Figure 9. A beam of two thicknesses bolted together, the scarfing of each length of timber alternating in the two thicknesses, so as to have the junction of two lengths in the one thickness opposite the centre of a length in the other thickness : the scarfing is similar to that of Figure 3.
Figure 10. A beam of three thicknesses bolted together, each thickness consisting of a number of short timbers so disposed, that the joints in no thickness come opposite the joints in either of the other thicknesses ; a bolt occurs between every two joints.
Figure 11. A section of a girder with two braces and a king-bolt.
Figure 1'2. The section of a girder with a straining piece, two braces. and two truss bolts. of the best principle. No. 1 represents the girder laid open, in order to show the core. No. '2, the two parts bolted together. No. 3, the of a washer, No. 4, the face of the same. Nu. 5. the side of the cut metal bolts, in the transverse direction of the girder. No. 6, the side of the same, in the longitudinal direction. No. 7, the transverse direction of the truss-loth, or king-bolt.
Figure 13. The section of a girder. calculated from its rise to sustain very heavy weights. It' the tie-beam he very strong, the abutments may be wedged ; but then the wedges ought to be very long, the tapper very small, that there may be no inclination to rise. The excess of length may be cut off afterwards. The bolts represented at No, 5, and No. G, Figure 12, are nevertheless to be preferred.
Two timbers may be joined, either by making both planes of contact parallel with or at right angles to the fibres, or by making the joint parallel with the fibres of the one piece, and at right or oblique angles to those of the other, or at oblique angles to the fibres of both pieces. When two of timber are joined so that the common seam runs parallel with the fibres of both, the joint is called a longitudinal joint ; but when the plane of the joint is at right, angles to the fibres, it is an abutting, or lodt-joint ; this position brings the fibres of both pieces in the same straight line. If' the joint be at right angles to the fibres of one piece, and parallel with those of the other, it is called a square joint ; it' the joint be parallel with the fibres of one piece and oblique to those of the other. it is a bevel joint ; and lastly, if the joint lie at oblique angles with the fibres of both pieces, the fibres an angle with each other double to that formed by the fibres of one piece and the joint, it is ti mitre joint.
These are the general positions of simple joints in respect to the fibres of one or Loth picees ; those m hick may be coin pounded by the position of dillerent planes, are of infinite variety, but as they seem to have little or no practical appli cation. we shall not detain the reader longer on the subject. In fixing two pieces of timber together with longitmlinal joints, the pieces arc generally bolted, and sometimes pinned.
As to butting and mitre joints, they are seldom or never used in carpentry.
When two pieces of timber are joined together at one or more angles, the one piece will either meet the other and one angle. or by crossing it two angles; or the two timbers will cross each other, and form timr angles.
In all the following eases of connecting two timbers, it is supposed that the sides of the pieces are parallel with the fibres. or, if the fibres be crooked, as nearly so as possible ; and that each piece has at least one of its surtimes in the same plane with those of one of the other ; the four sides being at right angles to each other.
The angle or angles so formed will either be right or obtuse. Notching is the most common and simple fitnn, in permanent works, and in some eases the strongest, fir joining, two tim bers at one or more angles, particularly when bolted at the joint. The form of the joint may be varied according to the position of the sides of the pieces, the number of angles, the quantity and direction of the stress on the one or both pieces, or any combination of these circumstances.
lit the notching of timbers upon each other, the notch is generally supposed to be formed by planes. at right angles to, and parallel with the side in which the excavation is made ; theretlire the part of the corresponding piece most have its planes in a similar situation. the solid being contained between these planes, instead of the empty space, or notch. as in the other. It may tits() here be remarked. that the notch is gin Tally supposed to consist of three planes, unless it be otherwise Notching admits of the two pieces being joined at from one to limn- angles ; hot joining by mortise tenon admits only from one to two angles.