Greetings all,
A roller based filament drive was apparently tried (by our founder) before the screw, but had problems (possibly related to the properties of the CAPA plastic?) This may be less of an issue with ABS.
As least one reprapper is working on a roller-drive extruder: [
www.ooeygui.com]
He's also using brass plumbing plugs to make extruder nozzles, which sounds like a good approach (readily available, good heat conduction, relatively less surface exposed to lose heat.)
A key issue with roller drive is that one needs even more gearing down to get into the right feed rate (assuming a drive-roller radius of ~10 mm or greater.)
Offhand, so long as it continues to drive the filament, I don't think flattening is a big issue, so long as the bulging out (perpendicular to the flattening) doesn't hang up in the heater bore. After all, it's going to melt anyway.
If the pellet extruder designs bear fruit, they'll probably win by natural selection, but (IMHO) these ideas are worth pursuing in the meantime. (And pellet feed may prove to be a hard nut to crack.)
-- Larry
