[Proper Printing] clearly enjoys pushing the boundaries of 3D printed materials, and sometimes this requires building custom 3D printers or at least the business end of them. Flexible filaments can be a bit of a pain to deal with, simply because most extruders are designed to push the filament into the hot end with a simple hobbed bolt (or pinch roller setup) and only work reliably due the rigidity of the plastic itself. Once you go flexible, the rigidity is reduced and the filament often deflects sideways and the extruder jams. The longer the filament path leading to the hotend, the harder it gets. The dual belt drive extruder (they’re calling it ‘proper extruder’) grips the filament on two sides with a pair of supported belts, guiding it into the hotend without allowing it to deflect sideways. The extruder body and gears were resin printed (but, we checked — the design is suitable for FDM printing as well) proving that resin printing on modern printers, does indeed maintain adequate dimensional accuracy allowing the building of mechanisms, despite the naysayers!
The extruder design took a bit of tweaking, as the belts themselves, were deflecting, but after a few iterations to add some guide rails, it appears to work rather well. Of course we usually don’t get to see all the failures along the way! That withstanding, they started by testing flexible filaments in a logical manner, starting with a minimally flexible filament, with a shore hardness of 93A, before quickly moving onto NinjaFlex (85A hardness) and even successfully printing a gear in an unidentified 60A hardness filament.
The test printer was a Creality CR-10, with a WhamBam Mutant tool-changer installed, so an adaptor plate was n ..
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