DIY 3D Printer from scratch – Bowden vs Direct Drive

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Bowden vs Direct Drive setups? Welcome to 3DPrinterChat.com, this article is part of the DIY 3D Printer from scratch. In this topic you will learn what is an extruder, what are the models and how they can affect the printing quality and speed.

 

One of the first things that come up when we are choosing the printer, is the extrusion method,  which usually are the bowden and Direct Drive  (a.k.a Direct Feed).

But for we understand what they mean, and whats the difference, we need to understand you must understand what is an extruder, how it works, and why we use it.

 

What is an extruder?

The extrusion device will work by pushing solid plastic (filament, pellets, or other), into a heated zone, so it will melt and get in the liquid state.

Since the extruder still pushing solid plastic, the liquid plastic will be compressed and leave through an output.

In the picture below we can see a industrial extruder, this is exactly the same used to fabricate the filament used for 3DPrinting

 

a industrial extruder, this is exactly the same used to fabricate the filament used for 3DPrinting

Source: http://www.mechscience.com

As you can see, the plastic enter in the solid form, as pellets (small bricks of plastic), and the dye (the pellets come in natural color, is a bit white and opaque.

The extruder screw will push the plastic forward and compress it (notice that the center of the screw gets bigger as it reach the end, this will help to eliminate air and make mix things better.

On the output there will be a constant line of plastic. The filament extruder will have a nozzle of 1.75mm or 2.85mm (approximately), and then, it will go through another process to assure the diameter and the right properties.

On 3d printing, the process is similar, but we don’t have the compressing screw, and we use a nozzle with a small hole (usually o,4mm) as the output device.

Now that you understood what is an extruder, and how it works (from overview), we can discuss which “pushing” method is best, the BOWDEN FEED or the DIRECT FEED.

Direct drive / Direct feed setup

You can identify a direct drive setup when the extruder motor is right above the heatsink and the nozzle. this setup has huge advantages over the bowden, but also disadvantages.

Check the picture below to understand how it works:

Bowden vs Direct Drive

Advantages:

  • It can print faster (as long as the 3D Printers structure can handle it).
  • Small retraction required (usually < 1mm).
  • its possible to print on flexible materials easier and faster.
  • Less/no oozing.

Disadvantages:

  • It will use a lot of space compared to bowden and also might be harder to assemble.
  • The extra weigh of the motor will cause more resonance on fast direction changes, and that might create .”ghosts” or vibrations, (this issue only happens on fragile structures, like most prusas or graber’s derivated, when using high speeds).
  • Does not require PFTE tubes or pneumatic couplers, making it cheaper.
  • It is possible to use a weaker / cheaper motor, 2.2kgf/cm² are already ok,  and bowden usually works best with 4kgf/cm².

*note:  kgf/cm² its an torque unit, it means how much kilograms of force it has, divided by the area.

Bowden setup

You can identify a bowden setup when the extruder motor is far away from the nozzle, and there is a PFTE tube where the solid filament will be pushed into, thus creating pressure into the hot zone, extruding plastic. The PFTE tube is often used because of its small friction coefficient.

Check the picture below to understand how it works:

Bowden vs Direct Drive

Advantages:

  • Reduced weight on the carriage, reducing the ressonance effect (ghosts / vibration on high speeds).
  • Compact and clean design, there is not much things on the carriage, making it more visually attractive.
  • Capable of running on higher speeds than direct drive setups.

Disadvantages

  • Since the  PFTE tube cannot have exactly size of the filament, the plastic will have some space to be compacted inside the tube, requiring more retraction to make the nozzle stop oozing.
  • The PFTE tube will get dirty or worn out, therefore the friction will increase, and it might cause failures on the printing.
  • Requires a more powerful stepper motor than the direct drive, which will to do the same work.

 

Bowden vs Direct Drive Comparisons

Lets compare some printings, with both setups. Please note: this might not be true for your printer if it has a solid structure, and a high quality motion system.

At the first two images. at the left side, we have a direct drive system, and at the right a bowden, This example can be used perfectly with Prusa clones and similars (as Tarantula TEVO, Prusa Original and Clones, 80% of aliexpress  FDM printers.

Bowden vs Direct Drive

source: http://forums.reprap.org/read.php?1,344659

Bowden vs Direct Drive

source: http://forums.reprap.org/read.php?1,344659

As we can see, the bowden setup produces higher quality prints and at a faster speed. making it the best choice for common and complex printings. But if you want to print with flexible or other special filaments, you should consider the direct drive.

One great thing about 3DPrinting, is that you can change the extruder setup easily, you just need to print the direct driver support, or the bowden support (in this case, also need to purchase the PFTE, but it is cheap).

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Also published on Medium.

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