today is Sep 28, 2022

A 3D Printer is a sophisticated machine that melts plastic into complex 3D shapes. Upgrading one involves tinkering with complicated motion systems and elaborate electronics, with the added complexity of firmware modification.

That still hasn’t deterred a growing number of intrepid 3D printing enthusiasts from purchasing entry-level 3D printers and modifying them to rival expensive models. One of the most popular mods involves upgrading stock Bowden extruders to direct drive extruders.

It would be fair to assume that upgrading the print head itself would guarantee enough of an improvement to justify the hassle involved. But what if we told you that this expensive upgrade often decreases print quality?

Confused? Read on to find out why an extruder upgrade isn’t as straightforward as it sounds.

Myth: Direct Drive Extruders Improve Print Quality

Visit any 3D printing forum, and you are bound to find members complaining of poor print quality right after upgrading to direct drive extruders. You may attribute some of these cases to faulty upgrade parts and improper installation practices, but these aren’t isolated incidents.

In fact, 3D printing veterans knows that it is virtually impossible for even expensive printers to match the out-of-the-box print quality of the Creality Ender-3 printers. So, what’s happening here?

Anatomy of a stock Creality Ender-3 hot end

But first, let’s take a step back to understand what direct drive extruders are, how they differ from stock extruders, and why they are considered worthy upgrades.

What Are Bowden Extruders?

Popular entry-level 3D printers, such as the Ender-3, ship with Bowden extruders. This print head design physically separates the extruder (which pushes filament into the nozzle) from the hot end assembly consisting of the heat sink, heat break, heater block, and nozzle.

Illustration of Bowden extruder

These extruders get their name from the significantly longer Bowden (or PTFE) tube connecting the extruder to the hot end assembly. This is a relatively simple design that’s cost-effective. But a Bowden extruder’s longer filament path also makes it nearly impossible to print flexible filaments.

You’re essentially trying to push a rope down a hose at that point. And that’s where direct drive extruders come into the picture.

What Makes Direct Drive Extruders Better?

This print head design combines the extruder and hot end assembly into a single unit. The idea is to reduce the filament path by bringing the extruder as close as possible to the nozzle. Doing so significantly shortens the length of filament that needs to be pushed down the PTFE tube. That also means a shorter section of the filament needs to push against the nozzle to generate extrusion pressure.

Illustration of direct drive extruder

A shorter section of filament is inherently stiffer and therefore less likely to bunch up and clog on its way to the nozzle. This allows direct drive extruders to print flexible filaments with ease, while also reducing retraction distance settings for regular filaments. A shorter section of filament is also easier to control with precision, which reduces stringing issues evident in complicated 3D prints.

But Are They Really Better?

Direct drive extruders indeed make 3D printing with flexible filaments a breeze, but virtually everyone nevertheless complains of ugly Z-banding issues after upgrading from Bowden to direct drive extruders. These gremlins manifest as ugly bands running vertically across the print surface and are visible along the Z-axis of the 3D printer.

The severity of the banding can vary from printer to printer, but it absolutely manifests in all direct drive extruders. I have personally used five different direct drive extruders, with each extruder exhibiting this issue to varying degrees.

And it isn’t just me and a few statistical outliers facing these issues.

Consistent vs Inconsistent Extrusion

The Issue #602 Wasteland

The owners of Prusa direct drive printers had a collective meltdown when they realized that their expensive machines couldn’t match the print quality of the considerably cheaper Ender-3 printers. What started as a bug report citing inconsistent filament extrusion, eventually spawned into the infamous Issue #602.

Josef Prusa, the owner and founder of Prusa Research, responded by mobilizing his army of engineers to look into the matter, but the issue remains unsolved to this day. There is an entire Discord community, dubbed The 602 Wasteland, where 3D Printer enthusiasts not only lament and joke about the unsolved phenomenon in equal measure, but some even take a crack at solving the issue.

In short, users are to bound complain about this phenomenon once 3D printers equipped with a direct drive extruder reach a large enough installed user base. Owners of the wildly popular Voron DIY 3D printers (see our Voron beginner’s guide) know this phenomenon as Issue #6. You will find people masking the tell-tale extrusion inconsistency by snapping photos under favorable lighting conditions, but the problem is squarely visible once the 3D prints are shot under overhead lighting.

