filament which do not rotate easily, then a push-pull extruder arrangement will help. Personally, I use Bondtech BMG extruders (6 of them) mounted on a second gantry which tracks the hot end, and my (6) filament reels rotate freely, and I don't use PTFE tubes on the inlet side of the extruders, so a push-pull arrangement is not necessary in my usage case.



  • @deckingman
    interesting solution. Is there any picture or schema which show this?



  • @Marco_76 said in Direct drive extruder and Bowden extruder on one machine?:

    @deckingman
    interesting solution. Is there any picture or schema which show this?

    Shows what? Do you mean the extruder gantry? If so then I guess you want to know more about my CoreXYUVAB printer. Plenty of information on my blog and YouTube channels which are linked in my description.



  • @Marco_76 said in Direct drive extruder and Bowden extruder on one machine?:

    @theruttmeister
    I had a similar idea, taking the advantage of a nema 17 with high torque on the bowden side, and a small nema 8 (80-100g) as additional direct stepper? Maybe with a 3:1 or 5:1 gear ratio. The idea is to help the small nema 8, which alone would not work. Is it so creazy?

    Marco

    Not crazy... but I don't think you get much from that. A NEMA8, even with a gearbox, puts out such a tiny amount of torque that I don't think there's much benefit over a plain Bowden drive. But I've not tried it, so I don't really know for certain.
    Its also easy enough to use decently large X/Y motors and a direct drive NEMA17... unless you really really want to go really fast.
    Oriental motors make a really nice NEMA11 (actually not true NEMA bolt spacing... but anyway) with a 10:1 spur gearbox, its insanely expensive, but makes for a nice light direct drive extruder. Puts out ~42oz-in of torque. Its a bit long with that gearbox, but it works nicely.

    https://catalog.orientalmotor.com/item/stepper-motors-motor-only/legacy-pkp-series-2-phase-bipolar-stepper-motors/pkp223d15a-sg10-1

    I expect that the issue with a push/pull setup is going to be the stretch/compression in the bowden... if you have too much, the small motor may run out of torque. With the tube stretching/compressing to effectively absorb the extra torque from the larger motor.
    Because the motors are running in sync, you might not gain anything at all... in a perfect world you would want to 'pre-load' the bowden tube, so that 100% of the torque from the large motor is being used for extrusion.
    It might be that the natural 'spring' that is micro-stepping will absorb that variation.

    Its would be fun to design and try such a setup.



  • someone once linked a two-in-one setup with two bowden feeders and a direct feeder here on the forum, which is one application where I see this could be beneficial: decent control of the retracted filament that's not used, and nice short retracts on the print head.



  • on verrf there was a presentation from ldo about their motor for the orbiter extruder

    https://www.thingiverse.com/thing:4223085

    Gear ratio - 7.5 (new option 7.2)
    Filament pushing force 120Ncm - 12.4 Kg
    Filament acceleration up to 660mm/s^2
    Retraction speed: 60mm/s
    Overall weight is about 140g
    

    the stepper motor is 70g



  • @Veti

    Nifty.

    I'd be worried about the long term durability of what looks like printed gears in that gearbox...
    But I've bought enough LDO motors over the years to trust them (even if I would plan for those gears wearing away...)

    3D printing really has made custom gears the easiest thing in the world!



  • @deckingman Impressive, I've seen your videos on your channel. I finally made my two flex3Drive working but I will take it as next generation, when I want to modify again my COREXYU 🙂



  • @Marco_76 said in Direct drive extruder and Bowden extruder on one machine?:

    @deckingman Impressive, ...........................

    Most people say "crazy" - (and they are probably right) 🙂



  • It does make sense, I am using it right now.
    I have a light Nema 14 direct drive and a large nema 17 bowden.
    The whole point of that bowden is to feed the filament inside the printer enclose so the small direct drive doesn't have to work so hard to get the filament.
    They is one big problem with that, it is hard to get the ratio perfectly, a slight amount to low on the bowden extruder and after some hours of printing it will span the filament bowden the bowden and direct drive. A small amount to much and it will tangle inside the printer enclose.


  • administrators

    @dragonn said in Direct drive extruder and Bowden extruder on one machine?:

    They is one big problem with that, it is hard to get the ratio perfectly, a slight amount to low on the bowden extruder and after some hours of printing it will span the filament bowden the bowden and direct drive. A small amount to much and it will tangle inside the printer enclose.

    Presumably the way to fix that is to use a trigger or two setup to measure the filament tension and then as the tension increases, feed a bit more filament. This can either be adjusting a constant feed from the pusher (ie. M220 + 0.1% ) or a simpler option is a loop of filament that as the loop reduces to a certain amount the pusher pushes until the loop increases past a certain amount. AFAIK thats how (some) filament extruders manage the spooling function.

    Anything that relies on perfectly aligning extrusion rates of long print time is bound to be very difficult to calibrate.