Dual Gear Drive Extruder for Prusa mini/mini+

This mod is aimed at people who own the prusa mini and nothing else. Therefore all parts, except for the bondtech drivegear set, come from your prusa mini. That means the price for this mod is around 30 $USD. This extruder is meant to be a possible solution to problems with the stock extruder. My stock extruder suffered from under extrusion and skipping as an example.

[Paragraph about flexible filaments has yet to be made]

If you only want the dual gear drive you can download “Extruder without filament sensor.3mf”. Skip the sections “Salvage (Filament Sensor)” and “Assembly (Filament Sensor)”.

BE WARNED

I am not responsible any problems with your printer after installing this mod. Proceed at your own risk.

BOM - "Bill of Materials"

You need to buy the bondtech drivegear set with the type "1.75 / 5.0". All other parts can be salvaged from your old extruder and filament sensor. As said, this costs about 30 $USD.

Printing the Parts

I printed my parts in PLA with the "0.20mm Quality" preset in Prusa Slicer. I advise against going with a larger layer height mostly because of the fitting thread. I also advise against going with the Speed preset. But feel free to choose settings you want, I can't stop you. :)

PETG

For people printing in PETG (bless your soul) turn on “Avoid crossing perimeters” and print every part separately to avoid stringing. The option “Avoid crossing perimeters” can be found in Print Settings > Layers And Perimeters > Quality (Slower Slicing). Here's a before and after picture of the travel moves.

“Avoid crossing perimeters” doesn't work if there are multiple objects. That's why I recommend you to print the parts separately.

Parts

To build this extruder you need:

And for the version without a filament sensor you need this:

(Don't forget to print the model under “Without Filament Sensor” instead of "Housing.stl")

Also

You're going to need either a wire-cutter or a pair of scissors to cut the zip-ties as well as some way to get the magnet out of the old filament sensor. Be that pliers or a hammer, just be careful not to break the magnet. I accidentally chipped mine. If you don't want the filament sensor you can skip this and only get your scissors.

Salvage

Unload filament from the extruder. This will take a few minutes, but please be patient. Don't proceed before unloading.

Unscrew the fitting nut and use your wrench to remove the fitting. Save the fitting for the assembly.

Remove the cable from the extruder by cutting the zip-ties. I'm using cable-ties instead though, since I want to reuse them.

Remove these 2 M3x25 screws while supporting the extruder with your other hand, after these screws are removed the extruder will be free from the assembly. Save the screws for later.

Remove the long M3x40 idler screw and spring.

Remove the M3x25 screws. Then open up the extruder and remove the two M3x12 screws holding the motor in place. Save the M3x12 screws and 2 of the M3x25 screws for the assembly.

Use your 1.5 mm allen key to unscrew the drive gear from the motor shaft. Disconnect the motor from the buddy board.

Push out one of the hex nuts with your Allen key and you're done!

Salvage (Filament Sensor)

For the filament sensor you need the steel ball, the magnets, the IR sesnor and cable, a M3x12 screw as well as the M2x8 screw. Everything can be found in the stock Prusa Mini+ filament sensor.

Credit to Prusa for the images.

Remove the PTFE tube from the filament sensor by unscrewing this screw (green arrow).

Remove two M3x12 screws (green) and open the filament sensor.

Remove the lever by unscrewing it's M3x12 screw (Red). Take the ball and the magnet from the lever. Save one of the M3x12 screws as well.

Remove the IR sensor by unscrewing this M2x8 screw with your 1.5mm Allen key.

This magnet can be hard to remove. I used a wire cutter to remove it. Please be careful though, I accidentally chipped my magnet by doing this.

Don't forget to disconnect the filament sensor from the Buddy Board.

Assembly (Filament Sensor)

Please note that many parts of the design have changed since I took these pictures.

IR sensor

Put the IR sensor into place and plug in the cable. Tighten it down with your 1.5 mm Allen key and the M2 x 8 screw.

Lever magnet

Push the magnet into the lever. It will take some force. but be careful! Do not break the thin part!

Leave about 2 mm clearance so that the magnet does not stick out the bottom

Housing magnet

Place the other magnet so that the lever is attracted to it. I drew a line to help you keep track of the right orientation.

Ball and Lever screw

Drop the ball into place and use a M3x12 screw to fasten the lever. Don't over tighten, the lever should be free to move.

Assembly (Extruder)

Fitting

Start by tightening by hand to make sure the fitting is aligned. Then use your wrench to finish the job.

Idle gear

Put the idler gear shaft into it's hole. Drop on the bearings and gear.

Drive gear

Screw the drive gear onto the motor with your 1.5 mm Allen key. Aim for 3 mm from the end of the shaft to the drive gear. Check for alignment with the idler gear and redo if you're not satisfied.

Door

Attach the door to the assembly with a M3x25 screw. It should be able to move freely.

Spring loaded door

Use the screw pulling technique to get the M3n nut into it's hole. Then screw on the spring loaded M3x40 screw on the front of the door.

The last screws

Screw the last M3x25 screw into place and mount the extruder to your Mini with the M3x12 screws.

Cables and Fitting nut

Lastly screw on the fitting nut and use your cable-ties or zip-ties to tie down the cable. Don't forget to plug the Motor and Filament sensor into the Buddy Board.

Firmware (IMPORTANT)

Start your printer, go into Settings and long press on the tab Hardware. After about a second it makes a sound and opens a new menu. Here you can change the extruder step length to 140.

Heads up: For older firmware versions the procedure might be different.

Congrats!

Give yourself a pat on the back, you did it! Award yourself a snack. (Preferably gummy bears)

If anything went wrong, was unclear or didn't work then please leave a comment. I'll do my best to respond. I'm glad to help.

Use the STEP file to edit the model to fit your needs. If you're new to CAD but still want to edit the model, I recommend Onshape. As a bonus I will include the link to my Onshape document here. Happy cading!

Everything except for the drive gear set can be salvaged from your prusa mini.

Half as many parts.

Fits the Prusa mini parts instead of the mk3s parts. (Fitting and magnet)

I removed the chain connector.

This extruder is smaller.

The Spring screw is moved to the front for easy access.