What Causes These Direct Drive Extrusion Issues?

Once you factor out improper assembly and tuning issues, the leading theories for the inconsistent extrusion associated with direct drive extruders boil down to the Bondtech’s “Dual Drive” extruder gears. These are the exact same straight-cut pinion gears found in virtually every direct drive extruder used in popular 3D printer designs from Prusa and Voron.

3D printing YouTubers Design Prototype Test and MihaiDesigns have done a terrific job of narrowing down the problem to Bondtech’s extruder gears, and the former’s investigation is worth checking out. Both YouTubers have suggested using helical or herringbone extruder gear design to eliminate the inconsistent extrusion issue.

As of this writing, neither Bondtech nor any other extruder maker has brought an improved design to the market, yet.

How Are Bowden Extruders Immune to These Issues?

Do you recall how we had dismissed Bowden extruders by illustrating how their filament feed design is tantamount to pushing a rope down a hose? Well, having that degree of slack, and the ensuing delay in nozzle pressure buildup, is perfect for ironing out extrusion inconsistencies arising out of poor direct drive extruder gear design.

The same design shortcomings that prevent Bowden extruders from having shorter retraction distances—and quicker, more responsive control over nozzle pressure—also come in handy to prevent inconsistent extrusion artefacts from ever manifesting in the actual 3D printed objects.

Ender-3 Stock Print Quality

Take a gander at the clean 3D print (and the lack of Z-banding therein) obtained from my stock Ender-3 printer equipped with the Bowden extruder, if you find that hard to believe. I have used half a dozen different direct drive extruders since then, without ever being able to achieve this level of extrusion consistency.

Not surprisingly, some Voron 3D printer owners still swear by and use Bowden extruders for this very reason. However, doing so has a few caveats.

Should You “Upgrade” to a Bowden Extruder?

You most certainly shouldn’t if you plan on printing flexible filaments, which absolutely need the shorter filament path of a direct drive extruder. Those who own fast CoreXY printers are also better off sticking with their direct drive extruders.

This is especially true if they don't want to sacrifice either speed or the advanced pressure advance feature. It’s impossible for Bowden extruders to pull off advanced nozzle pressure regulation at fast printing speeds. You absolutely need a direct drive extruder to print fast with pressure advance enabled.

Extrusion inconsistency associated with direct drive extruders isn’t the end of the world. Additive printing isn’t supposed to be aesthetically clean to begin with, so minor Z-banding is acceptable.

However, if you are experiencing egregious extrusion inconsistencies, you are better off looking at other probable causes such as bed heat regulation, Z-axis binding, and filament flow rate.

Prusa XL's large extruder drive gear assembly.

Prusa XL’s Cycloidal Gear Extruder to the Rescue

Not everyone is taking this problem lying down. Prusa Research has made radical changes to the new extruder design employed in the upcoming Prusa XL CoreXY printer, as discussed in detail in our primer on the Prusa XL. Many believe that this design could solve the Issue #602 that continues to plague existing Prusa direct drive printers.

It’s a bit premature to get our hopes up with the Prusa XL, but it sure beats continuing to use the same Bondtech direct drive extruder gears suspected to cause the aforementioned extrusion issues.

Direct Drive Extruder Issues

As we’ve explored, while direct drive extruders do make 3D printing with flexible filaments far easier, upgrading to one from a Bowden can result in ugly Z-banding issues.

I have personally made peace with the minor extrusion inconsistencies associated with direct drive extruders in order to reap the benefits of printing flexible filaments, lack of stringing, and being able to print really fast. That’s a fair bargain.

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About The Author

Nachiket Mhatre (20 Articles Published)

Nachiket has covered diverse technology beats ranging from video games and PC hardware to smartphones and DIY over a career spanning 15 years. Some say that his DIY articles serve as an excuse to pass off his 3D printer, custom keyboard, and RC addiction as “business expenses” to the wife.

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