Extruder drive direct or geared

bcdist · 27 Oct 2020, 00:47

I am finalizing constructing a Duet2 system.
I have a dual extruder to setup and have a choice of either using 2 x 17HM19-2004S (0.9deg) direct drive that will give me 188 e-steps per mm at 16 micro-steps or 2 x 17HS19-1684S-PG5 (1.8deg) geared drive that will give me 488 e-steps per mm at 16 micro-steps.
Notting that the geared drives will add a little extra weight to my carriage and I have make a 20mm coupling for each of the geared drives, and modify the design my carriage.
Is it necessary to go for the greater steps? or put it another way - Would I have a better printer with 488 e-steps per mm for my extruders or is 188 good enough for 1.75mm filament.

Phaedrux · 27 Oct 2020, 00:51

It's a bit of a toss up. Geared 1.8 degree will give you more pushing power, but if you stay within the melt rate limits of your extruder that won't really matter.

The Ender3 stock extruder has only ~90 steps per mm and you can get exceptional prints from it, so more steps per mm isn't always better.

So it sounds like maybe in your case the ungeared direct drive might be the easiest and lightest option.

If you wanted, you could increase the microstepping from x16 to x64 to gain a bit of resolution if you're printing things with very small features.

jens55 · 27 Oct 2020, 01:06

My two cents:

Both direct and geared drives are available with a single drive gear or a double drive gear. Single drive gears have a single serrated wheel that pushes the filament the double drive gear uses two serrated wheels with the filament being pushed by both serrated wheels.
While I prefer a geared extruder, I think it is more important to make the distinction between single and dual drive system.
I HIGHLY recommend a dual drive arrangement.

IMHO, geared extruders are better for printing small details and at the same time I have not run into a situation where I could not push filament at my maximum melt rate of the nozzle. In other words, I don't see a disadvantage in a geared extruder.

theruttmeister · 27 Oct 2020, 01:18

I've not seen anyone conclusively demonstrate any print quality advantage to geared extruders. The primary reason for using them is to generate enough torque.
If you are using 1.75mm that's less critical (although there are a lot of hotend designs that end up needing geared motors due to poor design).

I have a machine that I have run both with a direct drive NEMA14 and a 10:1 NEMA11. I can't tell the difference between the print quality of the two options.

If you are planning on running very small prints with a tiny nozzle, it might make a difference.
A properly designed single drive can easily provide enough force, but there not that many of those. Dual drives are a lot more forgiving of things like poor drive gear design and can help if you are using a hotend that requires more extrusion force.

If its a machine of your own design, direct drive might save enough space that its worth it over geared. Plus the geared motors are a little more expensive.

jens55 · 27 Oct 2020, 01:35

I should clarify - I have a 800 mm or so feed tube from the extruder to the nozzle and was having issues with the un-geared and single drive roller original extruder.
It took me a while to determine what the issue was and I am completely converted to the dual drive geared extruder setup.

bcdist · 27 Oct 2020, 03:12

Thanks Guys, you all have given me more to think about. The geared 17HS19-1684S-PG5 stepper motor is only US$30, so cost is not an issue. (The extra weight is about 200g each motor) I have a large bed 500x500. and may need to allow to upgrade to a dual drive geared extruder feed in future.
If I don't change my design to the geared system now, I will not have the space available be able to upgrade.

jens55 · 27 Oct 2020, 03:26

Ummm .... I am sorry, Imust have missed something here ..... I use a standard motor and the extruder is geared. No extra weight for the motor and the extra weight for the extruder is probably less than 50 gr.

I skipped right over that aspect in the original post .... it sucks to get old

bcdist · 27 Oct 2020, 03:27

I have decided. I've worked out a way to modify my design a little to use my existing stepper motors with the dual extruders for now and allow for a geared motor and dual drive gear in the future. thanks all