Step 1: Prepare Files for CNC
I designed the stools in Rhino, but could have used a 2D Vector program such as Illustrator.
Step 2: Measure and CNC
The design uses 3/4" (18mm) Baltic birch plywood, it's important to measure the actual thickness of your plywood and adjust the width of the joints in the files. The goal is to achieve a friction fit. This way you can always disassemble them later for easy transportation. I would recommend first cutting two test slots to see how they fit together.
I used a ShopBot and a 1/4" spiral down cut cutter and sanded the finished pieces. I selected T-Bone Fillets for the inside corners.
Step 3: Assembly
Use a mallet and a piece of sacrificial board to hammer together the legs, then the seat. Stain or oil as desired.