Monday, July 28, 2014
Frankly, Windows are a Pain by Jim Tolpin
Well now I know why windows are called panes...because they are truly a pain to make. Especially when you are challenging yourself as I am to do all the molding profiles, rabbets and joinery entirely with hand tools. (I’m not quite crazy enough to do all the stock sizing with rip saws and foreplanes).
Today I’m making the rail-to-stile joints for the big, 24-pane front window, which are franked (rather than haunched) through-wedged mortise and tenons. I was going to do my usual draw-bore pinned M&T, but a bit of research--especially in Charles H. Hayward’s book on joinery--convinced me otherwise. So I’m going down that road---and I have some theories about why this choice is typical of traditional sash joinery.
I’m pretty sure about the through tenon: With typical usage (sliding up and down in the case of double-hungs), strain on the pins would likely lead to enlarged holes and loose joints. Also, due to the sash’s exposure to the elements, the wood is going to undergo a lot of seasonal movement--again leading to loose pins. The through-tenons are much less subject to these symptoms of wood movement (no holes to enlarge for one thing). And unlike the pinned mortises---which eventually would have to be disassembled and re-bored--the wedged mortises could be tightened up by simply driving in (or possibly adding) the shims.