All About Extruders and Nozzles

At its basest, the cold end consists of a stepper motor, some form of toothed gearing, a hobbed bolt or gear, spring-loaded idler (typically a bearing of some kind) to hold onto the filament and then PTFE tubing to guide the filament. With the exception of the PTFE tubing (which is not necessary on a direct drive 3D printer extruder), this cluster of parts is the same in both direct drive and Bowden 3D printer extruders.

The humble stepper motor — seen here with a metal gear essential for the 3D printer extruder — these drive the motion and extrusion of filament in most if not all modern desktop 3D printers. Stepper motors are brushless DC motors that achieve a high level of precision in small movements and impart full torque at low speeds. Exactly what one wants when pushing exacting amounts of filament around a 3D printer extruder.

The stepper motor alone is not enough to feed filament to the hot end though. Parts attached to and working with the stepper motor’s driveshaft are required to physically grab the filament and push it along on its path to the hot end.

For this, there is usually a combination of gears and hobbed bolts or shafts (in the image above, we see a hobbed shaft attached to a plastic gear) serving as a pinch wheel along with a bearing or other stiff frictionless material. Often spring-loaded to maintain pressure on the filament, this also allows for the free movement of the filament (as dictated by the rotating of the hobbed bolt/gear). This arrangement typically sees the stepper motor directly pushing on the filament to feed it.

Alternatively, there are versions of the 3D printer extruder cold end that utilize slightly different part arrangements in order to feed filament. Such variances often claim to offer increased grip and delivery of the filament.

One such example would be Bondtech and its popular 3D printer extruder. It uses two geared counter-rotating hobbed gears to grip the filament from two sides. The result is a dramatic increase in grip power when pushing the filament.

As mentioned, there are variations of 3D printer extruder that utilize these parts in slightly different arrangements from one another. Each has its own pros and cons. Next, we’ll dive into what the differences are between direct drive and Bowden 3D printer extruders.

A direct drive 3D printer extruder is distinctive for its placement of the extruder motor directly on top of the hot end. Such an arrangement minimizes the travel distance of the filament to the hot end and can allow for more reliable 3D printing of flexible filaments.

Note though that because a 3D printer has a direct drive extruder does not necessarily mean it can print flexible filaments — soft wiggly filament can and will find its way out of an unconstrained paths. For success printing flexible materials, pay more attention to the position of the pinch and the path immediately around in inside your cold end.

A benefit to the use of direct drive is the finer control of retraction. Because of its position directly over the hot end, there is less travel between the pinch action and the filament passing through the heatbreak into the hot end. Consequently, there is less room for the filament to bend and buckle under the pressure exerted on it.

You will find a direct drive 3D printer extruder contributes to a bulkier, taller print head. Since it is adding a motor and other parts on top of the hot end, it logically stands to reason that this system is also adding mass to the print head, necessitating the build of the printer around it to accommodates moving this extra mass accurately.

A poorly assembled printer with a direct drive extruder is more likely to exhibit poor print quality (likely ripples on the surface of the print) from the print head’s continual overshooting and lurch when changing direction.

Describing the difference between the Bowden and direct drive 3D printer extruder is easier if we turn to a clumsy metaphor. Everyone loves a clumsy metaphor, don’t they?

Imagine the difference between standing a few feet away from a hole in the wall and trying to poke a pool noodle through it, then standing inches next to the wall to do the same. One gives ample room for the noodle to wobble, bend and buckle. The other does not.

Rather than being mounted directly on top of the hot end, as with a direct drive 3D printer extruder, the Bowden style of 3D printer extruder sees the assembly of motor and gearing mounted to the printer’s frame. In doing so, the Bowden extruder gains an advantage over its print head mounted direct drive sibling: speed.

Mechanically a Bowden 3D printer extruder is no different to a direct drive 3D printer extruder. You still have a stepper motor driving a hobbed gear/bolt, which bites into the filament passing through it. Since the filament now has some distance to cover before entering the hot end for melting, the use of PTFE tubing is necessary to guide it. This tubing, typically with an internal diameter slightly larger than that of the filament, constrains the material’s path and allows the cold end to exert pressure as it feeds.

