The video is now... obsolete. Here is a link to a much easier way to attach polycarbonate to the back of a cajon. https://www.cajonsmadein.com/blog/caj... I got frustrated with the clamp method and use this now. Works great. I'll keep the video up for historic perspective.

This video focuses on how I 'glue' and shape a sheet of lexan as a back for the Firebox cajons I build. But here I discuss the entire build process. The 0.093 inch thick polycarbonate (available at HomeD) gives these cajons huge bass and resonance. I use 3/4 inch cabinet plywood for the sides, top and bottom. A rough-cut cutsheet at 1:02 enables you to make 5 cajons from one 4'x8' sheet of plywood.

These boxes are not perfectly rectangular, the front slopes. There are 6 pieces to each box. The cutsheet does not include the front (tapa) or the back. The 4 pieces in the cutsheet I call the 'top' the 'bottom' and the 'sides'. The cutsheet results in pieces that are about 0.5 to 1 inch bigger than needed. This is so I can quickly rough cut them out of a single piece of plywood. I use cabinet grade plywood, so there is a 'nice' side and a 'rough' side. The cutsheet is designed to make the outside surfaces of the cajon from the 'nice' side. The capital 'R's and 'L's on the cutsheet indicate a Right side or a Left side piece. I rough cut the 4x8' plywood with a circular saw. The pieces that are 17x27 inches are further cut (the solid black lines) to 12.5x17x14.5x17" producing either two R or two L sides. The single 17x29.5 piece is cut to produce one R and one L.

Final trim can be done on a chop saw or table saw. After trimming, the top and bottom are ABOUT: top:12x12"; bottom:12x14.1". The sides are 'right trapezoids', about 12x16x14.1x16.3". The 'top' piece fits to the 12" portion of the 'side' and the 'bottom' piece fits to the 14.1" portion of the 'side'. 'ABOUT' because the front of the 'top' and the front of the 'bottom' must have slightly sloping faces (6.7 degrees) to match the overall angle of the front of the cajon. So these dimensions are approximate and will vary as you match pieces up. Important to label the inside and outside of all pieces prior to final trimming. If you confuse them as you are making final cuts you may have to re-cut other pieces to match.

Edges should be butt jointed with corner bracing, biscuit jointed or otherwise jointed to reinforce the joint. You could use 1/2 inch thickness, maybe less, for your sides so long as you add edging where you attach the polycarbonate and to the front to support the tapa. The polycarbonate needs to be screwed as well as 'glued' (2-part epoxy is best) so your edging needs to be thick enough to accommodate the screws.

The tapa is 1/8th inch thick (3mm) 'lauan' plywood. I have used lauan from recycled hollow doors and also from commercial suppliers of plywood. Lauan is sometimes sold as 'door skin' or 'underlayment'. Okoume marine plywood, 1/8th inch should also produce a very good sounding tapa. The best sounding cajons I have made are the ones I treated the tapa with Teak Oil. The sides, top and bottom are coated with a couple layers of brushed on Benwood Stay Clear polyurethane. Here are some links to Okoume/Lauan suppliers in the USA:
http://www.edensaw.com/mainsite/store...
http://boulterplywood.com/MarinePlywo...
https://www.menards.com/main/building...

At 11:41 there are three cajons with the bass port bar in place. The bar is just a scrap piece of 3/4 x 1.5 (2) inch plywood glued inside edge to inside edge. End-grain gluing is generally a no-no in woodworking but I use gorilla glue which expands into the end grain and seems to hold. I also drill a few small, shallow holes in each surface where the glue will go, haha, that's a hack but seems to work. Filled with gorilla glue they become pseudo-dowels when dry. The port is about 1 3/4 in high. To cut the port hole in the tapa 'back' the front of the tapa with a scrap of lauan to prevent the edge from fraying. Cut the port hole with a jig saw or chop saw and sand it perfect with a round sanding attachment on a drill.

See my other video on how to make the snare.

Nothing special about the whale tail port hole. Any shape will do. Be creative. But a big hole in one side is necessary, the bass port is NOT enough all by it self. I have one cajon with a bass port, a side port AND a big round hole in the bottom! It has awesome sound, if you want big bass, you have to let it out.