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A Bowden tube extruder (like the stock one on an Ender 3) is known to have issues with printing the most flexible TPU, and with filaments that (either due to composition or condition) don't take well to too much retraction -- though the latter can be ameliorated somewhat with slicer settings. Direct drive extruders, on the other hand, by reducing the extruder to hot end distance to the practical minimum, greatly reduce the amount of retraction needed as well as the effect of filament compression and stretching.

One potential down side I'm aware of is that putting the extruder stepper and drive on the X carriage adds mass that the X drive motor has to both accelerate and decelerate; this could in theory have an effect on print quality, increasing ringing and overrun on the X axis (though this isn't generally a problem with the steppers used on the Ender 3 and similar printers).

What other reasons might there be to prefer a Bowden tube over direct drive?

Zeiss Ikon
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  • Would you keep the ptfe tube with a direct drive extruder as a filament guide? With the filament exposed, the X axis moves back and forth it pulls on the reel, rather than the reel advancing smoothly as the extruder pulls in the filament. No personal evidence it affects print quality, but I wonder if it’s a good idea. – ChinchillaWafers Jun 26 '21 at 15:55
  • The option certainly exists to keep a PTFE guide tube from near the spool to the extruder inlet side. My initial expectation was to rearrange the stock (top, behind the frame) spool location to be on top and in front of the frame; this would put it almost directly above the extruder's path along the X axis and motion would be in line with winding -- this would almost eliminate the need for even a hoop guide. – Zeiss Ikon Jun 26 '21 at 19:20
  • Have you considered the alleged benefits of a remote direct drive such as the Zesty Nimble? You get the advantages of direct drive without the mass of the stepper motor on the carriage. – fred_dot_u Jun 26 '21 at 20:31
  • Not familiar with that -- flex shaft from stepper to extruder? For an Ender 3, that's a bunch of stuff to buy and add, vs. a printable bracket to mount the extruder and its stepper, literally fifty cents worth of filament and a couple hours of printer time. – Zeiss Ikon Jun 28 '21 at 11:12
  • direct is noisier, slower, wears the stepper/belt more, and uses more power. – dandavis Jun 30 '21 at 04:03
  • Direct drive is always worth it, especially since it enabled you to use Linear Advance / Pressure Advance, which improves print quality much greater than the added mass might reduce it. If ringing is an issue, go with Klipper and its Input Shaper. – towe Jun 30 '21 at 07:17

2 Answers2

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There are really no reasons not to convert to direct drive, provided you use a good one. Many of the direct drive kits, especially the ones that reuse the existing giant NEMA-17 stepper, are not very good and have tradeoffs due to excessive mass on the toolhead, imbalanced mass, interference with frame reducing print volume, etc. The modern way to do direct drive is with a "pancake" stepper far smaller and lighter, and gearing between 3:1 and 6:1 reduction to get the needed torque - look at the Orbiter, Sherpa Mini, etc. - or even a remote direct drive.

Teaching Tech recently posted a video on this very topic, titled Why direct drive is not automatically better than bowden tube but then pretty much concluding that all the old reasons not to go direct drive no longer apply.

R.. GitHub STOP HELPING ICE
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  • So, essentially, "the only reason not to go direct drive is to avoid spending more." Because the advantage of literally just moving the existing extruder to the X carriage is that all it costs is a dollar's worth of filament and a couple hours of machine time -- plus the disassembly and assembly. – Zeiss Ikon Jul 12 '21 at 11:05
  • @ZeissIkon: Yeah that sounds about right. Just moving the motor/extruder has some of the disadvantages I described (not to mention the stock extruder just being really bad), and if you want to get a new motor, gears, hob, etc. you'll spend some more money. – R.. GitHub STOP HELPING ICE Jul 12 '21 at 17:00
  • So it's back to where everything else is -- if you want decent stuff, you can't afford it, and if you can afford it, you'll be futzing with it every other time you use it. – Zeiss Ikon Jul 12 '21 at 17:13
  • @ZeissIkon: The extruder is the main part I'd replace on an Ender 3 anyway to take it from being a mediocre printer to an excellent one. Don't shell out a lot of money for the light stepper; anything with the right RPM and torque specs is perfectly fine, and 0.9 degree is **worse** in this application. The most important thing is good hob and reduction gearing. – R.. GitHub STOP HELPING ICE Jul 12 '21 at 22:13
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Other than higher carriage mass as you already noted, the only other reason to not go with Direct Drive over Bowden is the higher level of maintenance required. In most cases Direct Drive will provide advantages such as increasing the maximum flow speed, enabling the use of Linear/Pressure Advance, shortening Retraction moves, and better resistance to obstructions in the filament path, and more reliable printing of flexibles as you have already noted. As well, A direct drive system would allow a less-powerful stepper motor to be used, which cuts down on the carriage mass problem.

craftxbox
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  • How does direct drive require more maintenance? You eliminate the need for replacing worn tube and fittings. – R.. GitHub STOP HELPING ICE Jul 10 '21 at 22:58
  • LA/PA can be used with Bowden or direct, but is more essential with Bowden. On direct you can almost get by without. – R.. GitHub STOP HELPING ICE Jul 10 '21 at 23:00
  • Sorry, Mustve had it backwards, I had seen somewhere that it's useless with bowden, maybe i'm just confused. Personally, I've had to do more maintenance on my direct-drive setup than bowden. – craftxbox Jul 11 '21 at 02:59
  • A bowden has hysteresis effects (tube takes time to return to unstretched state after being stretched) and some change in effective length with curvature (from toolhead moving) that make the LA/PA model insufficient to model the error fully. But unless you're sticking to print speeds so low you hardly need it, it's still better to run a bowden with LA/PA than without. – R.. GitHub STOP HELPING ICE Jul 12 '21 at 17:02