A couple months back someone soldered up an audio amplifier kit to use with the Raspberry Pi jukebox. It’s been working well with some old speakers but it’s open to the elements and is powered by the variable bench power supply. Since I was always nervous I would fry the thing each time I used it, I decided to design up an enclosure for it.
I used Onshape to do all the design work. It’s a free (as in beer) cloud based CAD program.
The first step was to take measurements of the amplifier. I disconnected all the wires and used some calipers. Most of the measurements were rounded to 1mm though some were down to 0.5mm. I wanted to keep the enclosure small, both as challenge to myself and to reduce the amount of material required (6mm plywood in this case). I found a power brick in the free box that should power the amp fine and designed the power inlet around its cable. Following in the advice of Ben Heck, I decided against using a simple hole for the power cable since it would trap the amp and enclosure together. I went with a notch on the edge of the back so that when the lid is removed the cable is free once again.
The design went fairly smoothly, the “teeth” that form the edges of the box were laid out manually. One of these days I’ll write a script of some sort to do it for me.
The entire CAD project is available here (no account required!).
One problem I ran into is that the DXF files Onshape exports don’t always include all the geometry. From what I can tell It’s only ever circles that it fails to include. The workaround I came up was to create a copy in LaserCut 5.3, mirror the copy then unite lines. This relies on the pieces being symmetric about at least one of the axes. The DWG files exported don’t have this issue but when I converted them to DXF those also had missing geometry. It could simply be an issue with the DXF format itself.
The puzzle piece style method to fasten the edges requires tight tolerances. Right now the positive and negative “teeth” are the same width and the kerf of the laser is enough to allow them to fit easily together. Once glued, however, the joint doesn’t seem as strong as it could be. I’d like to try adding some negative length to the negative tooth thereby snugging up the joint.
I included a buffer in the dimensions where I thought I might run into troubles. This seemed to work well except for around the perimeter of the PCB. I may have been too fast and loose with my measuring but now the PCB fits very tightly into the enclosure.