May 24, 2019

Linear Rail 3D Printer – Really Better or Just a Hype?

3D printers touting high-quality "linear rails" have sprouted up all over the market. Find out if a linear rail 3D printer is legitimately better or just a marketing sham.

Linear Rail 3D Printer What Are Linear Rails?

A cut-away depiction of a linear rail and its recirculating ball bearings. Source: Linear Motion Tips

Linear rails, also referred to as linear motion guides and linear slides, are common motion components used to achieve smooth sliding motions. They can be found in 3D printers, CNC mills, waterjet cutters, and the like.

A linear rail consists of a stiff, steel rail, along which a carriage slide. Most commonly, the carriage contains recirculating ball bearings that provide contact points between the carriage and the rail, as depicted above. This enables a smooth sliding motion as the balls roll between the surfaces. The shape of the shaft enables the carriage to stay locked on with tight tolerances, restricting the motion to strictly linear directions.

Linear rail 3D printers utilize the numerous advantages of these linear rails to, supposedly, achieve better motion. So, how plausible are these claims? Let’s take a look.

Linear Rail 3D Printer Advantages

Only one rail used to support a print carriage. Source: Thomas Sanladerer / YouTube

Most 3D printers sport hardened-steel linear rods, used in tandem with linear ball bearings. This combination has worked well for thousands of printers and users, so what more do linear rails bring?

  • Linear rails are stiffer. Linear rails flex significantly less than linear rods, due to factors such as shape and metal stiffness. Not convinced? Try bending one yourself, and compare it to a typical linear rod. Any decent rail will have far less give. In terms of 3D printing, this leads to greatly reduced backlash and ringing artifacts, yielding cleaner print surfaces and edges.
  • You can get away with one linear rail. Unlike linear rods, linear rails don’t allow for any rotation of the carriage. This means that, when setting up a motion system, a single rail can achieve strictly linear motion on its own, as shown above. With linear rods, at least two are necessary to prevent rotation, leading to complications with proper alignment and introducing weight considerations. Using a linear rail can create a simpler, lighter, more nimble assembly, which will also reduce 3D print ringing.
  • Higher precision, smoother motion. Linear rails are also usually manufactured to much tighter tolerances than linear rods. This higher precision translates to reduced play and binding (when the bearings catch and don’t roll smoothly), yielding smoother, more consistent motion.
  • Easier, more precise mounting. Linear rails are much easier to mount than rods. The rails and carriage both have regularly spaced mounting holes, so a couple of bolts will have everything locked down. This contrasts sharply with linear rods and bearings, whose round shapes require more creative, and often less precise, mounting solutions in 3D printers.

Linear Rail 3D Printer Disadvantages

High-quality linear rails are several times more expensive than typical linear rods and bearings. Source: Thomas Sanladerer

Of course, nothing is perfect. In a few areas, linear rails fall short of rods in 3D printer applications.

  • Linear rails are expensive. There’s no getting around that. Any decent linear rail will easily cost several times more than a comparable combination of linear rod and bearing. The premium precision, stiffness, and smooth motion come at an equally premium price.
  • Linear rails must be handled with care. Unlike round linear bearings, the ball bearings in linear rail carriages aren’t usually capped and locked in. If the carriage accidentally falls off the rail, some ball bearings may roll out, leading to inconsistent motion.

Linear Rail 3D Printer Popular Linear Rail 3D Printers

The Cetus 3D printer with linear rails. Source: Cetus3D / Kickstarter

So, in practice, how do linear rail 3D printers fare?

In the DIY scene, many users have “upgraded” their Prusa-style 3D printers, such as the CR-10 and Anet A8, to linear rails. Picking linear rails for CoreXY motion systems is also common. In both cases, the rails’ ease of mounting and smooth motion lend them much of their appeal.

In commercially-available machines, linear rails have found their way into acclaimed 3D printers from Markforged, Atom, Cetus, and E3D, just to name a few. All of these machines take advantage of linear rails’ superior motion. As an example, the Cetus (depicted above) also takes advantage of the lack of rotational movement and incredible stiffness of these rails, enabling a more inexpensive, bare-bones motion system. It demonstrates the potential of linear rails in weight and material reduction.

Thus, while most 3D printers still use linear rods and bearings, linear rails have definitely seen success on the market, playing to their known advantages. The marketing around these rails definitely aligns with accurate facts and the experiences of users.

Linear Rail 3D Printer Verdict

The premium E3D Toolchanger sporting linear rails. Source: Thomas Sanladerer

Linear rail 3D printers have a lot going for them. But are they really better?

From a pure performance perspective, yes, linear rails are truly superior. They offer greater precision, better mounting, and smoother motion, improving print quality and printer reliability. With good design choices, weight and cost savings are also possible, as demonstrated by the Cetus 3D printer.

There is, however, an elephant in the room: the price. Traditional linear rods and bearings are perfectly usable at just a fraction of the cost, making linear rails difficult to recommend to everyone. If you’re on a tight budget and don’t need the best possible performance, linear rails may not be the best choice.

Thus, we have our verdict: Linear rails are better. They’re just not for everyone.

Feature image source: Cetus3D / Kickstarter

License: The text of "Linear Rail 3D Printer – Really Better or Just a Hype?" by All3DP is licensed under a Creative Commons Attribution 4.0 International License.

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