Bowden Extruder: Use, How It Works, and Materials

A Bowden extruder is a 3D printer material feed mechanism that pushes filament into the hot end through a long tube. The long tube connects the extruder motor to the extruder’s hot end. The feed mechanism that supplies material to the extruder can thus be mounted separately from the hot end. This setup reduces the inertial mass of the print head, which allows for either higher accelerations or lower-motor powers. Various filament materials are compatible with Bowden extruders, including: PLA, ABS, PETG, TPU, and many specialty and additive-heavy filaments like carbon fiber and wood fiber strands.

This article will discuss what a Bowden extruder is, including its uses, how it works, and the materials used.

What Is a Bowden Extruder?

A Bowden extruder is a filament feeding mechanism used in many fused filament fabrication 3D printers. The filament gets fed into the hot end via a flexible tube. A Bowden cable is a typical control mechanism with a flexible wire core running in a laterally flexible but longitudinally rigid tube. This design allows the force component (the extruder motor) to be mounted separately from the hot end. The filament feed motor is attached to the machine chassis rather than the print head, so it doesn’t add weight to the print head itself. As such, the head can make faster and more precise movements.

How Does a Bowden Extruder Work?

The drive mechanisms vary, using either a gear or pinch wheel to convert the rotation of the feed or drive motor into a linear progression of the filament. As the filament is pushed through the feed mechanism, it is delivered under compression into the Bowden tube. That pressure is countered by the resistance at the hot end where it is melted and dispensed.

The Bowden tube resists filament compression by keeping it confined. The filament feeds through since the tube is longitudinally rigid. It is normal for the filament to want to curve because of the compressive force applied to it. This causes the filament to press against the inside of the tube, causing extra friction. 

Why Are Bowden Extruders Used?

Bowden extruders separates the relatively heavy feed motor and gear mechanism from the moving nozzle. It reduces the weight of the moving components and improves the inertial response of the print head. This also keeps the heat of the hot end away from the extruder motor. 

What Are the Different Materials That Are Compatible With a Bowden Extruder?

Listed below are filament materials that are compatible with Bowden extruders:

1. ABS

ABS filaments are known for their tendency to warp and shrink if they cool too quickly. The long filament path exacerbates issues with filament retraction and pressure fluctuations, resulting in oozing, stringing, and poor flow consistency. ABS filaments benefit greatly from precise temperatures. The remote Bowden setup can cause temperature inconsistencies, so it isn’t very compatible with this material. 

To learn more, see our full guide on What is Acrylonitrile Butadiene Styrene.

2. PLA

PLA filaments generally work well with Bowden extrudersbecause it shrinks and warps less than most filament types. The longer filament path may still demand tweaks such as increased retraction distances to compensate for compression and prevent stringing and oozing. On balance, PLA's lower printing temperature and relatively low sensitivity to temperature fluctuations make it better suited for this configuration than other, less forgiving filament materials. PLA filaments are less prone to warping if the temperature is consistently controlled.

To learn more, see our full guide on PLA Filaments.

3. Nylon

Nylon filaments can produce good results with Bowden extruders. However, the material can create some problems. Nylon filaments in the Bowden setup experience a lot of friction when the tube path is long. Friction forces may deform the filament and make retractions more difficult. Nylon filaments also demand precision in temperature control so they don’t warp. This can be hard to achieve because of the laggy nature of the feed process. Users must experiment with retraction distance, print speed, and extruder temperature to achieve satisfactory results. Nylon filaments perform best with steady and reliable temperature control that minimizes warping and enhances intra and interlayer adhesion.

To learn more, see our full guide on Nylon Filaments.

4. TPU

Thermoplastic polyurethane filaments respond well to Bowden extruders. However, they can suffer some issues that require careful setup and parameter optimization. Since TPU is so flexible, the force applied by the extruder motor can become counterproductive, curling the filament inside the Bowden tube. A longer filament path means more friction, as the filament deforms and makes more contact with the Bowden tube. Curled filament also won’t retract consistently. TPU works best with precise temperature control since fluctuations make for more stringing and poor or irregular extrusion. 

5. PETG

Polyethylene terephthalate glycol (PETG) filaments can be effectively used in Bowden extruder setups. However, there are property and parameter considerations that can improve performance. They typically perform reliably in Bowden extruders due to their relatively stiff nature. This results in a lower tendency to curl and warp in the tube when pushed by the extruder motor. Still, the longer the Bowden tube, the more friction and elastic compression the filament will experience. That also complicates retractions, resulting in stringing or oozing. PETG filaments benefit somewhat from consistent temperature control, though the print quality doesn’t vary as much as in some other materials. 

To learn more, see our full guide on PETG Filaments.

6. Flexible Materials

In general, flexible filaments are harder to use in Bowden extruders. They tend to curl, leading to friction and compression in the tube. The elasticity makes delivery uneven and retraction less precise. The uneven flow also affects temperature uniformity, which can hamper adhesion within and between layers.

