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Extruder Configurations and Preferences

Posted by Trakyan 
Extruder Configurations and Preferences
July 03, 2017 03:58AM
Hey guys, again just wanting an opinion from people, several in this case. I'm not going to get into bowden vs direct drive because that's another conversation and they both have their own fairly obvious purposes and advantages in terms of moving mass and more control over extrusion.

There isn't much to choose when it comes to extruders, but there are still some things to choose. First, geared or not? I know the purpose of geared extruders is to get more torque, but what advantages does this have? Does the gearing mean you can force more filament through the extruder and get higher print speeds? Or does the gearing limit print speeds? From what I understand with direct driven extruders you can reach a speed where there isn't enough force from the extruder to force filament into the hot end and you end up skipping steps. I'm guessing there's backlash but that's fairly easy(?) to account for by increasing retraction. I only have experience with non geared extruders so I can't say, and I'd like some opinions and any experience people can offer.

Another choice is between single and double sided drives. The standard is a single drive gear with a spring loaded idler, but there is also double sided drives where there are two gears which grip and pushes the filament from both sides. You're less likely to strip filament at higher print speeds, but does this noticeably improve print quality or does it have no affect? Most people get by with a drive gear and an idler, do they run into these issues? I personally print relatively slow on my printer so I haven't run into any of these issues. Again, opinions and experiences are really welcome.

Thanks.
Re: Extruder Configurations and Preferences
July 03, 2017 06:10AM
I don't think so.
Re: Extruder Configurations and Preferences
July 03, 2017 06:34AM
What particular part, sorry? I don'f understand your answer
Re: Extruder Configurations and Preferences
July 07, 2017 05:40AM
Just experience and FWIW.

A lot of your questions are dependant on what size stepper motor is attached to the extruder.

I use direct drive with basic single sided sprung (airtrippers bowden) extruder 5.5 kg/cm stepper.
I just use ABS no problem. Blocked nozzle will strip filament not stall motor. Not seen any speed limit.

The diameter of the filament drive gear/hob will act as gearing also. More torque with a smaller one

I don't believe direct extruders would run out of torque at any speed that filament is going thru. Geared extruders are geared down anyway so they run way faster than a direct.

Geared extruders can use much smaller lighter motors is the big plus to them. I've not really heard of any speed issues with them.

Not many double sided extruders out there. Would be an advantage for soft/ flexible filaments maybe offset by reliability and complexitiy of double sided drive arrangement.
Re: Extruder Configurations and Preferences
August 08, 2017 12:22PM
Quote
Trakyan
Hey guys, again just wanting an opinion from people, several in this case. I'm not going to get into bowden vs direct drive because that's another conversation and they both have their own fairly obvious purposes and advantages in terms of moving mass and more control over extrusion.

There isn't much to choose when it comes to extruders, but there are still some things to choose. First, geared or not? I know the purpose of geared extruders is to get more torque, but what advantages does this have? Does the gearing mean you can force more filament through the extruder and get higher print speeds? Or does the gearing limit print speeds? From what I understand with direct driven extruders you can reach a speed where there isn't enough force from the extruder to force filament into the hot end and you end up skipping steps. I'm guessing there's backlash but that's fairly easy(?) to account for by increasing retraction. I only have experience with non geared extruders so I can't say, and I'd like some opinions and any experience people can offer.

Another choice is between single and double sided drives. The standard is a single drive gear with a spring loaded idler, but there is also double sided drives where there are two gears which grip and pushes the filament from both sides. You're less likely to strip filament at higher print speeds, but does this noticeably improve print quality or does it have no affect? Most people get by with a drive gear and an idler, do they run into these issues? I personally print relatively slow on my printer so I haven't run into any of these issues. Again, opinions and experiences are really welcome.

Thanks.

First off, IMO, choosing a geared extruder has nothing at all to do with "push torque". I have yet to see an extruder that couldn't grind the filament to dust when there is resistance! Geared is all about fine control of your extrusion rate. To test this I built a "Thing" that was a 3.54:1 geared extruder and WOW did it make a difference in fine details. I went from 100 steps/mm to 526 steps/mm, a 5:1 improvement in resolution. I saw less "ringing", smaller "zits" and small details that I didn't know were there. Once you have mastered the leveling of your print bed and zero'ing your print head, control of extrusion rates and flow is the next most important aspect of your printer to work on. I say, go for a geared extruder.

