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What Does Resolution Mean in 3D Printing? Pt. 2

Part 2: Understanding XY Resolution

Read Part 1 to learn about resolution vs. minimum feature size.

In the world of 3D printing, no factor influences print quality more than XY resolution. Often discussed but seldom understood, XY resolution (also called horizontal resolution) is the smallest movement that a printer’s laser or extruder can make within a single layer. The lower the number, the better the details. Yet this number is not always included in spec sheets, and when it is, the published value is not always accurate. To truly know a printer’s XY resolution, it’s important to understand the science behind the number.

Practically, how does XY resolution affect your 3D prints? In order to find out, we decided to test the Form 2 SLA 3D printer. The Form 2 has a laser spot size of 140 microns (FWHM), which should allow it to print fine details on the XY plane. We put it to the test to see if this ideal resolution holds true.

Designing a Test Model

XY Test Model
To test the Form 2’s minimum feature size on the XY plane, we designed a model (left) with lines ranging from 10 to 200 microns and printed it in Clear Resin (right).

First, we designed and printed a model to test the minimum feature size on the XY plane. The model is a rectangular block with lines of varying widths in horizontal, vertical, and diagonal directions to avoid directional bias. The line widths range from 10 to 200 microns in 10 micron steps and are 200 microns tall, which equates to two layers when printed at 100-micron Z resolution. The model was printed in Clear Resin, washed twice in an IPA bath, and post-cured for 30 minutes.

Analyzing the Model

XY Analysis
The model was photographed and tinted green to improve visibility. On the right side of the window, the vertical yellow line with black points measures the width of a photographed line.

After post-curing, we put the model under a microscope and took high-resolution photos for analysis. Using ImageJ, the NIH’s free image analysis software, we first scaled the pixels of the images and then measured the actual widths of the lines printed. We collected over 50 data points per line width to eliminate measuring errors and variability. In total, we printed and analyzed three models on two different printers.

Understanding the Results

XY Graph
The results indicate that the Form 2 has the same ideal and actual XY resolution for features that are 150 microns and larger.

As the print’s line width decreases from 200 to 150 microns, the ideal values are within the 95% confidence interval of the measured value. As the intended line widths get smaller than 150 microns, the measured interval starts to deviate significantly from the ideal. This means that the printer can reliably produce XY features as small as 150 microns, about the size of a human hair.

The Form 2’s minimum feature size on the XY plane is about 150 microns—only 10 microns larger than its 140-micron laser.

Based on our measurements, the Form 2’s minimum feature size on the XY plane is about 150 microns, which is only 10 microns larger than its 140-micron laser. The minimum feature size can never be smaller than the laser spot size, and there are many factors that affect this value: laser refraction, microscopic contaminants, resin chemistry, and much more. Considering the printer’s entire ecosystem, a 10-micron difference is nominal. Not every 3D printer’s published resolution holds true, so it’s a good idea to do plenty of research before choosing the one that's right for your project.

If your work calls for prints with intricate details, look for a printer with an XY resolution that’s backed by measurable data, not just a number.

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

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