One of the most important parts of a 3D printer is the extruder. This pushes filament to the hot end to be melted and extruded. There are three key parts that all extruders share: a stepper motor, a driver gear, and an idler. While the components of extruders are all the same, there are two different types of extruders: Direct and Bowden.
The difference between Direct and Bowden extruders is the location of the extruder in relation to the hot end. Direct extruders, as the name implies, are directly attached to the hot end and are a part of the print head.
Since Direct extruders are located above the hot end with little space between them, a Direct extruder keeps the distance that filament must travel from the extruder to the hot end to a minimum. This leads to the main advantages of this style of extrusion.
Better Extrusion and Retraction
Since there is less distance for the filament to travel, extruding and retracting the filament becomes much easier. Essentially, the filament is more responsive to the extruder. This means that there is less stringing and oozing that occurs because of worse retraction and leads to a higher quality print.
In addition, the closeness of the extruder to the hot end means that less torque is required from the stepper motor than in a Bowden extruder. Because of this, the stepping motor does not need to be as large or as powerful as in a Bowden setup. However, a large motor can provide more power with a Direct extruder, which can be beneficial.
Wider Range of Filaments
Direct extruders are also able to effectively print a wider range of filaments, most notably, flexible and abrasive filaments. While flexible filaments can work with Bowden extruders, Direct extruders can print them more effectively. This is because a Direct extrusion system is more constrained.
However, the location of the Direct extruder also leads to its main disadvantages. The weight of the extruder on the print head can lead to several problems. Since the print head is constantly moving, additional weight to move around could lead to backlash, banding, overshoot, or frame wobble. Additionally, the size of the extruder can be disadvantageous for some 3D printers, as it makes up a majority of the print head.
The opposite of Direct extruders, Bowden extruders are not attached to the hot end or print head. Instead, the extruder is removed from the print head and is most often attached to the printer body. The filament is then fed to the hot end using a Bowden tube.
Lighter, Faster, and More Accurate
Like the Direct extruder, many of the advantages and disadvantages come from the location of the extruder in relation to the print head. The largest advantage is the reduced weight of the print head. Since the extruder is removed from the print head, there is less weight on the print carriage.
Also, because the print head is lighter, a printer using a Bowden extruder can print faster, more accurately, and more precisely. This can result in either higher quality prints or quicker prints, as the print head can move at higher speeds. Additionally, Bowden extruders are more compact and take up less space than Direct extruders.
While Bowden extruders can increase print speed and reduce the print head weight, there are several disadvantages that make them less appealing than Direct extruders. For one, they cannot use as many filaments as effectively as Direct extruders. While they can print flexible filaments, these filaments tend to bind in the Bowden tubing. Additionally, Bowden extruders cannot use abrasive filaments because these filaments will wear away the inside of the Bowden tubing.
Bowden extruders also need a greater retraction distance and a more powerful motor than a Direct extruder. This is because of the increased friction on the filament in the Bowden tube, which can lead to a less responsive extrusion system, more stringing and oozing on the print, and more resistance and drag with the filament.
There are some companies that are trying to solve some of these issues. One example is Capricorn, which makes a Bowden tube that is supposedly better at printing flexibles and puts less friction on the filament.
Which One Should You Choose?
There are several factors to consider before choosing between a Direct and Bowden extruder. With a Direct extruder, it is important to have a stable printer frame to ensure that the print head can handle the extra weight. With a Bowden extruder, a completely constrained extruder system is important to ensure the filament travels where it should without binding.
It is also important to consider which type of printer you have. A Delta printer needs to have a light print head and must use a Bowden extruder. A Cartesian printer could use either but should have a good frame when used with a Direct extruder. Also, a printer with multiple extruders works best with a Bowden extrusion system.
Finally, the use of flexible or abrasive filaments and the need for quicker printing speeds should also be considered. If you plan on using flexible filaments or abrasive filaments, then a Direct extruder would work best. If you want speed and are using a more standard filament, then a Bowden extruder will work just as well.
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