Bowden vs Direct Drive Extruder | Comparing 3D Printer Configurations

Have you ever wondered, “What is a direct drive and a Bowden drive extruder system?  How do these affect 3d printing?” This article will go over these two types of extruder systems.  First, it introduces some common terminology of 3D printer parts. Then it provides an overview of the basics of an extrusion configuration.  Finally, we review some of the strengths and limitations of each.

Terminology

To understand the direct drive and Bowden drive configurations, it is important to know these three common 3D printer parts and assemblies:

• Hot End/Hot End Assembly: A hot end assembly comprises mainly a nozzle, heat block, and heat sink mounted to the gantry of a 3D printer. The heat block and nozzle assembly are heated by a resistive-type cartridge heater.  The heat sink and the remainder of the hot end assembly are referred to as the cold end. While not cold per se, the heat sink separates the heat block from the remainder of the components and radiates heat away from the assembly.  For the purpose of this paper, we will refer to the hot end assembly by its name or simply by “hot end” for brevity.

• Extruder/Extruder Assembly: An extruder assembly comprises a stepper motor, hobbed bolt or drive gear, and idler mounted to either the gantry or frame of the 3D printer. The extruder comprises the motor, gear, and idler while the assembly adds to it the remainder of the components.
• PTFE Tubing: PTFE stands for Polytetrafluoroethylene, with its most famous variation being TeflonⓇ. This tube is usually connected to either assembly using push-fit connectors or fittings to provide a smooth transition from extruder to hot end.

Basics of An Extrusion Configuration

The extrusion system is arguably the most critical component of any 3D printer. On FDM printers, extrusion begins at the extruder assembly where filament is grabbed between the hobbed bolt and idler and pulled into the system. At this point, filament is either pushed to and through a proximately located hot end (Direct Drive) or directed through a PTFE tube to be guided to the hot end (Bowden). In Bowden systems, the PTFE tube is typically 2-3 feet in length.  Once in the hot end, the filament will continue to travel until it has softened enough to flow through the narrow nozzle (.35mm-1.0mm orifice), where it will become part of the 3D-printed object.

Common Extrusion Configurations

The previously mentioned Bowden and Direct Drive styles represent the two most common extrusion-style configurations. Hardware-wise, these two configurations can use a plethora of varying elements or they can be nearly identical with the only variation being a longer PTFE tube in the Bowden system. For simplicity, we will assume the hot end and extruder assemblies are identical from Bowden to Direct Drive.

Bowden Configuration

Strengths

The Bowden setup configuration is popularly known for its faster print speeds compared to Direct setup configurations due to its lower moving mass.  Specifically, the separation between the extruder and hot end assemblies enables a Bowden system to offload the mass of the extruder onto the fixed frame of the 3D printer rather than on the print head. This is important because constant acceleration and deceleration cause backlash on the gantry.  Such undesirable effects are then amplified once more mass is introduced to the moving body. This constant jerking movement tends to oscillate the hot end back and forth, creating imperfections in the printed part. Moving with less mass on the gantry decreases these vibrating instances and gives it cleaner movements.

Limitations

A major drawback when printing with a Bowden-style extruder system is the homogeneity of material variance that can be printed at acceptable resolutions. More rigid materials like PLA and ABS perform well with certain Bowden setup configurations but TPE, TPU, and other more flexible materials require more software tuning to produce merely satisfactory parts.

On a Bowden drive, three different conditions must be satisfied to print flexible materials.

• Retraction settings must be large (5mm+) to prevent unnecessary oozing while the hot end is traveling between printed sections.  The oozing has the potential to ruin the entire printed object.
• The PTFE tube connecting the extruder to the hot end must have tight tolerances in order to prevent kinks within the tube which may cause missed extrusions or buildups in pressure. However, selecting a smaller tolerance can prove problematic and more sensitive to variances in filament diameter.
• Finally, a hobbed bolt with a more unique profile must be used to provide the most amount of pressure from the extruder to the hot end. A deeper profile provides better grip around the flexible filament, thus providing the force necessary to drive the filament to the hot end without losing grip. A profile like this cannot be used interchangeably with all 3D printing materials because it would produce a crescent-like indentation on more rigid materials, hence changing the hobbed-bolt style when switching material types is more common in Bowden configurations.

Direct Drive Configuration

Strengths

Direct Drive extruders are the most popular type of extruders. A prominent advantage is the responsiveness that is inherent with Direct configurations because of the location of the extruder relative to the hot end. Given the smaller distance, extrusion and retraction commands are more immediate, thus creating a more stable material deposition control, which in turn provides higher resolution. This added control makes printing in flexible and other exotic materials more likely to yield better results and higher print quality.

Additionally, since there is minimal distance between the extruder and hot end, the force supplied by the extruder does not have to be as large, meaning two things: first, there will be less probability of slipping filament via the hobbed bolt as the extruder will be more gentle on the filament; second, a smaller stepper motor may be used to drive the extruder, thus creating a lower energy draw and less mass for the gantry.

Limitations

Direct Drive configurations add mass to the gantry which can cause more vibrations and backlash when printing at faster speeds than equivalent Bowden systems. The increased vibrations can cause more wobble and a loss of accuracy.  However, the print speed at which a printer with a Direct Drive configuration prints is often limited by other hardware assemblies or systems. For example, a Direct Drive extruder may be able to move faster than 100mm/s, but if the hot end can only heat and expel a certain amount of material at the time, that may become the limiting factor in the assembly.

Choosing The Best Configuration

There are three factors to consider when selecting the correct extrusion system for the application:

• Resolution-Time Correlation
• Resolution
• Material Diversity

In a recent study, “Direct vs Bowden Whitepaper”, Airwolf 3D performed significant testing regarding these three factors using two Airwolf 3D HD printers as well as two Airwolf 3D AXIOM printers.  The study aimed to test the resolution of both a Bowden and Direct Drive configuration at different print speeds with different material.

Conclusion

In conclusion, Direct Drive extrusion assemblies come out on top due to their ability to perform consistently and with a wide range of 3D printing materials, including flexible materials such as TPE and TPU. Even though Bowden configurations do have the ability for slightly higher printing speeds, that advantage is negated when print quality, material selection, and usability is factored in.   To delve deeper into this topic of Bowden vs direct drive, to learn more about settings and to see images and results from our recent tests, download our white paper below.