@o_lampe said in Hollow shaft extruder:
@tombrazier said in Hollow shaft extruder:
At 700mA I can drive the filament at 50mm/s and accelerate at 1500mm/s^2 without a motor stall
Is that the retraction speed or can you actually extrude at 50mm/s? What are actual PLA print speeds with 0.4mm nozzle and say 0.3mm layer?
It's always hard to compare apples with oranges, but in the end I'd like to know if it's worth going the extra mile with the dual motor setup I'm working on.
Tom, although I've been using my "original" NEMA 14 VDE for well over two years, I still tinker with ideas. I never could get a NEMA 11 pancake to drive reliably, but TWO of them, rotating in the same direction but mounted back-to-back, seems like the cat's meow. Because they are back-to-back, they eliminate torque on the filament. Of course, you need two motors, and two bearing carriers. But one carrier is "right hand thread", and the other is, of necessity, "left hand thread", so the grooves scored in the filament only cross each other once per revolution. There is no issue with getting the two grooves to track each other, because they can't, and don't need to. They are independent of each other. There is still only one knife edge per carrier, per my reasoning above.
Of course this bumps the complexity and cost by 2x, and the weight up to 65 whole grams! Prototype with 30 degree cant angles.
EDIT Nov.1, 2023: A very brief video of the Push-Me_Pull_You VDE running (change the .doc extension to .mov).
Cons: as noted, twice as heavy and twice as complicated, needs left AND right hand drive carriers.
Pros: handles extremely flexible TPU with no hot end anchoring at all, 5 times the filament force (5 kilos vs 1 kilo) at 0.2 amps (paralleled NEMA 11 motors, no heat issues at all), motors can attain 4500 RPM, and 3000 RPM while actually driving filament (150 mm/sec at 30 degree cant angle). Feed and retraction very repeatable, as the two drivers don't interact.
The Take Away: Not worth the size, weight (80 grams), and expense, unless you are after extreme extrusion speeds. I'll stick to my tried-and-true single knife NEMA 14.
IMG_1951.DOC