According to this, the problem with grinding materials and re-melting them is that the shear stress from the grinding process makes the plastic unusable, but wouldn't re-melting undo any damage from shear stress? I suppose you might break some polymer chains or something, but I would think that you would have to grind extremely finely for that to be a problem.

After all, isn't most filament (good filament, at least) made by extruding the filament once, then cutting it up (presumably with a shearing cutter of some sort) to turn it back into pellets, to be extruded again? My understanding is that this is standard practice, at least for color filaments, which won't get sufficient mixing in a single extrusion pass. The pellets they show while talking about the shearing problem were clearly made this way...
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