Part Interfaces

A crucial consideration for any design is how it connects to surrounding parts in an assembly. With 3D printing, your options for part interfaces are wildly diverse, thanks to the geometric complexity the technology allows for no additional cost. In this guide, we've compiled some common ways to create part interfaces with 3D printing. Note that this cannot possibly be a comprehensive list; the list of possible configurations for interfaces is infinite. However, there are some common methods which can be adapted and built upon to perfectly complement your design.

Holes

Never drill holes into 3D printed parts during post-processing. Model them in to the part, and not just by using hole callouts; these have to actually be a part of the mesh. The reason why is because 3D prints are typically semi-hollow, and drilling into the part will not yield a strong hole as a modeled one would. As a part of prototyping, drilling holes can be a great way to quickly test new features without starting a new print, but you should never rely on them for your final print.

Holes are discussed at greater length in our page on tolerances, where we discuss how to design for different types of fit.

In this specific example, the M5 threaded inserts cost $18 for 40 fittings. For less than 50¢ apiece, these inserts have turned a cheap 3D printed plastic part (<40¢ of plastic) into one that has lasted multiple years of use on a 3D printer. This is an excellent example of an end-use part, quickly and cheaply printed for less than $5 total.

We recommend finding the measurements of the threaded insert and running a few test prints. For this particular print, the outer diameter was measured as 6.50mm, so I ran a test print with a few holes of different diameters. I then added an insert to each hole, and used a machine screw to manually test the pull strength of the insert. The best result came out at 6.80mm diameter. We recommend performing the same test before committing to a larger print. For more information on inserts, Stefan of CNC Kitchen did an excellent analysis on his blog.

Nuts

Using machine screws and nuts are a great way to hold your parts together. This is by far my most frequently used method, as it is cheap, robust, and doesn't require you to throw away the hardware in case the print needs a redesign. It also is incredibly quick and easy to implement: just design a slot where the nut can be added to the part. You're done--easy, robust, removable hardware added to a 3D print!

Zip Ties

Zip ties are super cheap, and ridiculously simple to design for. They can range from simple cable management for electronics enclosures to hardware for final products--seriously. When used properly, they can be an excellent low- to mid-strength fastener for a wide range of applications. Simply cut a groove into the interior of the part as shown.