Fig. 593.
The mortise and tenon given above is a very simple form. Sometimes the tenon is short and does not go through (Fig. 593). This is a common form, and is used a great deal in the best work. It is sometimes called blind mortising, the tenon being known as a "stub" tenon.
Mortise and tenon joints are sometimes merely fitted together, but can also be glued (see Gluing), pinned, wedged, or dovetailed and fastened with a key.
To pin a mortise and tenon, simply mark a point with square and gauge upon each side of the piece containing the mortise (Fig. 593), fit the tenon in place, and bore in from each side (or in rough work bore right through from one side until the spur appears on the opposite surface) (see Boring). Then drive through a snugly fitting pin and trim off the projecting ends. The pin should be slightly pointed before driving, on the same principle that the end of the tenon is bevelled. It is not necessary to round the pin. An eight-sided one is just as good.
Do not use too large pins. In ship-building, bridge-building, and old-fashioned house-framing pins and treenails from 1" to 1¾" or more in diameter, are used. Dowels of various sizes will usually answer for such framing as you may have to do (though a rift-pin is stronger). For such work as pinning a joint in a chair, you will not need anything larger than a ¼" hardwood pin.
You must use judgment as to how near the edge to place the pin. If you put it too far from the edge, its hold on the tenon will be weak and the end of the tenon may break out (shear). If you put it too near the edge, the sides of the mortise may tear or split out.
Fig. 594.
Sometimes, particularly in timber work, to insure a snug fit at the joint, "draw-boring" is resorted to (Fig. 594). The hole for the pin is not bored through the tenon as just shown, but is bored a trifle nearer the shoulder of the tenon than the other holes (in the mortise-piece). The result is that when the pin is driven through it draws the tenon-piece down to a snug fit at the shoulder. But this has to be done with judgment. If the hole in the tenon is too much out of line, driving the pin through tends to split (strictly speaking to shear) the end of the tenon, and too much strain is put on the pin.