Ultimaker XY Axis Square

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The key to making these effective is for them to be identical in length. I prefer to print one at a time, back to back, with identical settings for temperature, flow, fan speed, etc. The part tapers at the top and bottom to ensure that the contact areas are mid-print when things have settled down. I think 0.2mm layers work well, and 30% infill was enough for me. Print with a filament that extrudes well in your machine, and go fairly slow for accuracy. I added a small flat in the "V" end to allow measuring the length of the arm with calipers. I also usually take a utility blade to each end, scraping (not cutting) lightly across the contact surfaces to knock down any outlier layers and bring them more in line with each other. You want very repeatable, even layers for this part to be helpful. My arms measure within 0.02mm of one another in length. You can make things much easier on yourself by loosening your belt tension and aligning the set screw(s) on the pulleys of the axis you are working on, so that they are easily accessible.