Direct drive extruder and Bowden extruder on one machine?
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@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.
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@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.
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@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.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.
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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.
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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 140gthe stepper motor is 70g
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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!
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@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
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@Marco_76 said in Direct drive extruder and Bowden extruder on one machine?:
@deckingman Impressive, ...........................
Most people say "crazy" - (and they are probably right)
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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. -
@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.
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@T3P3Tony what kind of trigger do you have in mind?
I was something like that but didn't found yet how to actually do that.
