Build your own 3D Printer: Everything about extruders!

Everything about extruders – one of the functionally most important parts of any filament-based 3D printer!

Building a RepRap-style 3D Printer without buying a full kit is still the purist’s way to go – it’s the cheapest and most flexible way of acquiring a 3D printer, but there are a lot of chances where stuff can go wrong. In this mini-series i’ll try to cover the most important spots while Luk builds his iTopie i3!

Everything about extruders!

Hey everyone, Tom here, and when you’re building a 3D printer, you’re going to be faced with a lot of options when it comes to the core of the machine: Its extruder and hotend.

So first off, the extruder and hotend are two distinct parts and their names often get mixed up: The part up here that pushes the plastic filament is what’s called the extruder, technically, it’s just a feeder, but “extruder” is the name that stuck. The hotend – again, what a creative name – is the part that melts the plastic and provides the fine nozzle for it to come out of. In this video, we’re going start with the extruder and all the choices you have there. Well, actually, before we get into that, there’s one crucial decision to be made overall: 3mm or 1.75mm. Filament comes in two different sizes, with 3mm being the more traditional size and 1.75mm as the newer option, well, as long as you don’t count in tech years, and that size can perform just as well with cheaper components, and we’ll touch on that in a second. There is not much of a difference of the print quality you’ll get when it comes to the two different sizes, but it’s looking like 1.75mm filament is becoming the more popular and the new “standard” size. The smaller 1.75mm filament relies more on the filament being pushed quickly and with less force, while 3mm filament moves much slower and with a greater force from the extruder. Both of these parameters are different by about a factor of 3. The larger 3mm filament is better for super-soft flexible filament, but the newer 1.75mm extruders can print it just as well as they support the filament path much more tightly now. Also, of course, don’t get shafted buying filament by the meter – 3mm filament will get you roughly 3 times more plastic per length as 1.75mm filament, but it should also be 3 times more expensive per meter. Should. Sometimes you’ll get charged just as much for 1.75mm per length, which is part of the reason why buying filament by length isn’t really the best option anyways.

I personally run all my printers on 1.75 just because i tend to have filament in that size and it just kind of stuck.

So, that’s the first option you’ll have to pick – while you can convert a 3mm extruder to 1.75mm, which i show you how to do, here, you should get the right size right off the bat, also you can not convert a hotend from one size to the other.

The next big choice is going to bowden or non-bowden. “Normally”, you’ve got your hotend strapped right to the extruder, often even mounted right in there, but, if you’re going for a bowden setup, you’ll have the hotend decoupled from the extruder with a teflon tube. This means there’s going to be less weight to lug around as the hotend moves, but it also means that distance between the extruder and hotend is going to introduce some backlash to the filament drive. If done and set up correctly, it’s not going to be a huge difference for your print results, but a bowden will always tend to print a bit sloppier if you give it the same starting parameters. Of course, the lighter carriage with only the hotend on it will somewhat make up for it as it allows faster acceleration with weaker linear guides and belts, which, in turn, allows you to get crisper results with the same parts.

So next up for the extruder, it’s geared vs. non-geared aka direct-drive. And actually, that decision is rather simple: You # need a geared extruder for 3mm filament, while 1.75mm works with a direct-drive extruder for 99% of all use cases. Geared 1.75mm extruders that use the common NEMA 17 motors are rare, with the E3D Titan, which i’m testing right now being a notable exception, but the gearing doesn’t hurt, either. You should keep the diameter of the filament drive gear in mind for direct-drive types, as they act like a rack and pinion with the filament, so the larger 12mm gears will output less torque before the motor stalls when compared to the smaller 9 or 8mm types. You can’t just make the filament drive gear infinitely small, though, as that will reduce the area the filament is in contact with it and just make it grind through the plastic instead of gripping it. Again, the 8mm types are a good middle ground there for both 3mm and 1.75mm filament. The tooth profile also contributes a tremendous amount to the grip a drive gear will produce – each gear should be sharp, not too deep and have reasonable spacing to the next one. If the teeth are too sharp and deep, they will simply shave off plastic bits from the filament instead of gripping it, if they are too dull, like regular spur gears that are improperly sometimes used, they will just slip on the plastic. And if they are too fine, like ones that are made with an M3 thread all around, they will have a huge tendency to clog up with the tiny plastic particles you’ll inevitably create when driving filament. Coarser profiles tend to have a bit of a self-cleaning effect. I prefer a profile that’s close to something like an M5 screw, but slightly finer or coarser ones will also work just fine.

What also helps with filament grip are the trendy dual-drive extruders, inspired by the Bondtech, that grip the filament from both sides with a driven gear instead of having a flat idler bearing pressing on it from one side and the drive gear only on the other. This tech is entirely optional for regular use, but if you do get an extruder like that, you can be sure that you’ll never have grip issues that don’t stem from a clogged hotend.

So the rest of the extruder’s features are more or less comfort features that make life easier. One of the big ones is an idler that easily unlocks or swivels away and allows you to remove and insert filament without unscrewing anything or having to drive the extruder motor to pull in the filament for you. What can also be helpful is easy access to the drive gear from a cleaning perspective. While i haven’t had stripped filament for many years now, when you’re getting started and maybe haven’t tuned in your printer all that well yet, you might end up grinding through the filament a few times as the extruder fails to push it through the hotend for whatever reason. In that case, you really don’t want to have to disassemble the entire extruder, so a spot where you can get to the drive gear just by opening up the idler or having the drive gear entirely exposed somewhere might save you  good bit of headache. And the last bit should be size and mounting options. While size typically doesn’t matter as long as it fits, you know, it’s more about technique anyways, the mounting options of a particular extruder might be a big selling point. While RepRap-style printers use a de-facto standard mounting pattern, newer designs often can’t easily fit to that. While these mount on top, some printers like the Prusa i3 family, have mounts from the side, and unless your extruder of choice fits directly to those hardpoints, you’re going to have find or design and print an adapter, which can be tricky without a functioning 3D printer. Of course, bowden extruders typically mount to the printer frame somewhere, so that’s a non-issue there.

Now, the good news is that there really aren’t all too many extruders out there that are downright bad. I’d even go so far and say if you’re going for a 1.75mm, PLA-only printer, your extruder choice can be based entirely on comfort features. Or looks. Depending on what you’re going for.

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In the next video of this series we’re going to take a look at what options you have when it comes to hotends and what you should know for picking the one that’s right for you. Thanks for watching, please leave a thumbs down or thumbs up on this video, use the Amazon and ebay affiliate links from the video description for your 3D printing shopping trips and don’t forget to subscribe! I’ll see you in the next one.

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Music is Maccary Bay Kevin MacLeod (incompetech.com)
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