The first thing we'll need to do is design our case. I like to model the electronic components first, so that I can design around them. In this project, we just need to make the Joy Bonnet and Raspberry Pi Zero. These two boards are held together with headers, so they're essentially secured by friction. We can use this to our advantage and avoid having to use screws to secure two halves of the case together. We'll design the case in two halves, one for the Joy Bonnet, and the other for the Raspberry Pi. As long as each component is secured to a halve, we can easily join the two together.
I do most of my work in Autodesk Fusion 360. It's a free 3D modeling program thats great for making parametric models and has integrated CAM. I put together a video that walks through designing the Adafruit Joy Bonnet step by step. This is a multi-part series that goes from making the components, to making the two halves of the case and the buttons. I've also made the components and case design a free download, so you can go ahead and start machining the case. It's very software specific, so we won't cover all the details in this written guide.
Because we're going to CNC mill the design, we need to think about design for manufacturing. In our case, we're cutting the design out of a block of wood. There's certain limitations that we have to keep in mind, such as avoiding undercuts and overhangs. If you think about how the CNC machine cuts from the top down, we can't easily make cutouts with overhangs. This means, if we need an opening, it needs to start from the top.
We need to have cutouts on the side of the case for the two microUSB ports, miniHDMI, camera connector, and SD card. These cuts only need to be made in the bottom half of the case.
On the top half of the case, we need cutouts for the buttons and the thumb joystick. These cuts will be on the very bottom of the case.
The two boards feature four mounting holes. One on each corner. To secure the boards to the two halves, we'll make standoffs to elevate the PCBs from the surface of the case. These standoffs will have holes in the center and have to line up perfectly with the mounting holes in the PCBs.
Important thing to consider is the build volume of our CNC machine. The Othermill Pro has a work area of 5.5 × 4.5 × 1.35 in (140 × 114 × 34.3 mm). Our case design should fit on our spoilboard.