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Everything that You can Get about the 3D Printer Extruder

In this guide, you are going to learn about 3D printer extruder from the basics to the complex. This article tells about what’s 3D printer extruder, its mechanism and classification as well as how to choose them for various needs.

What are 3D Printer extruder, nozzle &hot-end? How do they work?

Broadly defined, a 3D printer extruder extrudes materials into desired shape in FDM 3D printer. It’s responsible for both delivering and heating the material. In a narrow sense, an extruder is the part that delivers materials into the heater sink and out of the nozzle.
A nozzle is the part of a 3D printer that deposits molten material through a certain diameter in successive layers. A hot-end is where coldmaterialsis melted and comes out and moves around the print bed to print 3D object.
Many beginners hardly tell what's a 3D printer's extruder, nozzle or hot-end. They usually mix them up. Partly because they’re all close to each other in some 3D printer (it may not).
To understand them, you need to know how 3D printer works.

 

Figure 1 3D Printer work diagram
 
A 3D Printer is building prints layer by layer. An extruder handles feeding the filaments into the heater block where the filament melts. Then liquid filament runs out of the nozzle orifice and solidifies to designated place. Filaments are transited from a cold part to a heated part. So those parts that filaments transferred in a liquid form are named hot-end. Narrowly defined, an extruder offers traction and drive. A nozzle is the gate where filaments come out.
 

Figure 2 Nozzle
 
In a word, an extruder is a part that provides the force to draw filaments into the hot-end and out of the nozzle, a part of the cold-end. In the following article, all extruder refers to the narrow definition.


3D Printer Extruder Mechanism
The 3D Printer extruder almost always takes the form of a round bolt or rod or gear with concave teeth that grip around the plastic filament.

 

 

Figure 4 Extruder
 
Components of an extruder
In the middle of the figure 3, it’s a well machined drive wheel, which usually provides the grip for the filament. It’s mounted on the shaft of stepper motor. The gear together with other parts consists of extruder. (Seen in figure 4 and 5)
 
Figure 5. Components of Creality’s Metal Single Gear Extruder Kit
 
Filament is squeezed into the rod and a gear that are driven by motor. The mere squeeze adds extra force to the filament. A good extruder can grip the filament right. It should not strip or grind the filament. Malfunction in extruder leads to under extrusion and over extrusion. We'll talk about it later.

Different Types of Extruder ——Introduction and Comparison
Extruder has many types, which includes direct drive extruder, Bowden extruder, metal direct drive extruder etc. They generally can be divided by the relative distance to the nozzle, material used and gear numbers.
 

Bowden extrusion system and direct drive extrusion system

Direct drive v.s. Bowden
Direct drive extruder is right next to the hot end. Bowden extruder is seprated from the nozzle and the hot end with a teflon tube connected in between.

Pros of direct drive extruder:
1. Fit for fast prototyping.
2. Great control
on printing flexible material.

Most 3D printer’s direct extruder is right next to the hot-end. Thus, there is more weight in the 3D printer head. Filament is directly in touch with the tube and get into the hot-end, where it melts and comes out of the nozzle. So, there is less fiction and energy consumption. Because of the short distance entering into the heat block, motors in the extruder can maintain the retraction force on the filament. For a flexible filament, this is really a great point. Bowden setup squeezes the filament and grips it into the nozzle through a tube.If there is a long tube connecting the extruder and the hot-end, flexible material can't be squeezed into the hot-end thanks to its flexibility. Even if we add more squeeze in the extruder, it can hardly reach the hot-end.

Another plus point of the direct drive is they can print materials at a faster speed, thus is suitable for large 3mm diameter filament. This is also the same as the last point. It delivers force just right. For the 3mm diameter filament, it’s larger than 1.5mm filaments. There is more downward pressure on the filament, allowing stronger fiction to let it print faster. (The equilibrium condition of forces). Generally, direct drive extruder is grippier than the Bowden setup. It can push flexible filament better.

Every coin has two sides. As the direct drive extruder is mounted on the hot end, there is more weight on the printer head. They can weight
like 8 pounds. That extra weight produces greater momentum during the printing process. This makes the printer head vibration when changing their path.

Tips
: "Momentum equals to weight times velocity. You need to get a small momentum. So you should print in a medium speed, or your print will inevitably get some lines and skipped parts when the printer head changes its path.”

This can also occur in Bowden setup as the inertia of
3D printer head is big. It's not an extrusion problem.

Pros of Bowden extruder:
1. Fit for printing with high precision

2. No lines or skipped steps when changing printing path
3. Great for hard material

Most of Creality’s 3D printer has a Bowden setup, except the 3 in 1 modular machine CP-01 (CNC machining, Laser Engraving and 3D Printing). It’s more precise as the extruder is decoupled from the hot-end and a teflon tube. This is lightweight. It makes the extruder change directions at a relative high speed without worrying change the print quality. But it cannot print flexible material. It may print. But you have to over-grip in the extruder’s gear. It can results in under-extrusion problem in the short run and causes stuck hot-end and nozzle. If you happen to meet those problems, check the under extrusion session below to  get it fixed.

Verdict:
The direct drive is closer to the hot-end while the Bowden setup is remote from it.Direct
drive can handle flexible material better and faster than Bowden extruder. But Bowden extruder prints hard material more precise and fast. Bowden setup has less weight and prints with little lines and skipped steps problem. (And it’s not an extrusion problem. If have, it’s printing too fast or the printer head is too heavy.)This is also why Titan direct drive is so popular. It’s light-weight and durable.

Divided by Material
Extruders can be divided into half plastic and all-metal
one. Most 3D printer extruder is half metal half plastic. They are made of ABS or PLA and can be 3D printed.

Tips: In case the extruder gear is broken, you can print a new gear with plastic filament and STL in 3D printing websites in advance. So, you can get spared gears to change when the extruder’s gear breaks down. Metal extruder is more durable but plastic one is cheaper.”

Divided by Gear Numbers
They usually have at least one gear that is mounted on the shaft of a motor to gear the filament. This is also one of the under extrusion problem comes along. As the gear is too tight and exerts great forces on concave edges. Those edges shave filaments down, causing hot-end blockage and under extrusion.

A dual gear extruder is designed to solve this problem. Two gear transfer the filaments symmetrically. The filament does not glide on the two gears but pushed by tooth. It effectively avoids under extrusion problem.

Note: dual extrusion v.s. dual gear extrusion

This is two different concepts. Dual extrusion means the 3D printer can print with two kinds of filaments, which is great for dual color or hallowed print. It can print with resolvable filament and achieve complex geometry without moving props.

Conclusion
After knowing what extruder is and the mechanics behind, we know a good extruder grips but no strip or grind the filament. Too tight gripping gears lead to under extrusion. Sometimes printing too fast or using a direct drive leads to lines and skipped steps in prints. A metal dual gear extruder is better and more durable than a single gear half plastic extruder. Bowden extruder prints hard filament fast and swiftly. Direct drive is suitable for flexible filaments and can print faster if the print quality isn’t a must-have especially for fast prototyping.