I would first have to agree with buying t&g instead. I've done quite a few stalls and will use 2x8's instead of 2x6, it just makes a better stall.
But I am going to assume you already have the stock and that isn't an option.
Due to bowed, imperfect boards i would do it by hand with a heavy router 1/2" collet with a rabbet bit, this way it will follow the board and it is easier to handle the router than handle the board.
Another option to consider that I have done is peg it every 3'. Get some 3/8" round bar (I used a galvanized spike) cut it into at least 2" pieces. Make up a 1x2 to lay on the board edge to drill your holes.
This did very nicely on our stalls.
I had some short lengths to use up so I cut them to 7' and 3', alternated them back and forth using the pegs and it's as rigid as the full length boards.
But I am going to assume you already have the stock and that isn't an option.
Due to bowed, imperfect boards i would do it by hand with a heavy router 1/2" collet with a rabbet bit, this way it will follow the board and it is easier to handle the router than handle the board.
Another option to consider that I have done is peg it every 3'. Get some 3/8" round bar (I used a galvanized spike) cut it into at least 2" pieces. Make up a 1x2 to lay on the board edge to drill your holes.
This did very nicely on our stalls.
I had some short lengths to use up so I cut them to 7' and 3', alternated them back and forth using the pegs and it's as rigid as the full length boards.
