Have you ever wished that you knew exactly how much filament was left on the spool so that you could plan out big 3D prints and spool-changes better? I set out to solve that by attaching a small mechanism on the 3D printer that would keep track of filament used.

This is a proof of concept for a purely mechanical design. Filament is pulled through the device by the extruder, the filament spins a wheel, which in turn drives a set of gears that count upwards. The wheel and gears are sized to count out the length of filament passing through in centimeters. A typical 1kg of 1.75mm filament is 330m for PLA and 400m for ABS.

My discoveries were:

• 3D printed gears are pretty good, the printed parts have low friction, meaning that gears rotate freely, and even a 3D printed axle is low-friction enough for non-load-bearing gears.
• Unfortunately, because of the low friction, the filament would slip past the wheel without spinning it. Some other material, like an elastic band, has to be added to generate enough friction between the wheel and filament for it to work.
• A lot of careful design is needed to prevent jamming the geneva mechanisms, more rounded edges are needed basically everywhere two non-coplanar gears meet.
• Part of the cause for jamming is size tolerances - every printer and even slicer setting will cause slightly different print sizes, and also printing artefacts, that affect the performance of the mechanism.

This isn't the finished design for a filament travel counter, it is a proof of concept only. It only counts on 4 digits, meaning it'll only count up to 99.99m of filament before rolling over, and is sized for 1.75mm filament (one extra dial needs to be added to work with 1kg spools, this can be easily done). And there is no mounting system to attach it to a 3D printer.

I've decided not to continue with working on an all-mechanical filament counter. While this counter work in principle, so much effort will be involved in fine-tuning the design, that actually it would just be easier to use a 3D print manager that keeps track of filament usage in software. (Though the benefit of an all-mechanical counter is that you can print a separate counter for each spool that you have, giving you the freedom to switch spools without having to mess with your filament counter).

Video of action: https://www.youtube.com/watch?v=w5Znb5UNO8I