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It seems that a Bowden extruder is the most used in all cheap 3D printers by far compared to Direct Drive that is very rare under 500 USD machines. But I haven't understood the reason, since in terms of hardware a direct drive doesn't seem to have any impact on price more than Bowden (correct me if I'm wrong).

Why?

agarza
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AndreaF
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2 Answers2

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As I understand it, there's really no good reason for this except "momentum". At some point in the not too distant past, a Bowden extruder was seen as an "upgrade" over direct drive, which required a bulky toolhead that was seen as limiting speeds.

(This perception was at best accurate only for delta and CoreXY machines at the time even, I think. As it turned out, Bowden doesn't let you print faster, at least not at any quality, because the nonlinear/hysteresis effects of the Bowden tube on the actual amount of material extruded can't fully be compensated with linear advance/pressure advance once you reach moderately high speeds. You can overcome this with the Nitram Bowden but good luck finding a cheap 3D printer manufacturer willing to put in that kind of custom part!)

Anyway, all the cheap printer manufacturers jumped on Bowden as a feature, and they're slow to develop any new designs rather than just making incremental improvements and production cost optimizations to existing ones.

Since then, direct drive designs have improved greatly, and the mass of the good ones has gotten so low that it's hardly a consideration anymore except on the most extreme agility-seeking printers (designs attempting 50k-300k acceleration). Everything should be direct drive, especially since it makes things so much easier for beginners (no difficult-to-load tube, broken filament in tube, loose fittings messing up retraction, etc.)

Teaching Tech has a video, oddly named Why direct drive is not automatically better than bowden tube, where he basically concludes that it is actually better, and goes over some of the history I've touched on.

R.. GitHub STOP HELPING ICE
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    Delta and CoreXY can benefit from the low mass to reach extreme printspeeds, if the hotend can offer enough flow. But low weight stepper motor solutions are a thing now, especially the hemera. – Trish Dec 22 '21 at 08:35
  • @Trish I wouldn't call the Hemera "light weight", the Orbiter, however, is a different solution (half the weight of the Hemera). – 0scar Dec 22 '21 at 09:27
  • @0scar compared to *other* solutions, it is. – Trish Dec 22 '21 at 09:42
  • Both Hemera and Orbiter are behind state of the art, which would be things like the Sherpa Mini or https://www.youtube.com/watch?v=vjFZiRV01ns – R.. GitHub STOP HELPING ICE Dec 22 '21 at 15:40
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Using a bowden extruder allows the manufacturer to place heavy components lower down on the printer frame. This lowers the center of gravity and reduces the amount of movement that the hot end creates when it tracks across the bed.

This allows the hot end to move\print faster without having to reinforce the printer's frame or to include higher quality belts\motors or dampeners.

Aaargh Zombies
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    This was the theory when it first became a thing to do Bowden extruders, but it really does not apply (then or now). The manufacturers in question are aiming for print speeds of 30-75 mm/s and accelerations of 500 mm/s² or so when the difference between Bowden and direct drive only starts to matter around 3-5x those speeds. – R.. GitHub STOP HELPING ICE Dec 24 '21 at 17:53
  • If you look at some of the entry level printers from companies like Creality and Anycubic you will see that one common design choice is that the print head is supported by only 2 struts. While the higher end printers have 4. If you were to put the weight of the extruder onto a two strut 3D printer is would wobble a lot more when it moved so you would need to further reduce the speed to make it stable. – Aaargh Zombies Dec 25 '21 at 17:52
  • Empirically, that's not the case. Even the massive official Creality direct drive conversion (and likewise the print-your-own adapters to move the stock E motor and extruder on top of the hotend) operates perfectly fine at the speeds their printers are advertised to go at. – R.. GitHub STOP HELPING ICE Dec 25 '21 at 18:14
  • Moreover, I'm not sure what you mean by "only 2 struts". At least on Creality printers and all the ones with similar design, you have 2040 extrusions on each side with 3 POM wheels pressed against them, which is more than enough to hold the weight. On machines with only a single side driven (single Z motor), you might get some extra problems with play at the opposite side when using direct drive, and this is already an area of problem for these printers, so maybe that explains somewhat why they don't go with direct drive. – R.. GitHub STOP HELPING ICE Dec 25 '21 at 18:16
  • Most entry level FDM printers have a print head that's attached to gantry, and supported by two upright struts mounted either side of the print bed, with the extruder attached to the side of one of these upright struts.. Higher end FDM printers tend to have one upright struct in each corner. Which means that they are more stable. – Aaargh Zombies Dec 25 '21 at 18:22
  • It's more a matter of what the kinematics dictate than trying to be "more stable". You can stabilize the Z axis of an E3-style bedslinger with diagonals down to the base of the machine if you want, but it's not going to make a difference until you reach very high Z, and it's not going to make a difference in the direction the direct drive extruder would be throwing momentum from its increased mass (X direction). – R.. GitHub STOP HELPING ICE Dec 26 '21 at 01:34
  • More mass = more momentum. – Aaargh Zombies Dec 26 '21 at 13:24