There is no faster way to go from solid CAD model to physical part than 3D printing. 3D printing also allows the designer (thats you!) to break many of the rules that apply to subtractive manufacturing techniques like CNC machining. With these powers combined…3D printing is awesome!
That said, 3d printers, like any manufacturing technique, have limitations. Inexpensive machines (<$3000) are generally all Fused Filament Fabrication (FFF) types, so that’s what we’ll focus on for now. These machines construct 3-dimensional parts by building them layer-by-layer with extruded plastic. Generally these printers print one layer at a time on a fixed X-Y plane. After one layer is complete, the build platform moves down by one layer thickness (or the print head moves up), and another layer is deposited.
Here are the design ‘rules’ that I use when I design in CAD for FFF printing. Keep in mind, rules are only guidelines; please stretch and break these as much as you can to learn about your machine and its capabilities.
- Design your part to have a flat surface. While it’s not critical, it’s very helpful to have a nice flat surface to select as your first layer. You can have your slicer fake it with support material, but support material is a pain to clean off and can mess up your beautiful layered surface finish.
- Keep under-hanging angles at or below 45°. If you keep your underhangs at or below 45°, you won’t need support material! They’ll all come out looking very nice and you’re more likely to have successful prints on the first try.
- Keep bridges to about 10mm. Bridging–the act of trailing filament between two supports (forming a bridge)–is fun. As long as you keep them short, it’s easy, too. If you’re planning a bridge on a large part, try to test it out first to make sure your part won’t fail. Nothing’s worse than having a print fail towards the end of a large part! EDIT: I just bridged 60mm. It took a couple layers to firm up but I was blown away that it worked as well as it did. It just goes to show…BEND THE RULES!
- Design your own support material. You can minimize the supports needed and the effort required to remove them by designing them yourself. Obey rules 2 and 3 and keep the supports small enough to easily trim with a pair of snips.
- Use the X-Y gantry for complex geometry. The X-Y gantry moves with very good resolution. The Z: not so much. I think the topographic look formed by the layers of material is really cool, but if you have complex geometry that you want to come out just right, try to use the X-Y gantry as much as possible. Common examples include holes, text, and logos.
- Load along the layers. If you are designing a part that sees some load, design it in such a way that the loading does not try to pull apart the layers. Any applied forces and bending should be along the layers. Think about it like this: if you only printed half of your part, do you still have the necessary geometry to support your loading scheme?
Now get out there and make stuff. Keep these rules in mind, but be sure to stretch them!