7. Composite Filaments

Composite filaments (those that contain additives like carbon fiber, wood, or metal particles) typically present considerable challenges when used with Bowden setups. They contact the tube, experiencing friction and resisting extrusion. Additive-laden filaments tend to have higher friction coefficients than pure ones. This results in filament deformation or jamming, particularly when abrasive additives are involved. You’re likely to see surges and shortages in the feed rate. Additives such as wood or metal particles present a higher risk of clogging than others.

Composite filaments typically need consistent temperature control to ensure proper adhesion, as the additives can reduce adhesion behavior and leave less room for variation. Smoother filament flow and more precise control will generally improve temperature stability, making for better-bonded prints.

What Is the Primary Function of a Bowden Extruder in the Context of 3D Printing?

All 3D printing filament extruders serve the same general purpose: they feed filament to the object being printed in a controlled manner and at the proper temperature for adhesion. Bowden extruders do so by pushing the filament through a tube that runs from the fixed extruder to the moving print head. This keeps the heavy extruder mechanism off the mobile head but can introduce more friction and elastic deformation to the feed process. 

How Does the Bowden Extruder Contribute to the Overall 3D Printing Process?

The Bowden extruder improves printing performance in some ways but also has a few drawbacks. Bowden extruders are most often used with flexible filaments like TPU or TPE. The system can improve the guidance and control of the movement of filament from the spool to the hot end when optimized and maintained in good functioning condition. In a remote Bowden setup, the extruder motor is stationary and mounted away from the hot end, reducing the weight of the print head. This can enable faster movements with great precision, resulting in improved print quality.

Does the Choice of Filament Impact the Effectiveness of a Bowden Extruder?

Yes, the nature of the filament can influence Bowden extruder functionality. Each of the many 3D print material options on the market exhibits different compatibility with a Bowden setup.

Flexible filaments like TPU or TPE (thermoplastic elastomer) typically require very careful adjustments and monitoring to prevent buckling or deformation in the filament path. Filaments that contain abrasive or high-friction additives like carbon fiber or metal particles can cut into the Bowden tube over time, leading to steadily increasing friction and irregular feed rates. Irregularity of filament diameter may cause jams or feed rate variations. ABS, PETG, and others require more precise and narrow temperature control to create smooth, well-bonded parts. The Bowden extruder's ability to maintain consistent temperature throughout the filament path is crucial for successful printing. This can be challenging since the feed path varies and elastic effects influence extrusion speed.

Bowden extruders work well with a wide range of filament materials. However, you may need to experiment with settings or even modify the mechanism to optimize its performance. 

What Are the Advantages of a Bowden Extruder?

The advantages of Bowden extruders are:

1. Removing the weight of the extruder from the printer head can allow higher accelerations in the transport mechanism.
2. Hot print materials are more thermally isolated from the print head, reducing heat-creep.
3. Lower print head height allows some printers to build taller parts.

What Are the Disadvantages of Bowden Extruder?

While the Bowden extruder does offer advantages, it has its downsides and scenarios for which it is ill-adapted. These drawbacks include:

1. Bowden extruders can struggle with flexible filaments because the long path introduces extra friction. Careful setup and good maintenance can partially mitigate this.
2. Since the feed is initiated far from the hot end, there can be a delay in filament response time due to elasticity in the feed, leading to less precise extrusion control.
3. Retraction can be challenging to control reliably due to friction and elasticity in the filament. 
4. Loading and unloading filament can be more cumbersome compared to direct drive setups.
5. Bowden extruders typically experience more wear and friction than other types, especially with abrasive filaments. 

How Fast and Precise Is a Bowden Extruder Compared to Other Extruders?

When correctly operating, a Bowden extruder setup’s main advantage is the reduction of moving mass at the print head. This allows for higher accelerations because the moving head’s inertia is minimized. 

Are Bowden Extruders Commonly Used in Applications Where High Printing Speeds Are Essential?

No. Bowden extruders are not commonly used in advanced high-speed printers. While they do reduce moving mass, they limit the precision of the printing process. Bowden-enabled print speed can hit an upper limit because of the irregular feed issues discussed above.

What Is the Difference Between Direct Drive vs. Bowden?

The two systems differ in some key regards that define their functionality and maintenance issues, including:

1. Direct drive uses a pinch wheel or gear filament feed situated at the print head and feeds directly into the hot end, with no intermediary stage or mechanisms.
2. Remote Bowden systems place the feed mechanism of the extruder in a fixed position far from the hot end. They employ a tube under tension to feed the filament under compression.

To learn more, see our full guide on Direct Extruders.

Summary

This article presented Bowen extruders, explained them, and discussed how they work and their various uses. To learn more about Bowen extruders, contact a Xometry representative.

Xometry provides a wide range of manufacturing capabilities, including 3D printing and other value-added services for all of your prototyping and production needs. Visit our website to learn more or to request a free, no-obligation quote.

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