Since the main ingredient in a Cajon is half a snare drum snare it’s only good fiscal policy to make two. Otherwise what would you do with the other half-a-snare. And I have two kids, so that works out
I measured a chair seat at 18 inches tall, so I made my cajons 18 inches tall. And 15 inches square on the top and bottom. I cut my tops and sides out of some spare 3⁄4 inch 13 ply baltic birch plywood. I ran out of the Baltic Birch so I cut the bottoms out of some lesser plywood. It’s the bottom so it won’t show.
Apparently I failed to take the blade width into account, though I thought I was careful, and all my boards ended up an eighth of an inch short. This turned out to be a good thing as the only 1⁄8 inch plywood I could find for the front was 24×30. I can easily get two fronts at 177⁄8 x 147⁄8 out of that. More difficult if they had to be 15 inches wide.
I put a 3⁄8 inch deep, 3⁄4 inch wide, rabbet in the side of the tops and bottoms to glue the sides to. So my finished height will be more like 183⁄4 or 185⁄8. I’m not comfortable relying just on the glue for that joint, since there is likely to be a lot of racking, so I may screw or peg those. A lot of people use a block on the inside to reinforce that joint, I may do that as well.
My son requested that his cajon be just finished wood. My daughter wanted something more complicated. Once my son saw what my daughter’s was going to look like decided he wanted something more complicated too. Consequently using wood stain with stencils is a separate blog post located here.
A dry fit revealed my sides were 1/2 inch too long, or my front and back were 1/2 inch too short. Either way I trimmed the sides rather than elongating the front and back. My wife tells me I should get a refund from St Olaf where I got my undergrad degree majoring in math. I tell her that’s mathematics, not arithmetic. I’m an expert in spherical trigonometry, but sometime addition eludes me.
The top and bottom were 1/4 too wide, but I did that on purpose (no, really, I wanted to be absolutely sure the rabbet was deep enough). This meant I needed cauls to bring the sides into the rabbets. The glue up looked like this.
Picture of glue up
I decided to add a few screws to re-enforce the joint. I drilled pilot holes but the plywood split anyway. Thankfully that won’t show. Lessons learned – maybe the screws aren’t necessary.
picture of split
I thought about adding reinforcement on the inside of every edge, but after glue up it seemed pretty solid even without the back attached. Since I had some rough 2×2 scrap I cut one of those to length and reinforced the bottom at the back. This’ll make it slightly bottom heavy and satisfy my apparent need to overbuild everything.
picture of reinforcement
The sound comes from the back. The back is 1⁄2 plywood and needs some holes for the sound to come out. Most people seem to make that about 3 inches in diameter. I saw one I liked with a series of holes in different diameters so I tried that on mine.
picture of back