Design for Printability

So you’ve got an idea that’s going to change your life, make you a millionaire and solve the world’s problems.  That’s great, but although 3D printing is pretty amazing, there are limitations and your design is key to getting good print quality.

The most common type of prosumer 3D printing is usually referred to as FDM – Fusion Deposition Modelling.  It’s really a description of the process, which involves successive very thin layers of plastic being deposited one on top of the other to build the model.  There’s a good explanation of it here.  FDM is (relatively) quick, cheap and effective, and print quality is increasing all the time as the technology rapidly evolves, but its weakness is in its very nature.



Consider a simple sphere.  There’s not really any simpler object, right?  It’s a single smooth surface, no complex details, no fancy designs, but spherical surfaces can be a nightmare for FDM printing.  The problem lies in the process of printing by layers.  A true sphere resting on a surface has only a tiny, tiny point of contact with that surface, so the very first layer put down in printing is equally tiny.  The next layer is larger so it has nothing to sit upon at the edge, so the very edge tends to sag down.  This happens on the next, and the next, and the next layers until the side of the sphere becomes more vertical and the “next” layer has something beneath it to print upon.  The upper surface of the sphere will print fine because the size of the layer is reducing and there’s always material beneath to print upon.  So, trying to print a sphere almost always ends up with a lovely top surface and a less than lovely lower half.

A sphere is, therefore, a good example of the biggest drawback with FDM, each new layer needs something beneath it to print successfully.  This drawback is not as big as it sounds as FDM can print some quite surprising overhangs, and it can “bridge” gaps quite well (for example, the upper part of a rectangular hole in the side of a box), but when designing your model, you should always try to create parts that avoid overhangs and allow for this drawback.  Sometimes the simple solution is to invert the model or print it on its side, and it’s possible to use “support material” (essentially “scaffolding” for the print that is extruded along with the main model), but sometimes it’s just a case of cutting the model into different sections.

So, when you’re designing your model, try to think not only about how it will work for your project but also how printable it’ll be.  The easier the model is to print, the more likely it is that your prints will be high quality and will be fit for purpose.

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