READ THIS TO BETTER UNDERSTAND THIS MOD BEFORE PRINTING
This mod needs you to flip the IR sensor connector so be ready to swap cables as described below. You can damage the sensor if you will not follow these instructions.
Updates at the bottom of the page: last updated on January 2, 2023.
IFS
This modification integrated the external filament sensor inside the original extruder body of the Prusa MINI. It already exists a similar mod for the Bondtech version but I wanted it in the original one, hoping to give inspiration to the Prusa Team.
This is not a perfect conversion because of the tight spaces I had to work with but after you set it up it works flawlessly.
I didn't want to make the whole extruder block larger so I used the solid areas left inside the original parts to accommodate the sensor and a lever working, as usual, with magnets and the steel ball.
Warning: many users reported a noticeable increase in the extruder noise and gear rubbing against each other. This does not affect in any way the correct functioning of the extruder. If you are ok with this eventuality proceed.
After investigations and thanks to your comments seem like the cause of this problem is not geometry related. The same components printed on the Prusa MK3s (instead of the MINI) worked perfectly without any noise problems. The Prusa MINI needs to be well calibrated before printing these parts or they will not be good enough: this printer suffers especially from XY and XZ skew so take care of it.
If possible, to avoid any problem, it is preferable to print these parts on a well-calibrated printer, like Prusa MK3s or other standard cartesian printers.
PARTS NEEDED
No screws are needed than the printer's ones but you'll need the full filament sensor kit for the MINI or the MK3S.
PRINTING
The gcode is available and will print the four components needed sequentially:
MINI-extruder-front-IFS
MINI-extruder-rear-IFS
MINI-extruder-lever-IFS
MINI-extruder-idler-IFS
There is an alternative version of the extruder-rear part with the M10 thread coupler if you need it; just don't print it if you have the standard coupler.
Use PETG filament (or tougher), 0.2mm layers, at least 3 walls and 15% gyroid infill. IMPORTANT: be sure to use the Arachne Perimeter Generator if the slicer allows. Otherwise, set 0.38mm external perimeters width or some perimeters will not be printed correctly.
NO SUPPORTS IS NEEDED!
The lever is the most critical part and it should be printed slowly with 4 walls, in order to not melt the top part that will interact with the filament sensor. It has to be printed in a dark matte filament (possibly black): the IR sensor must be triggered by the lever.
The rear part has one layer that covers the channel to adjust the motor screw that needs to be removed (purple area in the image below). You can use the pliers.
This mod needs you to flip the connector so I hope you are ready to SWAP THE LATERAL CABLES or you could break your filament sensor. This can be done using a small screwdriver or a tweezer pushing on the metallic area of the cables inside the connector. Here you can see how the connector has to be placed.
The connector shown is not exactly the PRUSA's one because of its “wings” but don't worry, the component's design fits perfectly with the original one.
ASSEMBLY INSTRUCTIONS
Part 1: DISASSEMBLY
Remove the original extruder body and remove everything, motor, screws, bearings, gears (not from the motor), PTFE tubing and couplers, except for the idler lever if you want to use the original one
Do the same with the external filament sensor
Part 2: FRONT
Place the bearings and the nuts in the new parts the same they were in the original ones (some of them will not be used)
Place the filament sensor facing up in the MINI-extruder-front-IFS and lock it with its screw: do not overtighten it or you could break the sensor; SWAP the RED and BLACK cables of one end of the connector; connect its cable now or at the end of the assembly as shown in the images (check again for the correct order of the cables and the direction of the connector)
Attach the motor as in the original parts; note that there is an enlarged hole for one of the two screws in order to adjust the pressure of the motor against the extruder gear: make it as close as possible or it could introduce backlash in the movement of the gears. If you make it a bit looser it should solve the previous noise issue but could lead to a different noise, so try adjusting it until is optimal for you. ADJUST WILL BE COMPLETED AT THE END OF THE ASSEMBLY (see part 6).
