Simple Filament Sensor

youmagine

I decided to create a sensor that detects large spots in filament after experiencing two failed prints in one roll due to those pesky spots. It turns out that an ink tube from a BIC pen has the perfect ID for 1.75mm filament, which is exactly what I needed. After printing the two parts, press a small piece of the ink tube into the arm, and this will become the 'calibrated' size - the filament should slide smoothly through it. Assemble everything as shown in the picture; you might be able to use this without the spring, but I wanted to make sure that the print wouldn't pause accidentally, so I made the arm spring-loaded. When the extruder pulls the filament and encounters a large spot that could cause a clog, it will get stuck in the ink tube inside the arm, causing the arm to activate the switch and pause the print. During assembly, you'll need to drill out the holes for the filament to ensure they don't have any restrictions; even large spots should pass through the holes in the printed base, so make sure they're large enough for some variability. If you don't have screws small enough to mount the switch, it's okay to glue it in place with super glue - just ensure that the holes line up as if screws were installed. I used 2mm brass rod to hold the spring in place, but a nail or other wire should work just fine; I made the holes super small, so they'll need to be drilled out to whatever size of wire you want to use. I had two small springs installed when I took the picture, but it's designed for a pen spring. The printed arm does require some support material during print, and after printing, remove the dense support material with a small saw - it works quite well.