The trick to making these dove-tail joints is an emery board, the kind for filing your nails. The joints of the project box are laser cut with a "V" shape on one side and a smaller, rectangular hole on the other. The receiving rectangle cut is then sanded down to fit the V shape using the emery board. When assembled, the dove-tails hold the sides together tightly. Screws are added to hold the top and bottom in place, securing the enclosure. I used 4 (one for each corner,) but the box could easily be held together with just one.
The project that I'm making a case for is a modified Sparkfun single cell, lithium-polymer battery charger. The charger comes as a kit for charging li-po's at 100 or 500mA, but with a little bit of tweaking and a few components it can be made into a variable charger.
1/8th inch acrylic plastic. It will work with thicker plastic, you'll just need to do more sanding.
Machine Screws such as 1.25" Length 2-56 Thread from Ponolu
A project to put in the box
Emery Board. These can be found at drug stores and mini-marts.
Step 1: Designing the Joints
Design the enclosure with rectangular finger joints as per usual. This project was designed with 123D and then cut into slices using 123D Make for laser cutting. Another option would be to use the web based BoxMaker tool by Rahul Bhargava to automatically create a finger joint box design, and then use a vector editor (Illustrator, Inkscape, Corel) to add the dove-tails.
Based on the length of your machine screws, choose two opposing sides (top-bottom, left-right, back-front) and add 70 degree angles to the joints by making the outer edge wider. Here I've made all the tabs on the top and bottom into dove-tails and left everything else as it was.