Prusa Mini Direct Hextruder Retro

Update V1.1 (10/22/2021)

• STEP file for v1.1
• Extruder v1.1: some fix and more sturdy

I really like the extruder of @Vez3D youtube channel and looking for it for a while. Finally @MAMSIH release his Hextruder which really impressive. I love his design but for me it have some problem:

• I don't have any heat insert
• I don't have plastic PTFE coupler
• His PINDA sensor holder integrated with X Carriage is weak and fragile
• Air flow of cooling part fan is not exactly match with Vez3D design

Therefore my design address this problems by:

• Replace heat insert required part to using nuts
• Use M6 PTFE coupler
• Seperated PINDA holder with hotend fan cover
• Recreate XCarriage Fan airflow to match the design of Vez3D

BOM

See @MAMSIH page for more detail

Printing instruction

Print parameters

• Material: ABS (recommended), PETG
• Number perimeters: 4
• Layer height: 0.2
• Support: No need for support except for extruder parts need support on build plate only

Print direction

• Extruder

Note: Print with support on build plate only

• Adapter

• XCarriage

Note: with this direction there are some flaw in the model that it is not flat. You can use split model of prusaslicer and cut 0.5mm.

Printer setting

Extruder setup

Use this GCode in “Start G-Code” in printer setting section:

M92 E705 ; Direct drive extruder steps
M906 T0 E300 ; Extruder current ref

Additional: Linear advance

Beside configure step and motor current, you can callibrate “linear advance” K value (search google for it) for better result. For me, I user K value of “0.08”, insert this GCode in “Start G-Code” in filament setting section:

M900 K0.08

Note: comment 2 default line of prusa.

Additional: Retraction

The default retract distance profile for the Mini is 3.2mm, this is considered to be pretty long for Direct extruder. I set it up to 1mm (or 0.8mm similar to MK3S)

TPU performance

Currently I'm very happy with my setup. I can print 2x faster with better quality and I confident I can print even faster.

About filament changing

It will be a little tricky when you need to load/unload or changing filament. While Prusa Mini use bowden extruder, the load/unload distance is 420mm long (the number is in the firmware) this is not good for direct drive (around 61mm with my setup). So, there are 3 ways to combat with whis:

1. Heat up the nozzle and manual pull/push filament to load/unload filament.
2. Heat up the nozzle and use M701 /M702 to load/unload filament.
3. For advanced user, use can modify the firmware by tuning ADVANCED_PAUSE_FEATURE section, my configurations right now:

#define ADVANCED_PAUSE_FEATURE
#if ENABLED(ADVANCED_PAUSE_FEATURE)
    #define FILAMENT_UNLOAD_RAMMING_SEQUENCE \
        { \
            { 1, 100 }, \
            { 1, 300 }, \
            { 3, 800 }, \
            { 2, 1200 }, \
            { 2, 2200 }, \
            { 2, 2600 }, \
            { -2, 2200 }, \
            { -20, 3000 }, \
            { -30, 4000 }, \
        }
    #define PAUSE_PARK_RETRACT_FEEDRATE 20 // (mm/s) Initial retract feedrate.
    #define PAUSE_PARK_RETRACT_LENGTH 2 // (mm) Initial retract.
// This short retract is done immediately, before parking the nozzle.
    #define FILAMENT_CHANGE_UNLOAD_FEEDRATE 10 // (mm/s) Unload filament feedrate. This can be pretty fast.
    #define FILAMENT_CHANGE_UNLOAD_ACCEL 625 // (mm/s^2) Lower acceleration may allow a faster feedrate.
    #define FILAMENT_CHANGE_UNLOAD_LENGTH 80 // (mm) The length of filament for a complete unload.
//   For Bowden, the full length of the tube and nozzle.
//   For direct drive, the full length of the nozzle.
//   Set to 0 for manual unloading.
    #define FILAMENT_CHANGE_SLOW_LOAD_FEEDRATE 10 // (mm/s) Slow move when starting load.
    #define FILAMENT_CHANGE_SLOW_LOAD_LENGTH 30 // (mm) Slow length, to allow time to insert material.
// 0 to disable start loading and skip to fast load only
    #define FILAMENT_CHANGE_FAST_LOAD_FEEDRATE 10 // (mm/s) Load filament feedrate. This can be pretty fast.
    #define FILAMENT_CHANGE_FAST_LOAD_ACCEL 625 // (mm/s^2) Lower acceleration may allow a faster feedrate.
    #define FILAMENT_CHANGE_FAST_LOAD_LENGTH 20 // (mm) Load length of filament, from extruder gear to nozzle.
//   For Bowden, the full length of the tube and nozzle.
//   For direct drive, the full length of the nozzle.
//#define ADVANCED_PAUSE_CONTINUOUS_PURGE       // Purge continuously up to the purge length until interrupted.
    #define ADVANCED_PAUSE_PURGE_FEEDRATE 3 // (mm/s) Extrude feedrate (after loading). Should be slower than load feedrate.
    #define ADVANCED_PAUSE_PURGE_LENGTH 50 // (mm) Length to extrude after loading.
//   Set to 0 for manual extrusion.
//   Filament can be extruded repeatedly from the Filament Change menu
//   until extrusion is consistent, and to purge old filament.
    #define ADVANCED_PAUSE_RESUME_PRIME 0 // (mm) Extra distance to prime nozzle after returning from park.

// Filament Unload does a Retract, Delay, and Purge first:
    #define FILAMENT_UNLOAD_RETRACT_LENGTH 30 // (mm) Unload initial retract length.
    #define FILAMENT_UNLOAD_DELAY 5000 // (ms) Delay for the filament to cool after retract.
    #define FILAMENT_UNLOAD_PURGE_LENGTH 16 // (mm) An unretract is done, then this length is purged.
    #define FILAMENT_UNLOAD_PURGE_FEEDRATE 20 // (mm/s)
    #define FILAMENT_UNLOAD_PHASE1_LENGHT 35 // (mm)fast phase
    #define FILAMENT_UNLOAD_PHASE2_LENGHT 45 // (mm)slow phase

    #define PAUSE_PARK_NOZZLE_TIMEOUT 45 // (seconds) Time limit before the nozzle is turned off for safety.
    #define FILAMENT_CHANGE_ALERT_BEEPS 10 // Number of alert beeps to play when a response is needed.
    #define PAUSE_PARK_NO_STEPPER_TIMEOUT // Enable for XYZ steppers to stay powered on during filament change.

//    #define PARK_HEAD_ON_PAUSE // Park the nozzle during pause and filament change.
//#define HOME_BEFORE_FILAMENT_CHANGE           // Ensure homing has been completed prior to parking for filament change

    #define FILAMENT_LOAD_UNLOAD_GCODES // Add M701/M702 Load/Unload G-codes, plus Load/Unload in the LCD Prepare menu.
//#define FILAMENT_UNLOAD_ALL_EXTRUDERS         // Allow M702 to unload all extruders above a minimum target temp (as set by M302)
#endif