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):
(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:
(Image source: flickr.com/photos/jabella/8965234122/)
The Bowden Extruder
For a Bowden extruder, we modify the diagram to be more like this:
…and in practice, you’ll see something like this:
(Image source: thing:29834)
…with the tube connected to the hot-end. The over-all look is like this (a Bowden-modified 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:
(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-level 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.