PLA is really a fantastic material for many reasons. It is super rigid. It hardly warps. You can print in super high detail. The final part is tough, if printed right. It lends itself to post-processing like sanding and drilling. It is cheap. In a lot of ways, it’s an ideal engineering plastic for 3D printing.
But it also has its failings. It's flammable, it can barely handle 35-40°C temperatures long-term, and it is the single hardest material of any to print, due to its properties before being melted in the hot end. The unmelted filament causes high friction in the feedpath. It’s brittle, and can snap if forced around tight bend radii. It takes a lot of force in the extruder to crush and push the filament through. If not properly cooled, heat can creep up the filament from the hot end to the cold section, and make the filament too soft to push, and this happens at a lower temperature than any other common material.
For all of these reasons, we used PLA as a worst case test for:
- Feedpath friction
- Brittle filament failure
- Minimum feedpath bend radius
- Force needed to crush and push filament
- Extrusion heat creep
All testing to avoid these issues in the Promega was performed with PLA. From there, we expanded our test parameters to ensure all materials worked well, which by this time was very little work, since they all perform better than PLA in these respects.
Because of all this testing, the entire filament delivery and extruder system is a real workhorse. The feedpaths are all optimized to ensure they flow smooth. You can push filament, even PLA, straight through the gear (even when unpowered) all the way to the tip, because it's calibrated to waste so little energy crushing filament. This makes for huge speed improvements, since you no longer have to deal with software and pushing buttons to change filament out. You also get no grinding of the filament on retraction, and no jamming when feeding the start of a new spool behind one that just finished. The nozzle fans are overpowered to handle PLA, so you have to slow them down in some cases to get the best prints. It makes for epic bridging too. Surprisingly, there's still some room for improvement, so we aren't even done yet.
All of this tuning ensures that the Promega works right out of the box, from the first time you hit “Print”. This is not a result getting lucky. Rather, it’s the legacy of a printer that was designed and engineered with an eye to reliability from the start.