What Does Resolution Mean in 3D Printing? Pt. 1

March 16, 2016 in News

Part 1: Resolution vs. Minimum Feature Size

Technology has been in a resolution war for decades. Televisions recently quadrupled pixel counts from HD to 4K and are poised to do it again soon to 8K. Cell phones, tablets, and anything with a screen will have its resolution as the lead on the spec sheet, provided that it’s something to boast about. But this is nothing new. Resolution wars have been waged since digital technology became popular, and the printing industry was one of the first battlegrounds.

If you were around in the 80’s and 90’s, you remember Canon, Brother, HP, Epson, and Lexmark (among others) battling it out for print speed and resolution. What started at 100x100 dots per inch (DPI) quickly escalated to 300x300, then 600x600, and finally the current industry standard of 1200x1200 DPI. Back then, the meaning of these values was clearly understandable; even the units made perfect sense. Unfortunately, things get more complicated when you add another dimension to printing.

Resolution and 3D printing

High Resolution Star Cube Print
A print’s level of detail is impacted by the resolution in all three dimensions.

In 3D printing there are three dimensions to consider: the two planar 2D dimensions (X and Y) and the Z dimension that makes it 3D printing. Since the planar and Z dimensions are generally controlled via very different mechanisms, their resolutions are going to be different and need to be treated separately. As a result, there is a lot of confusion about what the term “resolution” means in 3D printing and what level of print quality to expect.

High-Resolution Printing

Form 2 Printing Nervous Systems Model
The Form 2 SLA 3D printer has a high Z-axis resolution and a low minimum feature size on the XY plane, allowing it to produce fine details.

What is the resolution of a 3D printer? There’s not a one-number answer. Since they print in 3 dimensions, you will have to consider at least two numbers: the minimum feature size of the XY plane and the Z-axis resolution (layer height). The Z-axis resolution is easily determined and therefore widely reported even though it is less related to print quality. The more important XY resolution (minimum feature size) is measured via microscopic imaging and is therefore not always found in spec sheets. Practically, it means that you should pick a printer that performs well in both categories like the Form 2 does.

SLA vs. FDM

A lot has changed since the first desktop 3D printers became available to the public. Now Stereolithography (SLA) 3D printers, like the Form 2, are competing for the same desktop spots as FDM printers. One of the main advantages that SLA printers hold over their plastic-melting cousins is print quality: SLA printers produce significantly smoother and more detailed prints. While SLA printers can usually also achieve significantly smaller layer heights, the reason for the improved print quality lies in their much higher XY-resolution.

SLA printers produce significantly smoother and more detailed prints.

Unlike FDM printers, minimum feature size in the XY plane on SLA printers is not limited by melted plastic flow dynamics but rather optics and radical polymerization kinetics. While the math is complicated (and outside the scope of this post), it shakes out to this: features on SLA prints can be approximately as small as the diameter of their laser spots. And laser spots can be really small, especially compared to extruder nozzles.

Laser vs. DLP

Within SLA, there are two main types of imaging systems, laser-based and DLP. Unlike DLP printers, which have a fixed matrix of pixels relative to the build area, laser-based devices can focus the laser beam on any XY coordinate. This means that laser-based machines, given high-quality optics, can more accurately reproduce the surface of a part even when the laser spot size is larger than the DLP pixel size. Whichever printer you choose, it should be able to capture the finest details of your creations, from stress test models to photorealistic busts of famous leaders. The right high-resolution 3D printer will bring your designs to life.

This article is Part 1 in our three-part “What Does Resolution Mean in 3D Printing?” series. Read Pt 2: Understanding XY Resolution.

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