What is an extruder?

An extruder is the part of the 3D printer that grabs the filament and pushes it towards the nozzle. Without the extruder the filament never reaches the nozzle and your printer does nothing. The extruder makes sure the material ends up in the right place.

How does an extruder work?

An extruder has a small gear that grabs the filament. A motor turns this gear which slowly pushes the filament towards the nozzle. The faster the gear turns, the more filament gets fed through. The printer does this on its own, you don't have to do anything.

Direct drive and Bowden

There are 2 types of extruders, and the difference is where the extruder is located on the 3D printer.

Direct drive

With direct drive the extruder sits on the print head. The filament gets pushed straight into the nozzle without traveling a long distance.

This works a bit better with flexible materials, and there is less chance of problems with feeding the filament. The downside is that the print head is often heavier, which can make the printer a bit slower.

Bowden

With Bowden the extruder is mounted to the printer frame, so not on the print head. The filament then travels through a thin tube (the Bowden tube) towards the nozzle. This makes your print head lighter and because of that it can often move and print faster. The downside is that flexible materials are harder to print, and it can run into feeding problems a bit more easily.

For beginners it doesn't really matter which type you have, both work just fine with PLA.

What does the extruder do?

During 3D printing the extruder pushes filament through the nozzle. The nozzle heats it up and makes sure it comes out liquid and lands on the print bed. But the extruder also does the opposite, pulling filament back. This is called "retraction", when the printer moves from one point to another without printing anything, the extruder pulls the filament back a tiny bit. This is how the printer makes sure you don't get little blobs of filament on your print.

When does the extruder go wrong?

The most well known problem with an extruder is a clicking sound during printing. This means the gear doesn't have a good grip on the filament and can't push it through.

This can happen because the nozzle is clogged, or the print temperature is too low. Or even with brittle or too moist filament.

With these kinds of problems it's best to check the nozzle first, that's more often the problem than the extruder itself.

Do you ever need to replace the extruder?

Normally the extruder lasts a very long time, and replacement is rarely if ever needed. Especially if you are printing PLA or PETG. If you notice the filament isn't feeding properly and the nozzle doesn't seem clogged, then it might actually be broken. In that case it might be time to replace the extruder.