Very nice design! I too have made a big delta, but with 1.75mm: to be honest, with a RobotDigg drive gear (check them out, they're got amazing grip, very sharp!) and a modified Wades extruder, it pushes very well, but it tends to chew the filament when I try to go too fast (faster than 200-250mm/s just doesn't have time to melt fast enough in the hotend, so the drive gear scraps away during a millisecond!)- how do you adjust the tension on the filament?
On the other hand, I've been considering trying to make a dual-pinch NEMA 14 direct extruder (with these RobotDigg gears!), as I'd MUCH prefer a direct drive extruder, but on the delta (as you've probably found out) a single NEMA extruder cannot be centered, however, I have yet to sort out the tensioning problem - even if I managed to make it with perfect calibration between the gear teeth, eventually I'd need the ability to adjust extruding pressure (when using materials of different hardness, i.e. NinjaFlex, or Woodpile).... any ideas??
PD All said, still not sure how to get over the limit of how fast the hotend can melt material - I think that once reached that limit, either the extruder drive will miss steps, or the filament will be scraped, as it just cannot go faster - the only thing then is more temperature!