@mrehorstdmd said in best practice - limit extruder speed:
@arhi What's the advantage of using an extruder geared down to 40:1
I'm not the one that engineered this one but what I understand is that high gear ration solves the 2 huge problems
backlash
flex in the shaft itself (my old shaft on the 1m length flexes easily half a turn, so half a turn of a motor in one direction and half a turn in other direction and your extruder did not move a bit if you link shaft to a direct drive 1:1!!! actually it will move before half a turn, depends on the force required to move the filament, would move immediately if filament is free but if you hold it by hand it is half a turn. With 40:1 ratio first thing is you reduce this 40 times, so for the same force required to move the hob you have 40 times less play. Then, since you multiply torque 40 times too, the force required to move the filament is 40 times lower so for the same force your flex shaft twist less (I'd say 40 times less but it's not that linear) so let's say, in lamen terms, your "error" is 160 times lower compared to no gearing (it is not 160 times lower, it's lot less but you get my point)
now with regards to "push it slowly", I had some issues with .9 degree motor (totally wrong for this operation) but with some regular 1.8 degree motor, nothing special, 1/16 microstepping I'm able to kill vulcano nozzle without a problem (with duet as it can step fast enough, 8bit boards can't) and I still can drop to 1/4 or 1/2 or 1/1 stepping and get way more speed .. torque required is very low, nema8 can drive 40:1 extruder, and nema8 can rotate very very very fast 😄
p.s. the new shaft is just a tad thicker but is wound differently, it twists lot less than old one so it is even more precise