How Design and 3D Print Snap-Fit Joints for Enclosures, Boxes, Lids, and More

Snap-fit joints are so common in everyday products that many people may not even know that the features they’re constantly using are classified as snap-fit joints. This type of design feature is found in consumer products and industrial applications all around us — everything from food container lids, to seat-belts, and door latches — snap-fit joints are everywhere we look. 

As 3D printing has become more powerful and accessible, more people are now able to design their own functional prototypes or end-use parts, and need to learn how to create a high-quality, functional snap-fit joint. In the following guide, we’ll go through what defines a snap-fit joint, when and how they’re most useful, the design guidelines for a successful snap-fit, and the types of 3D printing technologies and materials for the best performance.

To see the step-by-step walkthrough for designing and 3D printing a snap-fit enclosure, watch our on-demand webinar here.

There are no exact dimensions that are ‘correct’ for any snap-fit joint — the optimal width, length, and shape of the different components of your snap-fit joint will change based on material type and overall size. However, there are some basic guidelines engineers follow when designing snap-fit joints, especially for 3D printing. 

1. A longer hook reduces stress on the base. 
2. A lower height reduces stress and the force necessary to assemble and disassemble the snap-fit joint. 
3. Width of the root does not effect tolerance of stress on the overall structure.
4. Taper your hook, or create a ‘trapezoidal’ elongated hook, rather than a straight/parallel/rectangular hook. 
5. Optimize for curves at the edges of your hook rather than fillets.
6. There is no perfect clearance for any assembly — some applications may require more force than others to remove the hook from the undercut, as a good thing, some may be designed specifically to disassemble easily. 
7. When in doubt, test and iterate!

For this project, we’re going to make a case for a Pine 64, a single board computer (download the .STL file on Pinshape to follow along). This tutorial uses Solidworks because of its popularity in product design and engineering, but you can use a similar CAD software.

First, use digital calipers or a ruler to measure your electronic component. We like to start enclosure designs by accurately reverse-engineering the PCB, measuring the board size, the location of mounting holes, and any ports or plugs that will need to be accessed through the enclosure. You might want to simply measure the overall maximum dimensions as a box, but it’s essential to know exactly where the main features are so that you can accommodate them. In Solidworks, reproduce these measurements as a grouping of basic boxes in a single part file.

When printing snap-fit parts like this case with SLA 3D printers, you have more than enough dimensional tolerancing to create the small holes and features the design requires. If you’re unsure about your part, consult the design guide, like this Form 4 Design Guide for Formlabs’ SLA 3D printer and this Fuse Series Design Guide for the Formlabs Fuse Series. 

Print orientation affects not only part quality and printability, but it can also affect mechanical properties, post-processing time on support removal, and print time. SLA snap-fit joint components should be oriented at a slight angle to the build platform to lessen the peel forces that might cause print deformation or lower accuracy. SLS snap-fit joint components are self supported, but for certain materials, like Nylon 11 CF Powder, should be oriented so the direction of strain is parallel to the top of the build chamber, so that the carbon fibers are rolled in that direction and overall strength is maximized. 

Design your snap-fit joint enclosure as an asembly, with each half of the enclosure modeled as a separate part. Consider the following:

1. How much of a tolerance to have between the perimeter of the PCB and the enclosure. Both Formlabs SLA and SLS 3D printers can easily achieve a 0.4 mm tolerance, while FDM 3D printed parts may warp slightly, and a more conservative tolerance closer to 1.5 mm to 2.0 mm may be best. 

2. Cut away port openings — considering the spatial need for cable material around the port opening as well as the port itself. An extra 2.0 mm all the way around the port opening is a good starting point. 

3. Choose whether to create a larger bottom half of the enclosure where all ports fit inside, or one like the above image, where some ports stick up a bit. Here we’ve made a shallower bottom half so that the cables only have to reach a short ways inside, and rely on the top half to cover the rest of the protuding ports. 

The top enclosure has the same treatment of the cut details to accommodate the taller ports and additional material to close off gaps in the bottom enclosure. The sunken portion in the middle is optional, but adds a slightly more organic and interesting visual detail. 

You could use any of the types of snap-fit joints we talked about earlier, but here we opted for the most basic — and internal cantilever snap-fit joint that offers strength with minimal material usage. The snap-fit design is the same on both sides of the enclosure. To enhance the strength of the snap-fit joint, you can extend the protrusion so that it requires more force to remove it from the cavity.  

In this snap-fit assembly, it’s only 1.2 mm, but 2 mm or more would make the snap-fit enclosure much more tightly secured — there is no right answer, it just depends on your ideal use-case and how easily you’d like to diassemble the enclosure. 

In this particular design, the pins on the PCB take up quite a bit of room, so the snap-fit ‘lock’ is able to just squeeze in, while still providing enough force to hold the enclosure together. The cantilever joint is extruded 20 mm long, which increases strength.

Above you can see a sectioned exploded view of the snap details on the enclosure, along with the PCB showing the location of the pins (in black), which limit the size of the cantilever joint. Alternatively, instead of the snap cavity hiding inside of the bottom enclosure, you could cut this detail through to the outside, allowing your snap-fit joints to be longer.

Lugs are small extrusions that slide within the opposite enclosure to secure the two halves. Add lugs to your design to keep the two halves from sliding. Lugs are small extrusions that insert into the opposite enclosure. Because we created two snap-fit joints on opposite sides, you might need these on just the two blank sides. For this larger case, we put them in each corner. The material extrudes only 3 mm down, but this is enough to prevent movement on 3D printed interlocking parts.

Though adding extra details beyond the functionality of the snap-fit joint aren’t necessary, they can elevate your design without too much added effort. Once your part is finalized in your 3D design software, export it to PreForm, and choose your printing technology and material. 

PreForm, Formlabs’ print preparation software for both SLA and SLS technologies, has many features built in, like adding texturing, extruding product names or labeling for iterative efforts, and more. Once you’re set up your print (either manually or using PreForm’s automated print preparation tools like auto-generated supports for SLA or auto-generated packing for SLS), you can add additional details, or make edits to the orientation and support structures. 

Once your part is ready to be printed, send it to the Form Series or Fuse Series printers through PreForm. When the print is done, post-process it by removing supports and washing and curing the parts (SLA) or removing powder, media blasting and polishing (SLS). Additional, advanced post-processing techniques like coating, plating, vapor smoothing, and dyeing are possible, and can make your parts look more like end-use consumer products. Certain processes, like coating, may affect tolerances and the function of snap-fit joints, so consider these in your original designs. 

3D printing offers a range of benefits for the fabrication of snap-fit joint parts like enclosures, boxes, lids, and functional assemblies. The ability of advanced 3D printers and materials to create complex, organic shapes that have tight tolerances, fine features, and smooth surface finishes make it an ideal technology for fabricating these parts. 3D printed materials have become more industrial and durable, making long-term use of snap-fit joints possible, even with repeated usage. 

To learn more about the different 3D printing materials available, visit our materials library or request a sample.