Woodworker's Journal 1994-18-1, страница 16
Woodworking Basics -:—_ Bandsawn Bridle Joints A speedy alternative to the standard mortise-and-tenon by Roger Holmes 111 our age of technological miracles. I find it reassuring that ihe best method of assembling a wooden frame is still, for us as for the ancient Greeks, the mortise-and-tenon joint. From delicate picture f rames to massive post-and-beam buildings, assembled without glue, draw-bored and pinned, or bound by the latest concoction of ihe adhesive chemist, the mortise-and-tenon is slill unsurpassed for strength and longevity. Fond as I am of this paragon of folk engineering. 1 occasionally find myself willing to trade a bit of strength for something a lillle speedier to manufacture. The answer is frequently a bridle joint or, as ii is also called, an open-mortise joint, where ihe tenon slips into a slot open on three sides, rather than into a four-sided mortise (Fig. 11. Culling an open mortise wilh a hacksaw i>. much quicker than clearing the wasle from a standard mortise wilh an auger bit and chisels, or e\en wilh a drill-press-mounted hollow-chisel mortiser. Bui the joint can he cut fastest, both mortise and tenon, by employing a band saw. a method I'll describe in this article. Kase and speed in the making of this bridle joint comes at a price. Trapped tin all >ides by the mortise's encompassing walls, a "standard" mortise-and-tenon joint has considerable mechanical strength. It resists levering actions and. even when secured only by a wooden pin, it is almost impossible to pull apart. The bridle joim. on the other hand, has no mechanical advantage against'lev -ering. as the sketch shows (Fig. 11. Even when pinned, its strength depends heavily upon ihe glue bonding ihe cheeks of ihe tenon to those of the mortise. Fortunately, contemporary glues are up to the task, making the joint a viable option. In theory, you can substitute a bridle joint for any "enclosed" mortise-and-lenon al the corner of a frame. Several examples ihat I've used are shown in Fig. 2. 1 use another form of bridle joint less frequently, but it comes in handy for frames where a rail and stile form a "T", or for tables, w here an intermediate leg joins an apron rail, as show n in Fig. You'll notice that such joints have regained their mechanical advantage against levering or racking forces— shoulders of the "tenoned" member confine the edges of ihe skilled member. (You can also think of the joint as an "in-side-oui" morlise-and-lenon: the mortise has been halved, and each half moved to the outside face of the piece, separated by a bridge of wood. Likewise, the "tenon" is also halved, moved to the outside faces and separated by a slot.) As I've said, ihe main attraction of these joints i>- the ease and speed with which they can he cut. If you can make standard mortise and tenons, you'll have no trouble with bridle joints. The process I'll walk through here, using a band saw for much of the work. i-> particularly useful where several identical joints are Ifi TIk' Wood v. order's Journal |
