Prusa MINI+ direct extruder mod with original motor and printhead

Story

I gradually started to hate bowden extruder, as it required neverending tweaking of PETG print settings, giving either gaps&blobs or stringing. I tried to find solution, with using as many hardware stock parts as possible. It all began with dual-Z axis CK3D mod with modifications, which really improves print quality even with bowden, but direct extruder was logically the target solution. I found only one direct drive mod here, but it was created for single-Z and heavily limited print height with dual-Z to approximately 120 mm. Therefore I created my own mod based on original extruder parts for MINI+, modified them and created supporting parts for mounting. In total, there is 4 main parts, 1 cable clip (2×) and 1 PTFE tube clip. I also used extruder placeholder for cable and PTFE management.

Whole mod should not limit print area with CK3D at all as I did check clearances (see photos). However cable routing on the back of extruder is very tight to the left side, so think about it while printing in z-axis extremes (>Z170 with <X10).

Update 2024-09-05: I created front clip for PTFE as it in original position might get squeezed to top extrusion while printing at high Z.

Print instructions

PETG, 0.2 mm layer, 0.4 mm nozzle, 15% infill (100% for clip), 3 perimeters, no supports.

There might be catch with slot in MINI-extruder-rear-sAd, you can use custom supports, but slot is probably not needed anyway, so it is your call.

Hardware parts

Sorry, I didn't track down all used M3 hardware dimensions as I had been changing them all the time. But you will need assortment of M3 screws from 12 mm to 40 mm, some standard and square M3 nuts. You might also need 4/2 mm PTFE tubing, if you want to use original side loading of filament.

Mounting

1. Assemble front and rear extruder part similarly to original MINI guide. This includes motor, gears, etc.
2. Mount MINI-extruder-holder-right-sAd to extruder as it will be impossible to insert screw, when it is mounted to x-carriage.
3. Mount idler into extruder
4. Mount MINI-extruder-holder-left-sAd to printhead (it can be left on x-carriage), inluding heatsink fan, MINDA holder
5. Put extruder assembly onto printhead fitting without nut (see photo). It should fit without any problems. Do not forget to insert short PTFE from original extruder. Mount it to printhead on right side.
6. Mount cable clips as shown in photos. You can also be inspired with cable management.

Firmware modification

You should modify firmware for loading and unloading of filament, as it is hardcoded. However, you will loose your warranty.

Download latest firmware source code and look into \include\marlin folder for Configuration_MINI_adv.h . Change given lines as follows:

#define FILAMENT_CHANGE_UNLOAD_LENGTH 400 // (mm) The length of filament for a complete unload.

to

#define FILAMENT_CHANGE_UNLOAD_LENGTH 135 // AS - for direct extruder

and

#define FILAMENT_CHANGE_FAST_LOAD_LENGTH 320 // (mm) Load length of filament, from extruder gear to nozzle.

to

#define FILAMENT_CHANGE_FAST_LOAD_LENGTH 52 // AS - for direct extruder

Compile, upload and enjoy.

Reworked MINI-extruder-front and MINI-extruder-rear for better fit.