Making Tomu: Plastic Case Overview

This series of blogposts details the steps I took to create a plastic case for Tomu.

Tomu is a project I helped to crowdfund. Initially created by Tim "mithro" Ansell, Tomu is a tiny computer that fits entirely inside a Type-A USB port -- the sort usually found on a PC or laptop. Initial designs for Tomu used a variety of methods to mechanically seat the circuit board inside the computer, ranging from 3D printed shims to slightly oversized PCBs to just folding over a business card and jamming it in the slot. They all worked to varying degrees, but all left something to be desired, and none were really beginner-friendly.

One of the stretch goals for the crowdfunding project was to design and produce a plastic case in order to make Tomu more accessible. By designing a custom case, we could ensure that Tomu fit snugly into a USB port without any misalignment or shorting out against the case. Additionally, a custom case could make it easier to remove Tomu without the need for tweezers, and lets Tomu work for people who don't have access to a 3D printer.

We met the stretch goal fairly early in the campaign, which meant I actually had to learn how to design a case and get it manufactured. This series of blogposts will detail the steps I took to produce a fully functional case, from PCB design to finished product. I am very happy with how the result turned out, and would definitely recommend this approach for anyone looking to work with plastics. We were fortunate in that Tomu itself is small and has no moving parts, nor did it require any sliders to create complicated forms in the mold. The steps taken here are applicable regardless of the complexity of your project.

Each of the three posts is targeted at a different step of the process, and may be interesting to different people for different reasons.

  1. Modifications made to the PCB to make it compatible with the case. The Tomu PCB is designed in KiCad, and underwent two revisions prior to shipping. This article discusses the considerations that were made when planning the final case design.
  2. Designing the case in FreeCAD. Much of this article details the basics of how to design a part in 3D in FreeCAD, as well as how to import KiCad projects for reference.
  3. Communicating with the factory. It is important to realize that humans will ultimately craft your product, and so communication is paramount. This article discusses file formats for interchange with the factory, checking their work, helping them to check your work, and ultimately creating a finished product.
Making Tomu: Plastic Case Overview
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