This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
In a consideration of bearing joints for beams, the term "beam" is taken to include all pieces which carry or receive a load across the grain. The simplest of these is the halving joint, shown at Fig. 470, where 2 pieces of cross bracing are halved together. This joint is also shown at Fig. 471, where the ends of 2 wall plates meet each other. When a joint occurs in the length of a beam, as at Fig. 472, it is generally called a scarf. In each of these examples it will be seen that half the thickness of each piece is cut away so as to make the joint flush top and bottom. Sometimes the outer end of the upper piece is made thicker, forming a bevelled joint and acting as a dovetail when loaded on top. This is shown at Figs. 473 and 474. When a beam crosses another at right angles, and is cut on the lower side to fit upon it, the joint is known as single-notching, shown in Fig. 475. When both are cut, as in Fig. 476, it is known as double-notching. These forms occur in bridging and ceiling joists. When a cog or solid projecting portion is cut in the lower piece at the middle of the joint it is known as cogging or caulking, and is shown in Fig. 477. Figs. 478 and 479 show two forms of the joint occurring between a tie-beam and wall plate in roofing.
Dovetailing is not much used in carpentry or house joinery, owing to the shrinkage of the wood loosening the joint: 2 wall plates are shown dovetailed together at Figs. 480 and 481; in the latter, a wedge is sometimes inserted on the straight side to enable the joint to be tightened up as the wood shrinks. Tredgold proposed the form shown in Fig. 482, which is known as the "Tredgold notch;" but this is never seen in practice. Tusk-tenoning is the method adopted for obtaining a bearing for a beam meeting another at right angles at the same level. Fig. 483 shows a trimmer supported on a trimming joist in this manner; this occurs round fireplaces, hoistways, and other openings through floors. Fig. 484 shows the same joint between a wood girder and binding joist; it is also used in double-framed flooring. The advantage of this form is that a good bearing is obtained without weakening the beam to any very great extent, as the principal portion of the material removed is taken from the neutral axis, leaving the remainder disposed somewhat after the form of a flanged girder. When a cross-piece of timber has to be framed in between 2 beams already fixed, a tenon and chase-mortice (Fig. 485) is one of the methods adopted.
If the space is very confined, the same kind of mortice is made in both beams, but in opposite directions; the cross-piece is then held obliquely and slid into place. Occasionally it is necessary to make the chase-mortice vertical; but this is not to be recommended, as the beam is much weakened by so doing - it is shown in Fig. 486. In some cases of ceiling joists a square fillet is nailed on the tenon and chase-mortice, to take the weight of the joists without cutting into the beam. While speaking of floors, the process of firring-up may be mentioned; this consists of laying thin pieces, or strips, of wood on the top of joists, or any surfaces, to bring them up to a level. Firring-pieces are also sometimes nailed underneath the large beams in framed floors, so that the under side may be level with the bottom of the ceiling joists, to give a bearing for the laths, and at the same time allow sufficient space for the plaster to form a key.
Brandering is formed by strips about 1 in. square, nailed to the under side of the ceiling joists at right angles to them; these strips help to stiffen the ceiling, and, being narrower than the ceiling joists, do not interrupt the key of the plastering so much. Housing consists of letting a piece of wood bodily into another for a short distance, or, as it were, a tenon the full size of the stuff; this is used in staircases, housed into the strings, and held by wedges. Housing is likewise adopted for fixing rails to posts, as in Fig. 487, where an arris rail is shown housed into an oak post for fencing.