Thanks for these helpful answers. I also found a great deal in the downloadable PDF files on this website written and illustrated by Jack A. Sobon called "Historic American Timber Joinery, a Graphic Guide." There is some interesting stuff about how tenons for the crucial tying beams (those in tension) were fashioned with dovetails and locked with wedges, to anticipate seasoning and shrinkage. One in particular called a 'kerf-wedged dovetail through mortise and tenon' in a building at the Hancock Shaker Village in Massachusettes has proven to be not up to the challenge. "Because of shrinkage of the height of the tenon, the wedges are loose, indicating the pins are carrying the load." Well I still like Shaker furniture even if their timber framing may not be an example to emulate.
