Bowden: an extruder off the print head

How Bowden works

The name comes from the Bowden cable, in which force travels along a flexible cable inside a tube. In a 3D printer it is the filament that slides along the tube: the extruder stands on the frame and pushes it through a long PTFE tube into the hotend.

The head therefore carries no motor and is much lighter. It can move quickly without the printer shaking, which mattered especially on older printers.

The drawbacks of a long tube

• Springiness. Filament in a long tube compresses and stretches a little. When direction changes, the pressure at the nozzle changes later than it should, and the inaccuracies show on corners.
• Retraction. The pull-back before a move has to be longer to have an effect at the nozzle (retraction), which raises the risk of stringing (stringing).
• Soft materials. Flexible filament easily jams in the tube.

Bowden and direct drive

Newer printers mostly use direct drive today, because it is simpler to tune and gives a more precise result. Bowden is found on older models and on some very fast printers, where the weight of the head is the issue.

What matters for a customer is that the difference cannot be seen on the finished part if the printer is well tuned. More important than the type of feed are the layer height, the infill and the material you choose when ordering.

When Bowden makes sense

Bowden is an advantage when the goal is very fast head movement or a large build volume, where a heavy head would cause vibrations. On simpler printers it is also cheaper, because the frame is under less strain and the head can be a simpler design.

It does need careful tuning, though. The tube must be as short as possible, run straight and be well secured, and retraction must be set for each material. With wrong settings you see strings and blobs on the walls (blobs), which is why direct feed is usually chosen on new printers today.