By placing the mass of the 3D printer extruder on the frame instead, a the print head is freed up to print at higher speeds without sacrificing print quality. Less mass moving at speed on the print head means

A side effect of positioning the 3D printer extruder in such a way is that now the filament has a long way to travel within a tube that is a fraction wider than it is. Across the length of the tube, there can be enough room for the filament to bend slightly. When retracting the filament between travel moves, this slack in the filament eats into the retraction distance. Without correction (i.e. increasing retraction), this introduces a delay in the easing of pressure effected on the hot end. In short, you could get messy stringing if you don’t take care to alter your retraction settings.

Another issue to address with Bowden 3D printer extruder setups is friction. With the filament needing to be pushed long distances inside a tube, it’s important that sufficient bite from the extruder with enough torque behind it is exerted on the filament for it to reach the hot end. Because of this, it’s not uncommon to see geared extruder motors in Bowden style 3D printer extruders for the higher torque they offer.

Most delta style desktop 3D printers utilize Bowden extruders.

A common argument that crops up when discussing a given 3D printer extruder is its ability to handle flexible filaments. Which is better? Bowden, or direct drive?

Such arguments likely arose from the development and availability of flexible filaments for 3D printing, and their attempted use in 3D printers designed before such materials was a consideration. Because of this, a stigma around Bowden extruders and their supposed inability to print flexible filaments grew. But on today’s machines, that’s mostly not true.

Any extruder is capable of pushing or pulling wiggly flexible filaments. The problems arise when that filament is unconstrained at any point beyond the pinch point of the extruder. This is a design quirk present even on some direct-drive extruders.

Materials such as TPU are soft and wiggle like cooked spaghetti, so require better guidance through the 3D printer extruder to avoid buckling on itself and wrapping around moving components. If you’re looking to print flexible filaments, there needs to be as little open space from where the filament is gripped by the hobbed gear and bearing, and its entrance into the heatbreak.

That should be about it with regards to the 3D printer extruder and printing flexible filaments. But that alone isn’t enough for success — there are print settings you must consider that will ensure it, such as speed and retraction.

Where the cold end directly manipulates the filament, pushing and pulling as required by the 3D printer, the hot end is where… well, the hot stuff happens.

Inside the assembly known as the hot end the filament passes into a heated chamber, where it transitions from solid to liquid. Sounds simple, and it mostly is. Though there is a lot going on to allow the filament to silkily extrude onto your build plate.

From the top to bottom, your typical 3D printer hot end comprises of a specific sequence of parts. There is a slight difference depending on if you are using a PTFE/PEEK or all-metal hot end. Here we explain the all-metal hot end — a breakdown of the differences between PEEK/PTFE and all-metal hot ends can be found in the section below this.

Firstly there is the filament feed tube (not pictured above). In both the Bowden and direct drive 3D printer extruder this will simply be the PTFE tube running from your cold end. Though note that not all direct drive 3D printer extruders feature this.

Sometimes you’ll see direct drive 3D printer extruders with the filament running directly into the print head.

On a Bowden 3D printer extruder, this feed tube inserts the filament directly into the heat break through the heat sink. The heatbreak, which is threaded into the heat sink, is often simply a threaded stainless steel (or other non-heat conducting metal, such as titanium) tube.

Divided into two parts (notice the two separate threads on the image below — longer for the heat sink,  shorter for the heater block) and featuring a treated interior surface, the heat break allows the filament to pass freely into the nozzle for extrusion.

But, since we’re dealing with accuracy and material that turns into a liquid to be rapidly re-cooled, the management of temperature is crucial. The heatbreak, in combination with the heat sink, maintains a specific boundary at which the filament is hit with high temperatures.

The upper portion, which is actively cooled by the heat sink and a dedicated fan (or water cooling system, in some extravagant cases), prevents heat escaping the hot end and weakening the filament before it is where it needs to be for extrusion. This undesirable phenomenon is known as heat creep.

The lower portion of the heat break sits within a heater block, along with a heater cartridge, temperature relaying thermistor, and nozzle.

Usually constructed from aluminum, the heater block ensures a seamless transition for the filament from the open end of the heat break tube, into the nozzle.

The temperature to melt the filament has to come from somewhere though, which is where the heater cartridge comes into play. Under an electric current, the heater cartridge gets hot, transferring heat to the nozzle via the heater block they are both encased in.

