Another teacher and I at my school have been working on musical instrument design. We were originally going to make a djembe by carving it out of a log in a traditional way, but we decided to give a laser cut method a try first. Circles were cut out of 1/8" thick, baltic birch plywood. The circles were 5 mm thick. The diameter of the circles varied in increments of 1/20" so there are 10 different sets of concentric circles. Two full sets of these circles were cut out to allow the taper of the top and bottom of the drum to be gradual or steep. Goat skin heads were used for the drum. Make sure if you build one these drum that the goat skin head is substantially larger than the drum diameter so it can be fed through the rings. We used an 18" diameter head on the 10" diameter drum and didn't have too much extra. There are some nice videos online showing how to replace the drum head on a djembe which will help with the stringing of the drum loops, etc. We built a small (6"? diameter) and larger (10" diameter) drum and intend to build a larger drum in the future.
The pictures here show the two drums we made along with a professionally made talking drum we used to compare the tone of our drums to a "real" drum.
I have been building a much larger djembe (the top ring is as large as the laser cutter can cut - 2 feet across). I used thicker plywood for the top of the drum - 1/4" thick luan.
Step 1: Cut Rings
Cut out the rings as described in the previous step. The Inkscape file we used for the 10" drum is provided. You will also need two rings with an inner diameter slightly smaller than the final diameter of the drum head to serve as the rings for mounting the drum head.
Step 2: Stack Rings and Glue
Stack up the rings to get the shape you want. We found a gradually tapered bottom and a rapid and then gradually tapered top worked well. We hope to play with different shapes for the "bowl" of the drum in the future to see how it changes the tone of the drum. Try to keep the rings in order when you take them off the laser cutter since getting them back in order takes a little effort. If you hold the rings against the table on one edge side by side you can sort them by size. We used normal old school glue to glue them together. The glue sets pretty quickly so make sure things are lined up as you go.
Step 3: Wax Edge and Add Drum Head
The top edge of the drum should be waxed to allow the drum head to slide over it more easily as it is being tightened. We also used a small sander to round off the corners slightly to protect the goat skin head from getting torn. For the wax we used wax left over from doing the SeaPerch competition where motors are surrounded with the wax used to seat toilets. This wax is very soft and easy to spread around the lip of the drum.
To create the rings for the drum head mounting we used plywood circles covered with duct tape. The inner diameter of this ring is slightly less than the outer diameter of the top ring of the drum. If you are clever you can create these rings as you cut out the concentric circles for the drum. We wasted a little wood and cut them out after the fact since we hadn't planned ahead for this step. The top ring must have string tied around it. There are a few great videos online that show how to do this (look for videos about replacing the drum head on a djembe). We used basic string for this. A second loop of string is placed further down on the drum in the narrow section which is used to help create tension along with the top ring to tighten and tune the drum head. This was created using the same string but multiple length of it were wound around itself to make it stronger.
Make sure you soak the goatskin head long enough for it to get it soft. Once it is ready place it flat on a table and rest the drum top-side down on it. The drum head is then pulled between both rings and the drum body before being wrapped around the bottom ring and back under the top ring (top and bottom refer to the orientation once the drum is back upright). This step is the hardest part of making the drum and why it is essential to have a large enough drum head to have a little extra (but not too much extra) to work with. Needle nose pliers are helpful for pulling the drum head underneath the top ring on the return part. Be careful not to rip the head. I will try to post video of this process soon once I have a chance to edit the video down a little.
Once the head had been place under the top ring, it is time to tighten the drum head. Traditionally this is done with rope, but my first attempt at this did not give me the tension I needed to get a good tone so I switched to zipties which worked much better. Make sure you place the zipties through the top rope and bottom rope loop. It is a good idea to put them all in place before tightening them since it gets much harder to get them under the rope once you start tightening the zipties. Also try to alternate to different sides of the drum as you tighten them to put even pressure on the rings and make multiple passes around the drum to tighten it a little more each time. This method does not make it easy to carefully tune the drum, but it does get the drum head tight enough to give a nice sound.
Once you get the drum head tight enough, play away. So far our drums have held up to playing. The larger drum has a nicer sound which is why we hope to build a substantially larger drum soon.