Prusa I3 MK3 - New filament sensor adapter in a separate housing.
Get rid of false-positiv alarms from the filament sensor!
09/06/19 News: There is a new variant for use with the Bondtech extruder https://www.thingiverse.com/thing:3681220
02/16/19 News: There is an upgrade for the MK3S-R4 extruder here:
10/02/18 Great News! V2 Upgrade with adjustable spring force!
With an additional M3x16mm screw on the left bottom side, it is now possible to fine tune the spring force for the ball bearing! This extension is especially useful for MMU owners.
Applies only to Part Top (A) and Part Bottom (B).
Recurring false alarms from the filament sensor of my Prusa I3 MK3 have urged me to look for a solution, Firmware 3.3.1, 3.4.0, now 3.4.1-RC1.
The cause of the false alarms are insufficient light reflections from the filament used.
Particularly shiny or transparent filaments provoke a too weak recognition with the optical motion sensor.
In order to avoid this circumstance, the filament movement is transmitted to the sensor via a small ball bearing in my solution.
The sensor thus sees only the movement of the ball bearing, the texture of the filament has become no matter.
The adapter is exchanged with the existing filament cover on the extruder.
To remodel, the existing built-in MK3 filament sensor is removed and used in this new housing.
In addition, a ball bearing type MR63 (6x3x2.5mm, eg at Amazon), some PTFE tube and 2 screws M3x10mm are needed.
The previous connection cable of the sensor is used further and connected to the now 180 ° rotated sensor placed in the new housing.
The ball bearing is pushed onto the spring / axle fitting and inserted into the upper part of the housing.
With the flat side of the spring / axis facing to you, it snaps with some pressure in the top of the case.
The filament sensor is attached to the bottom part of the housing with the existing M3x10mm screw.
2 additional screws M3x10mm connect the two halves of the housing.
The upper part of the housing is available in 3 variants: With a thread to accommodate
some cm PTFE tubing and matching cover (regular 8.4mm outside dimension),
or with a Bowden (push-fit with 6mm thread or PRUSA style brass inlet) connection for eg an MMU extension.
The through hole for the PTFE tubing can be smoothed with a 4.0mm drill to make the tubing easier to place.
The PTFE tube should be lowered slightly at the ends, so that the filament slides in better.
It may be useful to roughen the surface on the outer radius of the ball bearing with, for example, sandpaper (600 ...) before installing it, depending on the type of bearing. This results in a better reflection for the sensor.
It is not necessary to make any changes to the firmware of the printer, I use currently V. 3.4.1-RC1 (German).
The adapter consists of the following components:
Housing top part in 3 variants,
Housing lower part,
Lid for the threaded inlet,
1 x spring / axle 32mm x 3mm.
1 x ball bearing MR63
a few cm of PTFE tube 4 / 2.5mm
5 x screw M3 x 10mm (3 x existing)
1 x screw M3 x 16mm, to adjust the spring force, don't use longer screws!
1 x Original Prusa Filament Sensor PCB (1 x existing)
I print the components with PETG (http://www.dasfilament.de), 0.15mm layer height, 3 perimeter and 20% infill (Honeycomb).
Except for the upper part (eg fs-body_top_V2_A.stl), no supports are needed.
The top part has a few small overhangs and bridges, for me it worked without supports.
The printing should also work with PLA or ABS, but not testet yet.
Comments, questions and suggestions are always welcome.
I wish you happy printing