The bottom of the 2 main sections is 17 cm and the odd angle of the bottom cut out is due to the compound angle caused when the two sections are opened. it is 20 degrees to the base
I sprayed the whole thing with some left over black paint for the final effect.
If you put 2 pieces of board together for the cutting out they will match exactly.
This was made for a roprano but it could be upscaled for any other Uke'