by orcinus » Sat Mar 29, 2014 4:46 am
Initial tests are very promising.
I might change the hobbed pulley at some point, but otherwise...
The tiny geared 1:50 stepper has more than enough torque to drive a 3mm filament. In fact, i can drive it at currents so low it's completely cold to the touch. Tried extruding in free air at speeds up to 150 mm/s and there were no problems, except about 1mm of slippage per 50mm of filament driven which i'm half convinced was due to the pulley, not the stepper.
Retracts of up to 800 mm/s work fine.
The modified Greg's extruder design also seems to work fine for now. It's not just a stripped Greg's, i've added a hole that fits the base of the shaft on the stepper tightly, to get some load off the two mounting bolts; i've added a space for a 625 bearing (same one used by the V-wheels) so the stepper shaft and its gear train aren't loaded radially; and the filament hole has a conical widening at the top so the filament doesn't snag on it when loading. Things planned: making the idler block slightly taller to decrease chances of bolt slippage, adding an integrated J-head mount and making a sideways-mounting version for mounting onto makerslide (for a Bowden setup).
Gonna test on an actual print tomorrow.