This section is from the book "A Practical Treatise On The Joints Made And Used By Builders", by Wyvill J. Christy. Also available from Amazon: Practical treatise on the joints made and used by builders.
Pulley Mortise Joint is another term for a chase mortise joint.
Radiating Joint is made when the direction of two or more joints tends towards a centre or axis. For instance, the crossed joints of the back-pieces of centerings, and those of curved ribs put together in thicknesses, as well as the heading joints of circular curb-plates, belong to this denomination.
This, like the similarly-named joint noticed in some of the other sections, occurs when a rebate or rectangular one-sided groove constitutes one of the meeting surfaces. Out of numerous instances of the adoption of the rebate in carpenter's work, may be mentioned its usefulness when gate posts are checked for heavy gates moving on central pivots to close snugly into them.
A post or strut with rounded hutment affords an illustration of this description of joint. It is calculated that with posts of equal length and scantling, the compressive resistance offered by square ends is three times that of rounded ones when left free to move.
This is made by the operation of scarfing, which consists in uniting two pieces of timber longitudinally by similarly halving, toothing, or more or less intricately tabling and indenting both to the same templet, and then lapping their ends and tightening all up with folding or keyed wedges in a central mortise, (but not with such tightness as to instigate straining), and finally strapping or bolting with washers or iron plates. The simplest kind occurs in lengthening wall plates, and is nothing more than halving the ends together with splayed surf aces without any fastening but spikes, Fig. 53, and out of many other complicated varieties may be mentioned those formed with a third piece of shorter length mutually connecting the longer ones, as shown in Fig. 54. The parts of each timber running with the grain, or nearly so, that come in contact in the joint are called scarfs, a term intimately associated with calf or kerf, signifying the wedge-shaped part formed by cutting the end slantingly. Scarfing usually runs in such a direction that when the lengthened beam is in position the planes of the tabling lie horizontally, or else inclined to its upper and lower edges, but when a transverse strain has to be encountered, it is better that these planes should run vertically between the sides of the beam, the joint being placed where the strain is not the greatest, or as far from the point of maximum strain as possible, or where if feasible the beam can be upheld by a post or suspending piece. Fish plates are employed to prevent the bolt heads and nuts crushing the timber, and not as in fishing, to form the bond. Sometimes, however, the ends of the fish plates are turned down and let into the wood to increase the tensile strength, in which case opposite ones ought not to enter or be too close to the same cross section, otherwise its effective area might be diminished to a risky extent. Straps and bolts are often used instead of bolts and plates. Scarfing, as a rule, but not universally, preserves the same width and depth of beam throughout, and it characteristically differs from fishing in the ends interlocking and mutually filling up their respective voids, instead of simply butting. It is used for piecing vertical timbers; but though some ways of making the joint will do equally well for compressive and tensile stresses, in most cases the nature of the chief force to be resisted must be considered before choosing the precise form. Oblique bearing surfaces are weak against compression, as they may slide and cause splitting with a wedge-like action, and, moreover, intricate forms are often weak and dangerous, for unless the projections all bear against their corresponding indents, which requires excellent workmanship to insure, the strength is reduced by each additional scarf. Roughly speaking, the length of the joint should average about four times the depth of beam when bolts and indents enter into it. Other varieties of scarfs are shown in Figs. 55, 58, 64, and 65.