Power resistors are an alternate means to heat the hot end, but are less common these days.

Also housed within the heater block is a thermistor — a small probe that relays the temperature of the block to the 3D printer’s mainboard, allowing for the correct adjustments to be made. In layman’s terms (we’re not electrical engineers here — it’d be disingenuous to attempt to explain in detail), it does this by nature of its resistance changing in correspondence with its temperature, and thus the printer’s board can get a read on the temperature based on the resistance at that current point in time.

And then, at the raggedy edge of the whole system, there is the nozzle. A small nubbin of machined metal, the nozzle itself consists of a chamber — where the molten filament resides — that tapers to the nozzle’s opening.

This opening is a precise diameter, which is the measure by which you purchase it. Most desktop 3D printers ship with 0.4mm nozzles as standard, but there are many other sizes available.

Brass is the preferred material for factory-shipped default nozzles but, while fine for softer materials like PLA and ABS, filaments with tough additives such as carbon fiber will quickly wear away and deform a brass nozzle’s opening. For specialist filaments, 3D printer nozzle materials like stainless steel and ruby are preferred.

The 3D printer nozzle is a veritable world of options, so we’ll detail the popular choices and differences between them below in their own dedicated section.

In a nutshell, there’s little to understanding the 3D printer nozzle. Screwed into the hot end heater block, a small chamber lies within. Filament travels from the cold end into the hot end and through the heat break where it meets the nozzle.

This transition into the heater block is where the filament liquefies. From here it is channeled through the 3D printer nozzle to a taper ending in the nozzle opening.

There are two main considerations when it comes to 3D printer nozzles: the diameter of the opening and the material of the nozzle.

On your average out-of-the-box desktop 3D printer you’ll find a 0.4mm nozzle. And chances are it is made from brass. This is fine and dandy for printing run of the mill materials such as PLA and ABS, but when you start to look further afield at exciting materials like glow-in-the-dark PLA, or metal-enriched filaments, the softness of brass becomes an issue.

With the continual extrusion of filaments that contain hard particles, the 3D printer nozzle gradually erodes. Over time this distorts the opening and inner dimensions of the nozzle, reducing the consistency of what is extruding from the nozzle at a given time and impacting on print quality. It is for this reason that 3D printer nozzles made from harder materials are preferred for such usage.

Here’s a rundown on some the 3D printer nozzle materials kicking about the market these days:

BRASS 3D PRINTER NOZZLE

The “standard” 3D printer nozzle material, and most likely the nozzle type that came on any desktop 3D printer you bought recently. Of the 3D printer nozzle materials, it is the softest around. Easily machined, brass nozzles are cheap and widely available, making it the ideal stock nozzle. Its excellent thermal conductivity also makes it the material of choice for exotic nozzles that use a different harder material for its tip.

Characteristics:

• High thermal conductivity
• Resistant to corrosion
• Relatively soft
• Low abrasion resistance

Best uses: “Soft” plastic filaments such as PLA and ABS and PETG. Filaments that do not include particle additives (metal and carbon fiber, for example.)

STAINLESS/HARDENED STEEL 3D PRINTER NOZZLE

Harder than brass, multiple forms of steel can be found in use as 3D printer nozzles today. Typically stainless steel or hardened steel, these materials allow for the long term printing of filaments enriched with hard particles like carbon fiber and metal without the risk of the 3D printer nozzle eroding and print performance suffering.

One downside to steel as a 3D printer nozzle is its poor thermal conductivity compared to brass. This can mean inconsistent flow performance, especially so at larger nozzle sizes.

Characteristics:

• Low thermal conductivity
• Resistant to corrosion
• Relatively hard
• High abrasion resistance

Best uses: Filaments laced with hard additives such as metal, carbon fiber, and glass.

RUBY 3D PRINTER NOZZLE

There is a glut of other materials used for 3D printer nozzles, some more exotic than others.

The Olsson Ruby is one such nozzle. Developed by Anders Olsson, a research engineer at Uppsala University in Sweden, it is the result of a requirement for a specific experiment 3D printing a filament blend containing Boron Carbide. After as little as 1kg of the filament, standard brass and steel nozzles wore down to unusable distortions of their former selves.

