It frequently occurs in the practice of carpentry, that single lengths of timber are too short for the distance required; in which case, the carpenter unites two or more pieces by a process technically termed scarfing. The principal end to be attained is, that, when put together, the scarfed stick shall be equal in strength to a single piece of the same dimensions. To attain this, it is necessary so nicely to adjust the indentations, that the entire surface of each part shall come in contact with the corresponding part in the other piece; so that all may have a direct and uniform bearing, and none be made to resist a force that should be resisted by another.

Methods of scarfing are various; and, of many, we may truly say, that their design savors more of the imagination of the artist than the sober experience of the mechanic.

As it is not the purpose of this work to illustrate the whole range of experiments in these things, such methods only will be given as have proved themselves most useful, presuming these will meet every reasonable demand; remarking merely, that, when more complicated forms of indentation are made, it is always at the expense of utility.

Beams are seldom exposed to more than two kinds of strain which act upon the scarfing. One is, when the power is so applied as to exert a strain in the direction of the beam's length, as that produced by truss-rafters on a tie-beam: the other is, when the force or power tends to sag or break the beam in the direction of its depth.

In consideration of which, attention should be paid, in the selection of a method of scarfing, to the particular kind of strain to which the beam is most liable to be subjected.

The parts of a piece of scarfing are held together by bolts passing through the stick, as shown in the plate; and oak-keys are frequently put into the scarf to prevent the parts sliding past each other, as seen at a, Figs. 1, 2, 3. Care should be taken that neither bolts nor keys be so large as to require the removal of such an amount of wood as will materially weaken the timber.

These keys should he made of perfectly sound dry white oak. They should be in two parts, each slightly tapering on one side, so that, when driven in, they may tighten the joint.

The iron straps or bars used on a scarf (as shown on some of the examples) should be of the best wrought iron, from a fourth to a half inch in thickness, and from two to three inches wide, according to the size of the beam scarfed; and should be four in number to each scarf. The length of the scarfing for any beam should be about six times the depth of the stick, and the bolts which confine the work together should be from a half to three-fourths of an inch in diameter; making five-eighths of an inch as the best average size for bolts to beams of any dimension above eight or nine inches square.

Plate III

Plate III. exhibits five specimens, or examples, of scarfing. Figs. 1, 3, and 5 are best adapted to resist a strain in the direction of the length of the beam; and Figs. 1, 2, and 4, to resist one in the direction of its depth. In Figs. 4 and 5, the pieces are too short to admit of either of the other methods. The planks of example at Fig. 5 should be of good dry white oak; and, if the work is well done, this scarf is equal in strength to either of the more complicated methods. This practice is called by carpenters "fishing a beam."

It is well to observe here, that the examples cited as being particularly adapted to resist a longitudinal strain are also capable of sufficiently resisting a vertical one.

Scarfing

Pl.III

Smith Knight & Tappan.Engrs..