The "double side" toothed gears seem like overkill or a solution in search of a problem. Has anyone else seen any particular value in such an extruder? It might be a fun project to engineer up to see what it does...

IMHO, YMMV,
DLC
Re: Extruder Configurations and Preferences
August 08, 2017 03:55PM
Added gearing does increase your torque which is an issue when going fast or when using smaller motors. 20 mm nema 17s cant really keep up at 100+ mm/s on their own, they click and lose steps. Even thicker ~40 mm motors click at higher speed, so gearing is useful for the torque it provides. That being said, good point about the resolution, and I'll keep it in mind.
As for the dual drive gear, it helps prevent filament stripping since you need double the force to strip it now. At higher speeds it becomes useful to prevent filament slipping which can lead to the under extrusion you see at higher print speeds. Tom did a test of the bondtech, a commercial geared and dual drive extruder on his youtube channel and it didnt strip the filament, or stall the motor, the filament kinked in the PFTE tube.

I was looking at gearing and dual drive mostly for their advantages with high speed printing where the motor tends to skipp steps or the drive gear tends to slip. I was looking for solutions to these two problems mainly, but the added resolution from gearing is a nice bonus.
Re: Extruder Configurations and Preferences
August 09, 2017 01:25PM
Quote
Trakyan
Added gearing does increase your torque which is an issue when going fast or when using smaller motors. 20 mm nema 17s cant really keep up at 100+ mm/s on their own, they click and lose steps. Even thicker ~40 mm motors click at higher speed, so gearing is useful for the torque it provides. That being said, good point about the resolution, and I'll keep it in mind.
As for the dual drive gear, it helps prevent filament stripping since you need double the force to strip it now. At higher speeds it becomes useful to prevent filament slipping which can lead to the under extrusion you see at higher print speeds. Tom did a test of the bondtech, a commercial geared and dual drive extruder on his youtube channel and it didnt strip the filament, or stall the motor, the filament kinked in the PFTE tube.

I was looking at gearing and dual drive mostly for their advantages with high speed printing where the motor tends to skipp steps or the drive gear tends to slip. I was looking for solutions to these two problems mainly, but the added resolution from gearing is a nice bonus.

You might be disappointed with geared extruders that are geared too high if you want high-speed extrusions. Your geared extruder stepper has to go 3x to 5x faster to keep up with a non-geared one.You get more torque, true, so you can use a smaller stepper, but if you are looking for speed, you'll need to get a better stepper or stepper driver that can handle more current in order to go faster than a non-geared unit.

Regardless, the resolution gain you get from a geared extruder is so extraordinary that I think it is a no-brainer! I am totally sold, and I just built a simple 3.54:1 geared stepper from Thingaverse, which needs regular maintenance because printed gears wear out. It is worth the hassle! You will have to pay a pretty price for a commercial one, but if it matters, it is worth it.

DLC
Re: Extruder Configurations and Preferences
August 09, 2017 02:02PM
Going faster is a non issue. Extruder motors, even geared ones, are running no where near their top speed when extruding, there's plenty of headroom to go faster.

That and I'm wanting a small, light extruder so a thicker motor is out of the question. A 20 mm motor doesn't appear to have enough torque to extrude on its own, or at least I haven't seen anyone try.
Re: Extruder Configurations and Preferences
August 09, 2017 03:22PM
Quote
Trakyan
Going faster is a non issue. Extruder motors, even geared ones, are running no where near their top speed when extruding, there's plenty of headroom to go faster.

That and I'm wanting a small, light extruder so a thicker motor is out of the question. A 20 mm motor doesn't appear to have enough torque to extrude on its own, or at least I haven't seen anyone try.

You know that's a good point. I was looking at it in a strictly "ideal" world sort of way. As you go faster, your torque falls off. There is no doubt a sweet spot where the torque gained is better than the speed lost and indeed, I don't see my direct drive extruder blasting along at 600 RPM...

DLC
Re: Extruder Configurations and Preferences
August 09, 2017 05:59PM
You're right that as motors go faster they hit a point where torque starts to drop off quickly, however extruders don't run fast enough to have a significant drop in torque. I remember someone mentioning that there isn't a significant drop off in torque below a hundreThe more important thing you lose out on I think is acceleration, your retractions will be slower and not as snappy.

This page on the reprap wiki did some torque testing
[reprap.org]
I'm guessing U/min on the graph is rev/min, so at the sort of speeds an extruder is running there is no significant loss of torque because of the higher speeds required with gearing.
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