I have an outdoor chair...not sure of the type of wood. My guess is cypress. One arm was secured to the piece below it with mortise and tenon joinery. That broke with loss of a a good portion of the tenon. I think the tenon was undersized. My thought is to rout out both sides and use a floating hardwood tenon, a little larger and perhaps a tad longer. My difficulty in the past with doing such a technique has been to accurately mark both sides so the mortises line up. I seem to have difficulty with the system I used, thus this plea to the experts on how to accomplish that with good accuracy. Any advice here will be greatly appreciated. Thanks in advance. Don M