Understanding all the hype around what “quality” filament means can get confusing. We wrote this blog to help bring some clarity on what our definition is and what it means for you. This is a two-part blog series. The first part is a background on the extrusion process to get the newcomers up to speed. If you already have a solid grasp of the extrusion process, then proceed to the second part now.
The Filament Making Process
When investigating the quality of 3d printer filaments, you may have noticed advertisements that look something like ± .05mm or ± .03mm tolerance. Or maybe you have even seen those numbers printed on your spool. What exactly do these numbers mean? In this blog post, we want to help clear up some confusion on what a quality filament is and what to look for before purchasing filaments online.
The first and very important step or pre-step in the filament making process is to dry the pellets. Filament manufacturers need to make sure there is no moisture in the pellets. Most plastics are hygroscopic by nature (absorb moisture out of the air) which causes problems in the extrusion process. Exposure to very high temperatures causes the water to evaporate from the plastic which creates bubbles in the filament. Not good. Different plastics require different levels of drying all determined by the manufacturer of the filament.
After Drying, the filament manufacturing process begins with an extruder. The extruder is what melts the plastic pellets down to a semi-molten state so that is can be pushed out through a nozzle. The push comes from an extrusion screw that takes the melted pellets through a heat/pressure process that passes the material through the different heat bands in the extruder. Filament manufacturers often refer to the various speeds, heat temperatures, and settings required to successfully make a batch of filament as a recipe that can be saved and stored in a computer for easy recall later.
Once the filament leaves the extruder out of the extruder nozzle, you now have filament that must be pulled to the correct size. Adjustments in speed and tension is what correctly shapes the filament to 1.75mm or 2.85mm sizes. Before the filament reaches the puller, however, it goes through a water bath to cool the filament through a series of chambers that bring the temperature down at a controlled rate. Different filaments respond differently to the puller speed and tension as well as the water bath, so this process is also considered part of the recipe for creating filament.
So how well did we do? Is our recipe right? There are certainly several measurements and checks along the way in each of the above steps. But the one true final step, or the last check before the material gets wound onto a spool, is for the filament to pass through a laser inspection system. It can detect how far off the filament is from the set size of 1.75mm or 2.85mm. The laser system reports back to a computer that shows in real time what those measurements are and can sound an alarm if the filament moves out of spec. Specifically, the laser is measuring diameter and ovality of the filament.
The other thing to consider is how often is the laser checking the filament? Once, twice, three times a second, ten? As time passes, more filament is running through the machine so if you wait too long to check, it is possible your inspection system can miss a section of the material! This is a very important metric that unfortunately a lot of filament manufacturers are not reporting on.
More on Diameter and Ovality
Most people are likely familiar with what the diameter of something means. If you could cut out a cross section of the filament and measure from one point to the other at exactly 180°, you would have the diameter. An easier way to measure your own filaments diameter is to use a pair of calipers to give you a read out on what the diameter of the material is.
Ovality is basically determining how round the filament is. If you divided up a circle into 360° and measured just 1 degree from one end of a circle to the 180° opposite, you just measured the diameter. But if you measured every single degree and got a diameter, you just measured the complete roundness or ovality of the filament at all points along the circle of the filament (measuring 180 times would be all that is needed since you are measuring two points to get a diameter, 180 x 2 = 360). Good luck doing this manually…
Why do diameter and ovality matter, you ask? If you have a filament that exceeds spec, you are going to clog your printer or possibly over extrude. If you have a filament that is under sized, the teeth in your printer may have a hard time gripping the filament or you may under extrude the filament.
Another big problem in poor filament quality shows up for the manufacturers of 3d printers. 3d printer manufacturers must allow for large tolerances of the filament to pass through their machines because everyone has different standards of what quality filament is. A 3d printer manufacturer runs a great risk if they wish to develop a machine with very tight tolerances. They have to account for all the wide variability in filaments despite their interests being aligned to bring the tolerances in as tight as possible, so their printer can print high quality prints!
What is High Quality Inspection?
When we began this blog, we asked the question, what does ±.05 or ±.03 etc actually mean? Does a lower number mean higher quality? The ± symbol means how far above or how far below the filament is allowed to exceed the set spec of 1.75 of 2.85 off the manufacturing line. As an example, the allowable ranges for both filament sizes, at ±.05 would be:
|1.75mm Filament @ ±.05mm||2.85mm Filament @ ±.05mm|
|High||+ 1.80mm||+ 2.90mm|
|Desired||= 1.75mm||= 2.85mm|
|Low||– 1.70mm||– 2.80mm|
|1.75mm Filament @ ±.03mm||2.85mm Filament @ ±.03mm|
|High||+ 1.78mm||+ 2.88mm|
|Desired||= 1.75mm||= 2.85mm|
|Low||– 1.72mm||– 2.82mm|
The filament with the lower tolerance rating of ±.03mm appears to be the desired purchase, but there is way more to the story than that. We need to know how many lasers are being used to make the measurements. How well is the laser inspection system actually seeing the filament? Can 1 laser see all of it? What about 2 lasers? The right question to ask, is, how many lasers do I need to see what percentage of the filament that I feel confident is good filament. To answer that question, continue to the second part of our blog. Fair warning, it is highly technical in nature.