Step 4 – Flexible shaft

Transfer of drive between motor and extruder must be precise and absolute. Any end to end deviation will have a significant and noticeable impact on print quality.

The main source of this would be from twist in the shaft. This can happen for several reasons.

  • Insufficient gear reduction (shaft overload)
  • Driveshaft spec/diameter to low (inferior grade components)
  • Shaft driven in wrong direction under load (poor design)
  • Incorrect tooth profile (non-involute)
  • Incorrect distance between gear centers

Among the issues this can cause are

  • Wavy print surfaces
  • Inconsistent flow rates
  • Poor retract performance
  • Stringing
  • Blobs and “zits”
  • General poor quality print output
  • Reduced performance lifetime
  • Premature shaft failure.

Flex3drive uses a heavy duty bi-directional 4mm diameter flexible shaft to specifically avoid these issues. Driveshaft construction is four alternately wound, multi-strand windings around a solid central core.

Flex3Drive Driveshaft strip down
Flex3Drive driveshaft wire diagram



Even though the shafts are bi-directional, one direction still has a notable load advantage compared to the other due to how the layered windings interact under load. Flex3Drive uses this to advantage by design.

Flex3Drive Driveshaft function good load


The arrangement of the worm and wheel gear is specifically intended to run the worm gear in counter clock-wise direction as viewed from above. This ensures the driveshaft is running in correct direction during print moves. This results in:

  • Higher torque capacity
  • Clean smooth surfaces
  • Crisp details
  • Sharp well formed corners
  • Bullet proof performance and durability
  • A big step change in your 3d printing output.

So long as the driveshaft is correctly installed, it will provide tens of thousands of printing hours without any performance degredation.

4.1 Fitting shaft coupler and motor cap

A printed coupler attaches the flexible shaft to the motor shaft, and a motor cap to support the nylon outer sleeve. These two items are standard across ALL Flex3Drives.

Flex3Drive motor mounting parts
Flex3Drive motor mounting parts
Flex3Drive Motor Cap and Shaft coupler
Flex3Drive Motor Cap and Shaft coupler


Please take care not to over tighten the M2,5 bolts that are used for clamping onto the motor or flex shaft and for supporting the outer sleeve.

4.2 – Mounting the motor

There are a couple of options shown below for fixing the Nema 17 motor to the frame of various 3D printers. these include brackets for UM2 style machines, CR10 and Prusa Mk2/3.

These mounts can be fitted straight onto aluminium extrusions aswell.

Flex3Drive UM2 Style motor mount bracket
Flex3Drive UM2 Style motor mount bracket
Flex3Drive simple motor mount clamp CR10 style
Flex3Drive simple motor mount clamp CR10 style


As a general rule, it is best to have a nice unstretched loop of flexible shaft when the extruder is at its furthest point from the motor. Equally however we want to keep the driveshaft as short as possible.

For majority (nearly all) delta style printers, it is best to mount the motor approximately half way up the build volume height measured upward from the bed. Do not confuse this with halfway up the overall height of the machine. The flex shaft should loop under the top of the frame.

For Cartesian printers, it is most ideal to mount the motor onto the X axis gantry so it sits on the same plane as the print head but is not always possible.

For XY gantry style printers such as Ultimakers, DBots, HBots. CoreXY, one can mount at a corner or in the middle of the rear upper frame cross-member.

In some instances it can be mounted a little way down on one of the corner uprights. This allows a little more movement reducing forces when the extruder is near the motor mount