July 10, 2013

What is a Bowden extruder?

One of the challenges when getting started with 3D printing is learning the terminology. Depending on your background, the various mechanical and project names may be complete gibberish. Fortunately, most of the ideas are pretty simple when you take a step back. For example, let’s look at the Bowden Extruder.

In its simplest form, when someone refers to a Bowden-style extruder, what they mean is that there’s a flexible tube guiding the filament from the extruding motor (cold-end) to the nozzle (hot-end.) In fact, you can convert a “traditional”, direct extruder into a Bowden extruder by separating these two parts and running a tube (generally made of teflon) between them.

The Direct Extruder

The direct extruder is more common, and it’s easier to explain the Bowden variant in terms of its differences. Let’s start with a diagram of a direct extruder (from the RepRap wiki):

320px-Extruder_lemio.svg
(Source: RepRap.org wiki)

The diagram above illustrates the workings of a typical, DIY extruder. A geared motor pulls filament, driving it into the hot-end for melting. The feature of note is that the extruder motor is directly above the hot-end (or at least very close.) A direct extruder will often look something like this:

yellow extruder
(Image source: flickr.com/photos/jabella/8965234122/)

The Bowden Extruder

For a Bowden extruder, we modify the diagram to be more like this:

bowden diagram

…and in practice, you’ll see something like this:

bowden extruder
(Image source: thing:29834)

…with the tube connected to the hot-end. The over-all look is like this (a Bowden-modified Printerbot Jr):

bowden printerbot jr
(Image source: thing:26963)

Why go Bowden?

There are pros and cons to both configurations, but the main reason people use a Bowden style extruder is to reduce the weight of the moving components. With the heavy stepper motor off in a fixed position, the hot-end can be moved with less force, generally allowing for faster speeds.

Where the name “Bowden” comes from

The Bowden extruder gets it’s name from its similarities to the Bowden cable:

bowden cable (Image source wikipedia)

If you’re familiar with a mechanical throttle cable or a wire bicycle brake cable, these are Bowden cables. Bowden cables are used to transfer mechanical action from one point to another. (Think brake-lever to brake-caliper.) With a 3D printer, a Bowden extruder uses its tube to guide a filament wire, transferring the force of the extruder motor into pressure in the hot-end. However, since the filament is a consumable, the mechanics aren’t quite the same. Unfortunately, I don’t know of a better name, and “Bowden” has traction, so that’s what we’re stuck with. Either way, you now know what it is.

12 Comments on “What is a Bowden extruder?

Patrick
August 12, 2013 at 11:44 am

Nice!
Exactly what I was looking for!
Do you have a hint for where to get the Teflon tubes?
Patrick

Reply
Erik
August 12, 2013 at 2:57 pm

If you’re in the States, mcmaster.com carries a variety in the “plastic and rubber tubing” section. There’s also a few suppliers listed on the RepRap wiki: reprap.org/wiki/Bowden

Reply
Shazza9
September 4, 2013 at 12:11 am

Search for PTFE tubing on eBay, what comes up is mostly PFA but it is effectively the same stuff.

Reply
Justin
March 10, 2014 at 8:50 pm

I think there is a typo in the last paragraph. Where it reads “brake-level” it should say, “brake-lever”.

Reply
Erik
April 8, 2014 at 8:39 pm

Thanks Justin! Typo fixed.

Reply
earthengine
April 22, 2014 at 12:33 pm

My mower have a broken throttle but the tube is OK, I removed the iron wire from the tube for something else. Can I use this tube? It looks like the filament fits it but I haven’t tried it on extruder.

Reply
Erik
August 18, 2014 at 5:54 pm

Well, that’s DIY ;-) You know, I’d be worried that the inside of that tube would be dirty, and thus might transfer odd things to your filament. Otherwise, why not?

Reply
Carl Mikkelsen
September 9, 2014 at 1:31 pm

How do Bowden extruders work with more “squishy” filaments, like Nylon and Ninjaflex?

I have concern that there will be a lot of windup needed to adequately pressurize the melt chamber.

— Carl

Reply
DarkAlchemist
January 26, 2015 at 9:59 pm

From what I have been told they don’t like Ninjaflex much at all as it is just too flexible.

Reply
Erik
February 26, 2015 at 6:53 pm

I gather that with the flexible filaments, you want as little gap as possible between the drive mechanism and the hot end; so yes, bowden isn’t a good choice for that. You may even want to use a different extruder design altogether.

Reply
Ivan Hoe
October 23, 2014 at 2:45 am

Hei Erik, thank you for this clear, easy to understand information on Bowden extruders.

Reply
Chuck
November 20, 2014 at 12:33 am

This is a great simple explanation of the bowden extruder. Thanks!

Reply

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