Whether direct drive or Bowden, different extruders work pretty much the same way — the filament is inserted into the extruder, and the motor and gears drive it into the hot end, which will then use electrical heating (e.g., resistance heating) to melt the filament. Finally, the liquified material is evenly extruded out of the nozzle onto the heated bed, stacking up layer by layer to form a 3D object.

Most printers only have one extruder, while some have two. So, which is better — single or dual? If your pocket is deep enough, two is better than one for the most part. In fact, dual extruder 3D printers have become more and more common in recent years, and are even trending to replace single-head printers.

Why are dual extruder 3D printers trending?

Dual color or material combo

Dual extruder can print objects using two different filament colors or types on the same print. This allows more complex and colorful prints.

Snapmaker Dual Extrusion 3D Printing Module mounted on Snapmaker 2.0

Two-color printing is not that uncommon. Even with a single extruder, similar effects can be achieved by manually changing the filament. However, if you want to use two different materials on the same object, for example ABS and TPU to print a flexible/rigid combined object, manually changing filament can be very troublesome, and is prone to failed prints because optimal settings for the two materials are different. Rather than risking it with great effort, it's better to just print them separately and glue them together.

In contrast, when using a dual extruder printer, you can set different parameters for each extruder directly in the slicer software, and complete dual material printing in one print job.

Breakaway and soluble support

The ability to print easily detachable (or “breakaway” as a trade name) and soluble supports is perhaps the primary reason most people buy a dual extruder 3D printer. Removing supports after printing can be tedious and time consuming. And if you don’t do it properly, your print can be ruined by marks, pits, divots or blemishes on the surface finish.

Breakaway support

Breakaway support materials are formulated to have low interlayer adhesion and be mechanically brittle, so they break away cleanly with little force. Soluble materials can dissolve in water or other solvents. PVA (Polyvinyl Alcohol) is the most commonly used one. It is highly sensitive to moisture and decomposes when in contact with water. Taking advantage of this property, it can be used as a support material to fill some difficult-to-reach geometries that allow liquid to flow into. After printing, soaking the print in water dissolves away the supports, leaving behind a smooth printed surface.

Soluble support

Some additional functions

Dual extruders also enable some additional functions, such as a backup mode. In single-extrusion printing, if the active extruder fails or clogs, or the filament runs out, the idle extruder can take over and finish the remainder of the print. This improves overall uptime and reliability.

Improved slicing software

It is mechanically simple to build a dual extruder system by just duplicating parts, but the real challenge is in the software. The popularity of dual extruder goes hand in hand with improvements in slicing software. The slicing algorithms are better at planning optimal toolpaths for dual extruders to minimize travel moves and retracts. They also do well in assigning different model parts to be printed by each nozzle to maximize use and minimize idle nozzles. Software advancements have made dual extruders more user-friendly and reliable, allowing wider adoption.

Drawbacks of Dual extruder

With the growth of the 3D printing industry, desktop printers are more affordable and easier to use nowadays. Dual extruder has also become a common feature on many budget products, allowing more users to experience the benefits of dual printing. However, dual extruders also have some flaws:

Source: Simplify3d

• Cross contamination and collision: In dual-color printing, the idle extruder can ooze material due to residual heat and cause contamination when it glides over the printed part, or even bump into it if the nozzle is too low.
• More maintenance: Twice the hot ends means twice as many parts to check, clean and replace when there are jams or clogs.
• Relatively smaller build volume: Since the extruders themselves take up some length on the X axis, dual-head printers will have a smaller build volume compared to single-head given the same printer frame size. This is especially noticeable when upgrading from single to dual head.

The maintenance and build volume drawbacks are probably unavoidable, but contamination and collision can be solved. The most common way to deal with contamination is setting retraction in the slicer, which prevents oozing by temporarily reversing the filament in the extruder during travel moves.

Another method is using a prime tower — printing another object concurrently with the main print, giving oozing or leaking inactive nozzles a place to purge material instead of on the print. Similar solutions include ooze shield, which surrounds the printed part so any oozed material gets wiped off on the shield when the nozzles are close to the print.

Ooze shield (Source: IceSL)

Some printers also have a wiping device installed directly on the machine at the same height as the nozzle, so the nozzle can wipe off any residual when passing over it. Simple yet practical.

Snapmaker J1s's nozzle wiper

However, these don't solve the collision issue, and prime towers/ooze shields increase time and material usage. In comparison, mechanically lifting the inactive extruder seems more versatile. For example, the Snapmaker Dual Extrusion Module uses motors to automatically raise/lower the extruders, avoiding both contamination/collisions, and allowing fast, quiet extruder switching.

Auto extruder lifting of Snapmaker Dual Extrusion Module

Finally, there is the ultimate solution — an IDEX (Independent Dual Extruder) 3D printer. As the name suggests, the two extruders can move independently. When printing with one head, the other can park inactive in a corner with no need for heating. When both are active, they print independently with no interference. However, to further reduce ooze impacts, IDEX printers may still employ wiping devices, retraction, prime towers, etc. during dual extrusion printing.

Independent v.s. dependent dual extruder system

IDEX has some advantages over regular dependent dual extruders, but also poses some challenges for manufacturers and users.

Snapmaker J1's printing in duplication mode

Advantages

• Minimal contamination and collision: In dual printing, the idle extruder parks in a corner rather than moving along with the active extruder. And before the next printing job, the extruder can wipe off any oozed material using a wiping device or prime tower. So IDEX can effectively eliminate ooze contamination and collision issues.
• Mirror and duplication printing: IDEX printers can double the productivity by printing two mirrored or identical objects simultaneously. Very useful for mass-producing small items like chess pieces.

• Less weight and higher accuracy: Compared to a mechanically linked dual extruder, one single extruder of an IDEX printer is lighter, allowing faster moves with less floating mass and higher accuracy.

Disadvantages

• More difficult to manufacture: Precisely aligning the independent extruder carriages and extruders demands tight manufacturing and assembly tolerances.

• Trickier calibration: Calibration is one of the biggest challenges in IDEX printer design. The two independent extruders not only need to be calibrated with the bed, but also to each other in the X, Y and Z axes. Poor calibration can cause cracks or even print fractures due to poor layer adhesion.

• Higher cost: IDEX not only has higher R&D costs on software, but also requires an independent or semi-independent motion system on the hardware side, including motors and carriages for each extruder. If not sharing an X-axis, additional linear rails, leadscrews or belts are also needed. These factors mean IDEX printers generally cost more than regular dual extruders.

How to choose from single extruder, dependent dual extruder, and IDEX

Here are some things to consider when making the choice:

Single Extruder

• Simplest and most affordable option;
• Easier to calibrate and maintain;
• Limited to single color/material prints.

Dependent Dual Extruder

• Dual color or material printing without much filament waste;
• Allows dissolvable and breakaway supports;
• Costs more than single extruder;
• Potential collision risks and idle oozing issues;
• Trickier calibration.

IDEX

• Can print identical or mirrored objects twice as fast;
• Dual color or material printing without much filament waste;
• Allows dissolvable and breakaway supports;
• Minimal risk of collisions or ooze;
• Highest cost and calibration needs.

In general, for most hobby printing, a single extruder is sufficient. For two color prints or easier support removal, consider a dependent dual extruder. For advanced applications or speed, an IDEX system may be ideal if budget allows. Hope you can find your dream printer!