3D Printing / Import Extruder

Assembly of my all metal version of the Mk8 import extruder

Click on the images for more detail.

Start by screwing the base plate to the stepper with the M3x6 screw.

Add the M3x8 screw to the bottom of the base plate. This screw helps to retain the tension spring later on.

On the Tension arm add the bearing and broad headed screw. If the bearing does not spin freely, flip it over. One side is slightly offset.

Partially insert the M4x20 screw into the tension arm. This screw will later control the pinch tension on the filament.

Use the M3x15 screw to attach the arm to the base plate and stepper. use light tension to ensure the arm freely pivots.

Add the drive gear to the stepper shaft. Make sure to align the first set screw to the shaft flat.

The drive gear should be centered with the tension bearing. Snug down both set screws.

Use the M5x5 screw in the top of the spring. Wedge this stack between the lever arm and base. The screw at the top should now control filament pinch tension.

The insulation has be taken off to illustrate the importance of this step. The nozzle and throat tighten against each other, the should be a small gap between the nozzle and the heater block. This means a leak free seal between the two. Do not tighten the nozzle to the block. The nozzle needs to be tight and double checked on first heat but this small gap must remain or it will leak.

How the nozzle looks as assembled with the insulation, and the nut to position the nozzle. Make sure not to get any insulation in the nozzle and clog it.

Thread the nozzle assembly into the base as far as possible, snug the nut carefully. It does not need to be tight just snug.

Add the heater cartridge and guide the thermistor into the small hole. Ensure it is fully inserted. Gently snug the heater cartridge set screw, careful not to damage the heater. make sure not to move the fragile wires excessively and ensure they are not twisted and sorting out.

Line up the heatsink.

Add the fan sticker facing the heatsink, fan guard, and snug it up with the long screws.

Secure the wires to the top fan hole, and your done with assembly.

Plug it in

More detail here.

You will need power to both sides of the green plug, you can just add a short jumper wire from one side to the other. The polarity is marked on the board, double check to make sure this is correct. The fan on the heat sink needs to always run, this gets plugged directly into the green power plug, polarity matters. Extruder to port D8, polarity does not matter. Optional print fan plugs in to port D9 polarity matters.

Marlin edits

Very few edits required. Any firmware I release after this post will most likely already be set for this extruder by default. I will put the info here for you adventurous types.

Pre-set Firmware

All of these that I have gotten have used the marlin #11 thermistor, and at 32nd stepping I use 200 steps for the e value.

#define TEMP_SENSOR_0 11

and

#define DEFAULT_AXIS_STEPS_PER_UNIT {200,200,4535.44,200}

Even after running the PID auto tune I get a huge overshoot in temp so limiting the max current might help with this, I will update it when I get a chance to test it.

// Comment the following line to disable PID and enable bang-bang. #define PIDTEMP #define BANG_MAX 255 // limits current to nozzle while in bang-bang mode; 255=full current #define PID_MAX BANG_MAX // limits current to nozzle while PID is active (see PID_FUNCTIONAL_RANGE below); 255=full current #ifdef PIDTEMP

Slicer edits

Delete the beginning gcode, you don’t want it to home.

Change the end gcode to look like this

G91
G1 E-5 ;retract
G1 Z5 ;lift up 5mm
G90
M104 S0 ; turn off temperature
M84 ; disable motors

Not using endstops

Position you parts on the lower corner (0,0,0), before you slice them. This will start your prints where ever your head is. So position the nozzle touching the bed and exactly where you want it to start. When the print begins it should lift up the correct amount and print. You can manually adjust the height during the skirt print to fine tune it.

That’s it print away. The printed parts I am shipping are starting to get printed on this cnc, and they look amazing.