There is a router bit called a birds' beak????? That allows for a locking
M+T in each piece.. think floorboards in the round.....

See this for the idea......
http://www.rockler.com/how-to/specialized-router-bits-birds-mouth-multi-angl
e-bits-easy-bird-house-building/

Now all you need is a human powered router......

But truly, would this not be easier as a turning?  Glue it up in the
"square" turn it round....??????

Frank Filippone
Red735il@g...