Lengthening Of Beams. Where "beams" are required of such lengths as prevent them being in one piece, two beams are lengthened by joining them in various ways. The simplest and the strongest mode of joining two timbers together in the direction of the r length is what is known as "fishing." In this the two beams a and b, fig. 322, to be joined, have their ends carefully squared off, and made to butt against each other at c; they are kept together and secured by the flat pieces of timber d d, e e, one placed at the upper, the other at the lower edges of the two beams; holts , f g, pass through the "fishing pieces" d d, e e, and the beams a b, and are secured by nuts at the end; the nuts should be screwed tightly up, as on these depend the strength of the joints. As they are apt to be indented into the wood, plates of iron, as i, fig. 322, are sometimes placed beneath the bolt-heads and the nuts, or in place of the fishing pieces being of timber, as at d d, they are of iron, as shown at j. Usually two fishing pieces are employed, as in fig. 322 at d e; in some cases, however, fishing pieces are placed at the sides of the beams, thus enclosing them, as it were, and as illustrated at h. As said above, the method of "fishing beams" is the strongest employed, but it is obviously unsightly and clumsy, in consequence of the projecting parts, as d d, e e. To avoid this, the fishing pieces are sometimes let into the surface of the beams wholly, as at l, fig. 322, or partially, as at k, same figure; but this method, although adding to the sightliness of the joint, greatly takes from its strength. Other methods are therefore adopted, where appearance can be gained without sacrificing the strength of the joint too much. The principle upon which those other joints are made is that known as scarfing, which enables the joint to present a smooth, or rather flush appearance on all sides. The simplest form of scarfed joint, known as the half lap, with flat or rectangular "tables," by which term the projecting parts or scarf joints are designated, is illustrated in fig. 323. In this a part a b c is cut out at the end of each beam, equal in depth to half of the full depth of beam, and of length equal to the required length of scarf. The two ends, when brought together, form the joint, as in fig. 323, the projecting part of one, as d, falling into the recessed part e of the other. The two are secured together by the timber or iron plates f, g, and by screw bolts and nuts; h i j k I show different sections.

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Fig. 322.

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Fig. 323.

The plates are better when extending beyond the ends of the joints, as shown in the drawing. In place of being short they may be as long as shown by the dotted line n. In addition to the bolts and nuts, "keys," as o o, are sometimes added. Fig. 324 illustrates another form of the "half-lap " joint, A being vertical section, B horizontal section on the line a b'. A very common form of scarfed joint, with angular or oblique "table," is illustrated in fig. 325, where the meeting faces of the two beams, a and b, is oblique, as at cc; the ends being indented angularly, as at d e; the two being secured together by the plates f f, g g. Another form of scarfed joint, with three tables, is illustrated in fig. 326 - a b, the two beams; c c, the oblique tables, an iron plate d d securing the two. At A a scarf joint with five tables is shown, B the plan.

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Fig. 324.

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Fig. 325.

24 Lengthening Of Beams 14324 Lengthening Of Beams 144

Fig. 326.