I have come across a NEMA 34 stepper, and I thought it might be fun to build an extruder around it. It's an M091-FD03, described
here (look on page 3, third line down, at the "bipolar" section).
It would be Bowden, because I have a delta, and it probably couldn't even
lift the motor. On the other hand, the excess torque (about 180 oz-in holding) would let me use a large drive gear to get better grip, and would prevent any skipped steps.
Problem 1: the drive gear. The shaft has a 14mm diameter, which is larger than the ODs of every drive gear I've seen. Unless I can find a larger one and bore it out, this means I have to either machine my own gear and design my own extruder, or attach a "shoulder shaft" to reduce the diameter. Or perhaps I could use a geared or belted extruder, in which case only the drive gear or pulley would need modification.
Problem 2: the electronics. This is actually pretty small as NEMA 34's go, but it still wants 3.3A, which is twice what my DRV8825's can give. Are the cheap Toshiba drivers on eBay really that bad?
Problem 3: the design. I can only find one NEMA 23 extruder design out there, and it's designed for a MK8 drive gear, which would be unnecessarily small even if the shaft would fit. So, I must either design my own extruder, scale up / modify a NEMA 17 design, or use an adapter plate -- and I suspect the latter option would break the extruder if I'm not careful.
Or I could just save the thing for the Z-axis of my next machine...
