How to allow for expansion & contraction in a wide door rail?
I am building a full-light exterior door, with a triple-glazed window unit. I’d like this door to last hundreds of years, so I’ve bought some quarter-sawn 8/4 white oak, and I’m planning on a 12″ bottom rail to take the weight of the glass.
My plan is to give the bottom rail a double tenon, 3-1/2″ per tenon, with a full haunch, and pin both tenons. Single pinned tenon on the top rail.
What’s got me worried is thinking about expansion and contraction of the bottom rail, and how to allow for it in the joints. I’m thinking that perhaps I could just pin one of the double tenons and leave the other one floating. Or perhaps I could relieve the base of one tenon to allow for some movement. Is there a better way, or am I overthinking it?
What did the old-timers do? I haven’t been able to dig up anything on the subject, and it seems that it’s been almost unheard of to use such a wide rail for quite some time.