Nextruder filament sensor (CORE One, CORE One L, MK4/S, MK3…

The filament sensor equipped on our Nextruder printers detects the presence of a filament and filament run-out. The sensor is a Hall sensor, triggered by a mechanism composed of a spring, a magnet, and a ball.

On printers upgraded to the Original Prusa MMU3, some of the Nextruder components are modified, including the mechanism that triggers the filament sensor. In these printer versions, the mechanism does not rely on a system of spring, magnet, and ball, but is based on the idler tension bolt.

Check assembly (MK4/S, MK3.9/S)

If your printer is an MK4 or MK3.9, you have received a package with magnets for the assembly. On MK4S and MK3.9S, as well as CORE One and XL, this subcomponent comes pre-assembled in the heatsink.

Note that two magnets are sent, but one is meant to be used in the assembly, and the other is a spare. If your filament sensor does not work, check if two magnets have not been added by accident.

Nextruder with MMU3 modification

When the MMU3 is installed on the MK3.9/S or MK4/S, the Prusa-ball-holder is replaced by a swivel assembly. If you have the MMU modification in your extruder, the steps below still apply, but are applied to the swivel assembly whenever the Prusa-ball-holder is mentioned.

How to clean the filament sensor

During usage, filament residue might build up around the sensor or its mechanism, possibly causing false readings and thus malfunctioning.

1) Compressed air

At the top of the extruder is a small hole, insert the tip of a compressed air can in the hole. With your free hand, prepare a bit of filament with a non-stringy tip. Repeatedly insert and remove the filament from the extruder, while blowing the compressed air. This will dislodge the build-up debris.

Top view of the CORE One (left) and MK4 (right) print head. The XL print head has a similarly positioned small hole.

2) Filament tip insertion

In case you don't have compressed air at hand, a similar procedure to the one above can be attempted.

Prepare a bit of filament with a non-stringy tip. Repeatedly insert and remove the filament from the extruder. It will be necessary to insert and remove the bit of filament several times to achieve good cleaning, and the technique might not always be effective.

3) Removing the sensor

If the previous techniques do not work, the filament sensor can be removed to be manually cleaned. This procedure requires partial disassembly of the Nextruder.

On XL, make sure the firmware version is 6.4.0 or higher, to have access to the needed gearbox alignment procedure from the printer menu. The CORE One, MK4/S, and MK3.9/S have this procedure accessible on all firmware versions.

Ensure to have the PG-assembly-adapter before continuing with the following procedure. If you do not have it, you can purchase it from our e-shop, or you can print it using the files below, depending on the printer you will use.
PG-assembly-adapter e-shop page
PG-assembly-adapter printed with CORE One, MK4/S, MK3.9/S, XL
PG-assembly-adapter printed with MK3/S/+, MK3.5/S

Unload the filament, then wait for the printer to fully cool down. After that, turn the printer off.
Remove the PG-case, together with the PG-ring, gearbox, and main plate. Remove all of these parts in one piece.

Remove the Prusa-ball-holder using pliers.

Carefully remove the ball-magnet-spring combo from the Prusa-ball-holder and clean any debris out of it. Clean also the slot on the heatsink.

Reassemble the Prusa-ball-holder in the following order: steel ball, magnet, and spring. Then, insert the assembled Prusa-ball-holder in the Nextruder.

Reassemble the block with PG-case, PG-ring, gearbox, and main plate.

In case the disassembled parts in step 6 are not in one block, refer to the Nextruder chapter of the assembly guide of your printer model.

Perform the gearbox alignment, following the procedure from the dedicated gearbox alignment article.

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23 comments

Mateusz Popek

•

The instructions on removing the PG case skips one screw that you need to remove. It is located in the lower right corner under the cover plate. You need to have it removed, as it also holds the assembly. All in all you have to remove four screws, three from the cover and one beneath.

Sherweld

•

When attemting filament load .... starts to heat nozzle, after approx 5-10 seconds, faults to "timed out."
Not sure if same behavior with MMU3 unit. Now impossible to load or print with conventional side load via Y splitter. Has worked well previously.

On a hunch, I did a recalibrate (test #10) problem went away. Somehow that sensor setting had become corrupted but seemed a key to everything else.

Dawn Cowe

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I've used the PG-assembly adapter today. Confusing but finally got it to work. Its only needed when. you need to reinstall the gears and to get the ring case which has teeth aligned. Had to watch a few video's to get it right

barriearcher

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It looks from the photograph as if clearing the debris should be done with a length of filament. If this is so it should be more explicit, especially if other methods might cause damage. It would also be a good idea to locate a copy of the assembly guide before starting the cleaning - particularly as the problem of the broken link for the guide has been "solved" by removing the hyperlink!

Andy Smithers

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Have been using my self-build Mk4s most days for about 8 weeks. Filament detector error appeared and blowing through with compressed air did not fix it. However following these instructions, taking off the gear box and taking the Filament detector out to clean solved the issue. Thank you Prusa.

Nextruder filament sensor

(CORE One, CORE One L, MK4/S, MK3.9/S, XL)