And so Olsson created the Olsson Ruby. A brass nozzle with a ruby tip, it retains the thermal conductivity of brass and pairs it to the superior abrasion resistance of ruby (specifically aluminum oxide).

It could be argued that the ruby element itself in the Olsson Ruby nozzle has a low thermal conductivity, making less reliable in some instances, but there is little chatter online to back this up.

Characteristics

• High thermal conductivity
• Resistant to corrosion
• High abrasion resistance

Best uses: As with steel, highly abrasive filaments are the prime use case for a nozzle like the Ruby. The one difference here is that it was specifically designed to print the third hardest material in the world, without giving up the ghost after a few hundred grams of material.

OLSSON RUBY NOZZLES

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TUNGSTEN CARBIDE 3D PRINTER NOZZLE

A relative newcomer to the 3D printer nozzle market is the Tungsten Carbide nozzle. Produces by Canadian manufacturer DyzeDesign, it is inspired in part by the heavy mining industries and their use of the ceramic for cutting metals and drilling rocks. Tungsten Carbide strikes a balance of hardness, abrasion resistance, and thermal conductivity.

Real-world testing of the nozzle is few and far between, however, since it currently stands as a Kickstarter campaign with the delivery of the nozzles pegged at late 2018.

Characteristics:

• High thermal conductivity
• High abrasion resistance
• Hard
• Resistant to corrosion

Best uses: Billed as the best “all-rounder”, a Tungsten Carbide 3D printer nozzle would more than comfortably deal with the abrasive filaments that demand a tough nozzle.

The nozzle diameter impacts upon how fine a level of detail you can aim for in your prints, affecting not only on how wide your line widths are, but the recommended layer heights, too.

For starters when printing with a 0.15mm 3D printer nozzle versus a standard 0.4mm nozzle there is the obvious advantage of being able to theoretically achieve higher X- and Y- axis resolution. Finer lines can mean sharper corners, however we will say this gain is likely only achievable on a well maintained and tuned 3D printer.

That’s not to say you shouldn’t consider a smaller nozzle for your prints if you don’t feel your machine is as precisely tuned as we mention above, as there is another advantage in the reliability in printing finer layer heights.

As a loose rule of thumb the 3D printer nozzle diameter should dictate the layer heights you aim for. Aim to be printing layer heights approximately 25-50% of the nozzle’s diameter.

This (along with a properly calibrated bed) ensures better adhesion between the lines you lay down. For example with a stock 0.4mm 3D printer nozzle, you should aim to be printing with a 0.1 – 0.2mm layer height.

So, to have a better chance of successfully printing superfine layer heights below 0.05mm, you might be better served opting for a 0.2mm 3D printer nozzle. Like any thumb though (and its rules thereof), it bends. Your mileage may vary and experimentation with your print settings will no doubt accommodate successful prints outside of this rule.

One downside to using smaller nozzles is the likelihood of clogs. A smaller 3D printer nozzle opening, by nature of having a smaller path, more likely to get clogged by particles that would otherwise flow through a larger nozzle. Be prepared for the possibility of regular cleaning and unclogging.

Adding to the possible drawbacks of using a smaller 3D printer nozzle is the dramatic increase in print time, with more passes of the print head required to cover the same distance a larger nozzle would achieve in fewer moves.

On the other side of the coin for 3D printer nozzle sizes is increasing nozzle size. Doing so can have a pronounced impact on your print for the better. Wider extrusions can cut print time exponentially — a single 0.8mm wall takes half the time of a 0.4mm wall that is two lines thick, for example.

In addition, larger line extrusions bond better, resulting in stronger prints. These advantages make large 3D printer nozzles a boon for fast prototyping where fine surface detail is a low priority.

Of course, the downside of printing larger extrusion lines comes at the expense of definition in your print. It logically stands the fatter lines of extruded plastic will render fine surface detail poorer than smaller nozzles.

You could argue that the benefits of using small nozzle sizes are limited to hobbies and professions that demand fine detail, most likely model making and jewelry design. For the average Joe, there’s probably little reason to go finer than 0.4mm (there’s a reason it’s the standard stock 3D printer nozzle size.)