What Is The Function Of The Extruder In A 3D Printer?

Find out what the important extruder is used for in a 3D printer

Whether your print succeeds or fails is often down to one component: the extruder. It is one of the most important parts of a 3D printer and is responsible for sending the right amount of filament to the hot end of the device. This is where it gets melted and extruded down in thin layers to create your print.

Some 3D users confuse the extruder with the hot end but these are not the same. The extruder is regularly referred to as the “cold end” due to the filament being cold as it moves through the extruder when traveling to the hot end.

There are two main types of extruders available:

• Bowden
• Direct

Even with these, there seems to be a lot of confusing information between the two. You may have heard or read that Bowden extruders are unable to handle flexible filaments and sometimes have too much stringing. You may have also read that direct extruders are too slow and generally have too much backlash.

If these statements confuse you, we are here to help. We are going to discuss the basics of a 3D printer’s extruder and find out the differences so you can decide, once and for all, which option is right for you.

Similarities between all extruders 

All extruders contain a motor. Desktop 3D printers tend to use NEMA 17 stepper motors. The 17 stands for a 1.7” x 1.7” faceplate. However, not all NEMA 17s are the same. They can either be geared, have a 0.9 degrees/step, a 1.8 degrees/step, and so on.

Different motors have different voltage ratings, varying current ratings, and come in a range of lengths. They can also provide contrasting amounts of torque. Although they can differ, none of these specifications make the extruder motor better or worse than another. The requirements from the motor for sufficient functioning usually depend on the setup of the extruder assembly as well as the printer. 

The filament drive gear grabs the filament and extrudes it through the hot end of the printer. Due to the wide range of extruder applications, these drive gears are not always the same. The most common two are:

• Small steel gears that are hobbed
• Hobbed bolts

“Hobbed” means that teeth or splines have been cut into it. The drive gears are installed onto the motor shaft while the bolts are usually powered by geared extruder motors.

Another mechanism that is in all extruders is the idler. This holds the filament up against the drive gear so it can be extruded through the printer’s hot end. PTFE tubing, bearings, rubber wheels, and printed plastics can all be used for this idler mechanism. 

The idler is vital for the correct amount of pressure can be applied against the printer’s filament or the drive gear. If too much or too little pressure is applied, it can lead to extrusion issues that can impede your printing quality and success.

Differences between extruders

Bowden extruders

Bowden extruders are not attached to a 3D printer‘s hot end directly. These are designed so a tube extends from the extruder’s body along to the hot end. This is known as a “Bowden tube.” More often than not, this is a section of Teflon or PTFE tubing. Here, the filament is kept in place by the tube and moves through this to the hot end.

Direct extruders

Unlike Bowden extruders, direct components are directly attached to the printer’s hot end. If we take the Lulzbot Mini extruder as an example, it is a geared, direct extruder that runs a 3mm filament. 

A direct extruder is not the same as a direct drive extruder as many would think. Instead, a direct drive extruder means that the filament drive mechanism is mounted directly to the motor shaft in the printer. Interestingly, both Bowden and direct extruders can be direct drive.

To decide which is the better extruder, we need to consider the strengths and weaknesses of both.

Bowden extruder pros:

• Bowden extruders do not have an added mass of the extruder body that rides on the hot end carriage. This includes the motor, idler, gear, etc.
• 3D printers that have a Bowden extruder can move and print very quickly, accurately, and more precisely than the same printer with a direct extruder.

Bowden extruder cons:

• Because of the reduced distance between this extruder’s idler and its hot end, there is a lag in the system. However, this can usually be adjusted for in slice settings or firmware adjustments.
• These extruders tend to have more friction on the filament. This is due to the extra distance it needs to travel when moving from the gear pinch point/idler to the hot end. Increased friction can make it more difficult to print flexible filaments.

Direct extruder pros:

• Direct extruders have a very short distance between the drive mechanism and the hot end. This results in improved responsiveness (less lag in the system) retractions and extrusions. Moreover, this requires less torque to extrude the filament through the printer’s hot end. Better responsiveness generally means better and cleaner prints with less stringing and oozing on the surface finish.
• It is easier to print with more flexible materials such as Soft PLA, TPU, and Ninjaflex for a wider possibility of prints. In general, direct extruders are more suitable for flexibles than Bowden extruders. 

Direct extruder cons:

• The mass of a direct extruder must be moved with the hot end because they are directly attached to the hot end. This results in a higher chance of backlash, frame wobble, and overshoot.
• The added mass with these extruders means that there is a larger motor current which generates intensified heat on the motors and motor drivers. This can lead to quicker wear and tear on these motors
• Not as accurate as Bowden extruders as direct extruders don’t accelerate or decelerate as fast.

What you choose depends on what you want to print and the type of printer you have. Do you want to print as quickly as possible or wait to maintain the utmost accuracy?

Whatever the case, extruders are essential to any 3D printer but neither is inherently better than the other.