Low Profile Filament Runout Sensor

thingiverse

All mechanical runout sensor designs seem to have a major drawback: the microswitch is aligned with the filament path. This design flaw is fine for bowden setups, where the size isn't really an issue, but on direct drive extruders, anything on top of the printer reduces the available print volume. Of course, you can place the sensor away from the extruder, but then you're left with a length of wasted filament. I've also found that many designs can be tricky to load/unload and tend to catch the filament. To eliminate these issues, I designed my own runout sensor using a 5mm ball bearing to actuate a microswitch. This switch is mounted perpendicular to the filament path for smoother operation. A second ball bearing is used as a contact point instead of a 3D printed surface, giving a much smoother ride; the filament slides through easily and doesn't catch even if it's been chewed up by the extruder or melted out of shape. This design also allows for very smooth retraction back through the mechanism when a runout is detected. As a result, you can mount the sensor right on top of the extruder, which was my goal with this design. I've got a balco touch (Wanhao Di3 Plus clone) so I've got a file that fits nicely into the extruder assembly. The microswitch is mounted with M2 screws, which can thread directly into the printed part. I've also uploaded the Fusion 360 source files so you can adjust them to fit other printers or suit whatever size of micro switch or ball bearings you might have lying around.