To do this you will need some clamps and glue. After much trial and error I found that picture framing corner clamps do a great job of holding the four pieces together and they also act as a square and keep the cajon true . I have used wood glue in each of the router cuts and then clamped the sides together at the top. An adjustable band clamp is used to add even pressure to the bottom of the cajon and tighten up the joints. Next we need to glue in some blocks for reinforcement. We cut some blocks each measuring about 25cm long. The internal blocks are glued and then I rub the blocks into the corners of the cajon until the suction makes it difficult to move them. This is an old cabinet makers trick and achieves a very strong glue joint. Once all of the gluing is done we have to leave the cajon to dry. Overnight at least. When the glue is fully set and the clamps have been removed and your cajon body should look like this. In the next stage of building a cajon we will look at putting on the front playing surface and positioning the snare. But before that you could give the body of the cajon a light sanding and take off any excess glue . Also check that both the front and back rim of the cajon are smooth and even, this will ensure a good bond for the