While designing a hole in\u00a0CAD<\/a>\u00a0software takes only a few clicks, mastering their\u00a0design for 3D printing<\/a>\u00a0can require some experience. For example, how should you design a vertical hole, which is perpendicular to your print bed, differently from a horizontal hole (parallel to your print bed)? What if the hole needs to be tapped?<\/p>\n From orientation to material shrinkage, hole design for 3D printing involves many intricate factors, resulting in noticeably different fits in your final prints.<\/p>\n In this guide, we\u2019ll break down our top tips for 3D printed holes. By the end, you\u2019ll have a host of tools with which to produce them for different uses.\u00a0Let\u2019s get started!<\/p>\n The first key to accurate holes is proper calibration of your 3D printer. Calibration comes in many flavors, so here are the top four that you should pay special attention to:<\/p>\n With these four steps taken care of, you\u2019re ready to start designing! Here are five tips to help you succeed at 3D printing holes.<\/p>\n 3D printers are quite capable of printing\u00a0bridges<\/a>, in the right circumstances. Bridges (shown above) allow plastic to be stretched from one end of a gap to another, leaving less opportunity for material to dangle in between. If you interrupt a bridge with holes, however, you ruin this delicate balance by preventing straight-line paths across the gap; the perimeters of the holes \u2013 circles \u2013 must be extruded into thin air, with nothing to stick to. This can create a disastrous mess of unsupported print paths, either ruining your print or causing a complete failure.<\/p>\n This issue is typically resolved in one of two ways:<\/p>\n First, some users like to break up mid-air holes such that they rest on a series of straight-line bridges. As you can see above, the perimeter of the hole is able to rest on a series of surrounding layers, preventing the aforementioned print-in-thin-air phenomenon. The result is a much cleaner and support-free product.<\/p>\n Alternatively, some users like to \u201cfill in\u201d their holes with one to two layers of plastic, essentially closing off their bottoms to create a flat bridge. By simply adding this thin layer, the holes are supported from below by nicely bridged struts, which can be cut out later with an\u00a0X-Acto blade<\/span>. From a design perspective, this is also much easier to implement than the previous option.<\/p>\n Shrinkage is another critical consideration for 3D printed holes. Despite the many ways that this can occur, the result is always the same: holes that are ever so slightly smaller than what you intended. While the change is subtle, it\u2019s enough to differentiate a bolt that fits too tightly from one that slips right through.<\/p>\n There are three main causes of shrinkage: material shrinkage, layer compression, and\u00a0mesh resolution<\/a>.<\/p>\n Material shrinkage is likely the cause that you\u2019re most familiar with: when a material cools down, it tends to contract. This is the culprit behind many infamous print failures, including\u00a0warping<\/a>\u00a0and\u00a0layer delamination<\/a>. For holes, this shrinkage will lead to slightly undersized parts that don\u2019t fit together properly.<\/p>\n Layer compression is another reason for shrunken holes, but it\u2019s actually caused by layers being oversized. When a printer lays down a new layer, it applies a compressive force (as visualized above). While this improves parts\u2019 strength, it also causes the lower layers to squish out slightly, extending beyond the boundaries that they were intended for. The result is a print that\u2019s too \u201cpuffed out\u201d in every direction, including within the holes.<\/p>\n Finally, there\u2019s mesh resolution. While not technically a form of \u201cshrinkage\u201d, mesh resolution does cause holes to come out smaller than originally intended. The key here is that, with most 3D printing files, \u201choles\u201d aren\u2019t actually perfectly round; they\u2019re\u00a0approximations comprised of polygons<\/a>\u00a0(as pictured below). The result is a tiny bit of corner-cutting, causing holes to turn out smaller than initially intended:<\/p>\n To fix these issues, you can start off by designing the holes to be a little too large, preempting the shrinkage. After printing, the holes will come out smaller, closer to the desired dimensions. It may take some trial and error before you hit the sweet spot, but you\u2019ll likely find some margin of inaccuracy that gives you the desired fit.<\/p>\n Alternatively, you can try the material shrinkage settings in your\u00a0slicer<\/a>. While different tools will have different names for this, there are typically options to specify your filament\u2019s shrinkage ratio. A similar setting is \u201chorizontal expansion\u201d, which again preempts the shrinkage by automatically expanding or contracting the model before printing.<\/p>\n Finally, you always have the option of leaving the holes as-is (or even slightly undersized). If you intend to tap threads, this gives you some meat for the screws to bite into; otherwise, you can simply drill the holes to the precise dimensions that you require.<\/p>\n So far, much of what we\u2019ve discussed applies to vertical holes. What if you\u2019re met with a horizontal one? In this case, your biggest enemy is likely going to be\u00a0overhangs<\/a>.<\/p>\n As you can see above, horizontal holes form overhangs that get steeper as the hole closes. When printing, this means that the tops of the holes will be prone to drooping, resulting in openings that are ever so slightly \u201csquished\u201d. If you\u2019re trying to fit a bolt through, this can be enough to block the opening.<\/p>\n Fortunately, this issue is easily combated by using teardrop-shaped holes instead of perfectly round ones (as shown above). This design avoids the harshest overhangs of the holes, allowing the prints to maintain the radii that you intended. While this technique may slightly increase the complexities of your 3D designs, it\u2019s a small price to pay for accurate final products.<\/p>\n In some cases, you may want a hole that wraps tightly around an object. This is often the case when you\u2019re mounting bearings or rods into 3D printed parts. How do you strike the balance between ease of assembly and a secure fit?<\/p>\n In these cases, your best bet may be to design holes that have a little bit of give. This allows for easier insertion of components, without sacrificing too much \u201cgrab\u201d and stability. Such designs typically come in two flavors:<\/p>\n So far, we\u2019ve focused on bare, clean holes, but that doesn\u2019t cover everything. From time to time, you may need threaded holes: these allow bolts to be screwed in directly, without separate tapping or nuts. While this can be quite convenient, it also renders many of the previous tips useless; it\u2019s difficult, for instance, to prevent shrinkage, as bolt threads have standardized dimensions.<\/p>\n To address this issue, we need to get creative with how we adjust the hole designs. One excellent tip is to use a push\/pull tool to widen the gap between a bolt and the threaded hole, effectively increasing the clearance. You can use this in conjunction with the aforementioned shrinkage settings to dial in the fit.<\/p>\n While designing, note that bigger threads will come out more cleanly, especially on\u00a0FDM<\/a>\u00a03D printers. We recommend printing with a lower\u00a0layer height<\/a>\u00a0to create more precise threads.<\/p>\nNail the Basics: Proper Calibration<\/h3>\n
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Tip #1: Don’t Start in Mid-Air<\/h3>\n
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Tip #2: Beware of Shrinkage<\/h3>\n
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Tip #3: Avoid Overhangs<\/h3>\n
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Tip #4: Add Tightening\/Compliant Mechanisms<\/h3>\n
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Tip #5: Tackle Threads<\/h3>\n
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