This design is an existing product that is sold for 200 Euros. I worked with it for one day and loved the simplicity of the design and wanted one for myself.
The wood is the second half of one sheet of plywood that I bought for another project.
I spent a lot of time on making the template. First challenge was calculating the correct difference between slot in the template vs. result I wanted for the router. Second was using the table saw correctly to get the exact size I wanted.
Woods: spruce plywood