Direct Drive Bowden Extruder

I wanted an extruder that keeps its tension setting when the filament is released and I wanted it to be easy to use and maintain while looking more finished. To do this, I chose a concept that closes around the drive gear and the tension mechanism. The filament is found completely encapsulated in the extruder and protected from external elements. The beauty of 3D printing is its ability to transform ideas into reality and here is the result:


Bowden extruder direct drive MK8 for 1.75mm filament, open view

Bowden cable extruder direct drive MK8 for 1.75mm filament

Bowden extruder direct drive MK8 for 1.75mm filament

Quick filament change:

Quickly release the filament by sliding the clamp forward. You can then insert a new filament and clamp it back in position. Because of the quick release system, the pressure on the filament is not modified by filament change and you can restart your print directly.

Some filament material are softer than others, some require more pressure to extrude, others tend to grind easily. The tension on the idler can be finely adjusted with two screws for a better grip according to the filament material strength.

It is sometimes necessary to relieve the filament in order to do maintenance. For any reasons, if there is a filament jam anywhere on the line (the hot end for instance), the gear can chip the filament and fill itself with plastic until its grip loosens (mouse bite). It is therefore easy to open and access the gear for cleaning.



Clean looking while protecting the filament:

The drive gear in fact is reliable enough to stop worrying about its operation and start worrying about its usability and its appearance. Its closed form, based on the dimensions of the motor makes it compact and discreet. The gears, springs and nuts are hidden and the relief mechanism stays together.

By sealing off the mechanism, there is a smaller chance that dust or debris will contaminate the filament extrusion. With guide tubes in and out of the extruder, the filament can be protected from the spool to the hot end.


Reliable Drive Gear:

The MK8 drive gear has a good grip on the filament to push it efficiently. It has an effective diameter (7 mm) close to the motor shaft (5 mm) which creates the best torque.

pushing force = motor torque / (effective diameter * pi)

We use this bowden extruder since September 2013 and it is still in perfect condition. Warning: rough surface filament like bronzefill or stonefill can cause premature wear. However that warning is valid for any parts involved with these composite filaments (hotend, nozzle, extruder and so on).

For more information on drive gears and suppliers:

Direct Drive:

The direct drive offers several advantages over gears reduction. Unlike gear systems, there is no backlash that could affect accuracy and fewer moving parts that could break.

The NEMA 17 stepper motor in direct drive configuration is more than enough capable of pushing the filament to a well performing hotend. But in the event of a clogged hotend, it may be better to have a stepper that will loose steps instead of a too powerful motor that will push the filament no mater what, leading other parts to endure the strain or break.



The stepper motors typically used by RepRaps (NEMA 17) generally have 200 steps per revolution and are used with 16 microstepping controllers. This gives us 3200 microsteps per turn. With an effective diameter of 7 mm (MK8) it gives a feed of 0.0069 mm per step (or 0.00027 inch/step), which is accurate enough for this kind of use. For the same drive system, the smaller the diameter of the filament the more accurate it will be. In this case I recommend to use a 1.75 mm diameter filament, which is 2.9 times more precise in respect to volume per step comparison, and it is also widely available.



On both sides there are places to screw a tube connector (look for “Pneumatic Tube 4 mm Push In Fitting M5″).

It can be used in both directions giving you an option to place the hinge up or down. You can also connect two guiding tubes on each side and protect the filament entirely from the spool to the hot end.

The PTFE (teflon) tube offers less friction and is recommended to guide the filament to the hot end.



Brackets are placed on each side in order to ease the assembly on the 3D printer. The holes are spaced 68 mm and have a diameter of 6.5 mm to fit M6 or 1/4 ” screws.

Multiple installation

Multiple material:

Its compact design makes it possible to install multiple extruders side by side or in opposition to extrude different colors or different materials at once.



The two versions are pretty similar and share the same mechanism. The main difference reside in the way the second version is fabricated, by inserting springs and nuts in the plastic parts while they are 3D printed. This make the clamps more finished and user friendly. It does not reduce the bill of material but it reduce the part list for the end user, making it easier to assemble.

Details about the Direct Drive Bowden Extruder V1

Details about the Direct Drive Bowden Extruder V2


We are the designer of this extruder. If you need any minor modifications done, like mirror symmetry for dual extrusion, then please contact us prior to purchase.

Part list

2014-04-07 17.16.58

B- 1x Clamp

C- 1x Pivot cylinder

D- 1x Base

E- 1x Bearing shaft

F- 1x Idler

G- 1x Drive Gear(MK7 or MK8)

I- 1x Ball Bearing (skateboard) 5x16x5mm 625ZZ

J- 2x Pneumatic 4mm Tube Push In M5 Fitting

K- 3x Machine Screw M3x30mm

M- 2x Machine Screw M3x50mm

N- 1x Tube PTFE (Teflon) outside dia: 4mm, inside dia: 2mm, length: as needed

O- 1x Stepper Motor NEMA 17 (not shown)

P- Bolt and nuts diameter M6 or 1/4″ as long as necessary to attach the extruder on the printer (not included)



1- Insert the M3x50 screws (M) in the clamp (B). The screw head should fit inside the bigger holes of the clamp.


2- Insert the pivot cylinder (C) in the main body (D)


3- Screw the M3x50 screws (K) with the clamp (B) and the pivot cylinder (C) through the grooves of the main body (D)


4- Screw fittings (J) on the main body (D).


5- Insert the metal rod (E) in the bearing (I) and insert it in the idler (F), squeeze a bit if necessary.


6- Place the drive gear (G) on the motor shaft (O), taking care to orient the set screw on the flat side. Lightly tighten the screw with an Allen key to hold the gear in position facing up.


7- Use three M3x30 screws (L) to screw the base (D) on the stepper motor (O) without forgetting to put the idler (F).


8- Open the extruder and insert a filament to align the drive gear (G) on it. Fix the gear in position with the set screw (Allen key required).


9- Install the extruder on the 3D printer by using the brackets and M6 or 1/4″ bolts.

10- Insert PTFE guiding tubes in the fitting(s) to the hot end and/or the spool.

Extruder side


Before trying the extruder for the first time, the firmware should be configured properly. If you don’t know how to do this, please read

The calculated feed rate of the extruder should be written in the firmware. For example a 200 stepper motor with 16 microsteps per steps, MK8 (7 mm eff dia), should give something like: 20016/(73.1416)=145.5 steps/mm

  1. Insert the filament in the extruder
  2. Ensure the hot end operates properly and the filament is not overly restrained.
  3. Close the idler with the clamp (spring box)
  4. Tighten the idler by screwing the tensor screws 2 to 3 mm deep.
  5. Start the 3D printer to test the extruder with the free area under the nozzle.
  6. Heat and send the command to extrude a few centimeters. If the filament is not moving but the motor is turning, tighten the screws until it moves. If instead the stepper is not turning or skips steps, you can release some pressure. If you do not get satisfactory results, please inspect the hot end or check for something restraining the filament.

For more details on the calibration of the extruder you can visit this page: