Has anyone seen a good summary of the different types of extruders?

Has anyone seen a good summary of the different types of extruders? I’m printing prusa-i3 parts now, and was just about to print one of the Wade derivatives with the mile long names, but then thought, “well what about direct drive and bowden?”

I don’t think anyone has any overview about any part.
I you find one, let us know!

Are you using 3mm or 1.75mm filament?

Based on my testing, if it’s 3mm, you want a gear ratio of 3-7:1 (assuming 1/16-step drivers, a 1.8-degree motor on the input, and a drive gear with an effective diameter of 10-11mm) to get the right resolution and step rate for the range of speeds your extruder will need to go. This should also get you into the right torque range with a decent NEMA17 like you’re probably using for your other axes. If you decide to go with a geared tin-can stepper like the PG35 (which has fallen out of favor for several reasons, but several similar motors are in use), calculate the step rate and microstepping ratio to match this step rate (roughly 250-650 E steps/mm). Printed-gear motors (wade’s variants, particularly) vary widely in steps/mm (largely because of the inconsistency of hobbed bolts), but on average, they seem to fall within or near this range.

For 1.75, you need 1/3 the step rate, which puts a direct-drive NEMA 17 in the sweet spot with 1.8-degree steps and a 1/16 or 1/32-stepping driver, or a .9-degree stepper with 1/16 microstepping only. Unless you get a really small one, these should also have sufficient torque. I recommend against any gearing for 1.75mm extruders unless you are experimenting with smaller, lighter motors and different drive gear diameters.

@Whosa_whatsis 3mm indeed. Is it because of the increased backpressure in the nozzle that you would want the geared drive there, or just the step rate? Not much of what you wrote there seems to affect bowden or not.

In regards to @Marcus_Wolschon 's comment, where do people think is a good place to document this kind of in flux “what do people do today”? RepRap wiki/blog?

The increased back-pressure means you need more torque. What I said is also true for bowden, but I’m not (yet) an expert on bowden setups, so I don’t have much authoritative information to offer.