Most consumer 3D printers today utilize the fused-filament fabrication (FFF) process, because it offers a great balance between cost, speed, and quality. How well your parts turn out is, of course, highly dependent on your specific 3D printer model and how well it is calibrated. But that isn’t the only factor; filament diameter — the consistency of that diameter in particular — has a tremendous impact on the quality of your 3D-printed parts. Cheap filament with an inconsistent diameter will result in over and under extrusion, which ultimately results in ugly parts with poor dimensional accuracy. To grade filament diameter consistency, Thomas Sanladerer built this 3D filament tester to take detailed measurements.
It’s hard to overstate the importance of consistent filament. Your 3D printer almost certainly operates in an open loop manner, meaning it does not respond to any feedback during the printing process. It just follows the g-code instructions. That means that the printer has no way of knowing if a portion of the filament is thicker or narrower than the rest. You just set the average diameter to calculate the extrusion rate. If part of the filament is thicker, extra material will be extruded. The opposite is also true and both scenarios have a negative impact on quality. Any deviation from perfect cylindricity can also have an effect. For that reason, good filament manufacturers attempt to make their filament as consistent as possible. This will be specified as a tolerance like “+/- 0.03mm” on the package.
The question is how accurate that tolerance information is. To find out, Sanladerer’s machine measures the filament across three separate sets of diameter points. That’s a major benefit over similar machines that only measure across one set of points, which doesn’t account for cylindricity issues (when the filament cross section is an oval instead of a perfect circle). The machine is controlled by an Arduino Uno that drives stepper motors to spool and unspool the filament as it is pulled through the sensors. Those sensors are similar to Hall effect sensors. They contain magnets on sprung levers, with the strength of the magnetic field corresponding to the diameter of the filament. Each sensor module has its own Microchip ATtiny85 microcontroller dedicated to monitoring its magnet. This type of sensor offers a great deal of sensitivity at a low cost.
With this tester, Sanladerer took detailed measurements of entire spools of filament. He tested Das Filament PLA, Prusament PETG, Creality CR-PLA, Breathe3DP Nylon, and Proto-Pasta PLA. It’s worth noting that those are all well-regarded brands and not the generic stuff you see on Amazon. He found that they all fell within the respective manufacturer’s specified tolerances and were completely suitable for 3D printing. But of the bunch, Prusament was the most consistent. That isn’t surprising, as Prusa Research is a leader in 3D printer development and they know the importance of consistent filament. They started producing their own filament specifically because they wanted to ensure consistency. If you want to measure you own filament, Sanladerer is making his tester design open source so that you can build your own.