BETA - 3D Printing Knowledge Base

How to design for 3D printing, from quick adjustments to 3DP-oriented design.

It can be frustrating to attempt a 3D print for the first time after hearing about its capabilities, only to see your part perform differently than expected or fail entirely. Much like any other manufacturing process, 3D printing has a variety of strengths and weaknesses. A few design tweaks can easily turn a failed print into one that taps into the strengths of 3D printing: strength, few geometrical limitations, quick turnaround, and inexpensive production. On the other hand, designing your parts for 3D printing from the start can produce extremely efficient parts.

Printing assemblies

When designing 3D printed parts for assembly, there are a few key considerations to keep in mind. Typically, you shouldn't design load-bearing threads into a 3D print. Any holes desired in the final part need to be modeled in; you cannot drill new holes in a 3D print due to the internal lattice.

Interfaces need to be designed for 3D printing. Threaded inserts are a great way to include threads in a part quickly and cheaply. You can also include machine nuts in a part by designing slots for them into the part itself. Clips, friction fits, slider joints, magnets embedded in the print, latches, living hinges, and more are all possible with the proper design.

Print orientation matters

3D printing is a layer-based process, which means that parts exhibit anisotropic strength and flexibility. In short, the way the part is laid out on the 3D printer has huge effects on how the part will perform. Typically the weakest section of any print is the lamination between layers. As a shear or tensile force is exerted on the print, the part is most likely to fail by delaminating.

If your part is load-bearing, consider how the load is applied to the part. If it produces significant stress "against the grain," it may need to be reoriented.

Tolerances

3D printed parts can interface excellently with other prints or existing objects, provided the parts have been designed with the correct mating tolerances. Deciding what type of fit you'd like, there are a range of allowable tolerances--clearance (>0.50mm), transition (0.30 - 0.20mm), or interference (0.20 - 0.10mm). It is often worthwhile to first print a tolerance gauge to understand the specific tolerances allowed by your printer.

Internal Geometry

One major feature of 3D printing is the capability for internal geometry. Parts can be printed with variably dense insides, using a lattice structure printed inside the part called infill. This is typically generated by the slicer, the program which converts a 3D model into executable code to be 3D printed.

Other internal geometry can be introduced using the model itself. Free-floating parts can be printed seamlessly inside of other parts. Print-in-place assemblies are assemblies with articulating parts printed in a single pass, pre-assembled and ready to use straight off the print bed.

Designing with Fillets and Chamfers

Fillets and chamfers are useful tools in preventing stress intensities in your final print. If your part has sharp bends and angles, the print will likely crack along these areas. Fillets can help relieve stress from these areas, and can reduce the artifacts associated with abrupt changes in print head motion. Chamfers are excellent for reducing thermal artifacts from the area where the print contacts the bed or raft of the print.

Consider using these features to improve the final look, feel, and strength of your printed part.

Understanding Overhangs & Bridges

Because of the layer-based method of 3D printing, layers need support from beneath to resist drooping or failing completely. The effects of overhangs depends largely on the layer height, but as a general rule of thumb, overhangs beyond 50 degrees from the build plate should be avoided to maintain quality. For overhangs beyond this threshold, support material is typically required.

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