Insert the extruder gear in the bearing matching the gear on the motor (the gear on the motor should be already on it)
Part 3: REAR
Insert the first magnet in the MINI-extruder-lever-IFS; the friction should increase toward the end of the hole, keeping it in place. If the friction is not enough try applying a little stripe of tape on the magnet to increase its thickness
Put the steel ball in the MINI-extruder-rear-IFS: it will go into a little pocket inside of the lever insert section of the rear housing (→)
Place the lever inside the MINI-extruder-rear-IFS, making sure the steel ball stays in place inside the cavity
Fix it with an M3x12mm screw
Place the second magnet in the MINI-extruder-rear-IFS with the opposite polarity of the lever, in order to repel each other
Slide the M3x25mm screw that will lock it in place
Unscrew the M3x12mm screw of the lever just enough to make the lever free to move
Part 4: SANDWICH
Align the two main assemblies built in Parts 2 and 3, taking extreme care of the alignment of the bearing and the filament sensor lever
Insert the square nut, bearing and metal pin inside the Idler lever (MINI-extruder-idler-IFS); make sure the bearing can spin freely; place the idler inside the body
Use the three M3x25mm screws to fix it (remember to tighten also the screw on the magnet placed in Part 3.6; do not overtighten it or you could break the magnet)
Use the M3x40mm screws with his spring to tension the Idler
Insert the PTFE tube in the lateral hole; it can be the size you want: I used a really short piece with a 3mm bore diameter for ease of use. At the moment there is no designed feature in order to keep it firmly in place (because of its short length) but a piece of tape or a drop of glue should do the job if it falls out
Part 5: MARRIAGE
Place the whole extruder assembly on the printer and fix it with the M3x25mm screws (remember to place the inspector door in place)
Slide the extruder motor and filament sensor cables inside the main nylon sleeve
Connect the extruder motor and filament sensor cables in place
Close the mainboard box
Part 6: MOTOR TENSION
In this stage, you can better adjust the tension of the gears, releasing the motor screw, twisting it in the desired position and fixing it in place. There are holes in the rear part of the extruder body to pass through with the Allen key, reaching the screw on the front part that retains the motor.
You can adjust this every time you need, just remove the whole extruder body from the printer and unscrew the Idler tension screw to lift it up: now you can access the two screws of the motor.
It is possible to feel the correct tension moving back and forward the larger extruder gear with a finger: if you can hear a delicate “tik” sound it means the gears are too loose; if you are not able to do at least a full turn without too much effort they are too close. When the gears are too close they can jam or cause unwanted noises.
COMPLETED
Enjoy the IFS ease of use, everything else is the same. Hope my work can be helpful or at least be a suggestion for something similar.
All the parts have been printed and tested. If you have any suggestions or if something doesn't work as expected feel free to write a comment. Read the other comments to answer frequent questions.
Edit January 2, 2023: updated description for better readability and clearer warnings. No changes to the models.
Edit July 18, 2022: updated description. No changes to the models. Maybe the noise problem is solved (read the description).
Edit May 17, 2022: added the MINI-extruder-rear-IFS_M10 version, with the PC4-M10 thread.
Edit March 28, 2022: added holes in the rear part of the extruder body for easy access to the motor screw. It was challenging to adjust the motor tension on the gears with the extruder body not completely assembled so now it is possible to fix them with all the components in place. Updated 3mf files of MINI-extruder-front-IFS and MINI-extruder-rear-IFS. Updated gcode.
Edit March 19, 2022: big update: hope to have solved all the issues, particularly the annoying problem of the extruder noise, by introducing an adjustable placement of the extruder motor against the extruder gears. Added a maybe useless cleaning channel to avoid excess debris accumulation inside the gears chamber. Modified filament sensor cable path to avoid being pinched with the idler lever. Last, I decided to simplify everything leaving only the essential and working components for the original version of the Prusa MINI. If you want older or alternative versions let me know. Here you can see some of the features I added.
Edit January 26, 2022: minor update for the assembly instructions: some passages were not clear enough.
Edit January 19, 2022: minor changes to the geometry of the front component, in order to avoid the locking of the filament sensor cable inside the body.
Edit January 18, 2022: minor description and assembly instructions changes.
Edit January 16, 2022: modified every component in order to fit the original connector of the filament sensor and added some features that will retain the magnets. Added range of movement for the filament sensor lever. Revisioned assembly instructions and updated the gcode with the new parts. Removed STL files: now only the 3MF files are available (tell me if you really need STL files).
In the older version, there was not enough space for the lever and now there is.
Edit January 13, 2022: modified the MINI-extruder-rear-IFS part for the M8 thread because of some incorrect dimensions and added the M10 version. Comment if you need different types of threads.
