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.
Owing to the universality of this joint it will be possible only to allude to one or two of its varieties. The ends of flitch girders and other large beams are bedded on stone templates to spread the weight, with or without asphalted felt or sheet lead as a bearing. When the beam acts as a tie, iron caulking plates or shoe plates are necessary to unite the ends to the templates. A small arch or cover stone will assist in preventing settlement from shrinkage, and in keeping space for a current of air, which should be provided for all round the end. Other timber girders and the heads and sills of par-titions are similarly treated, none resting over openings, and all fixed, where possible, with a clear air-space. Binding joists, if bedded on oak templates, may be bolted thereto, otherwise they may be fitted into the sockets of iron girders provided for them, or into iron stirrups passing over wooden girders, or they may be framed into the latter with a double tusk tenon. Tie-beams, if not cogged down to wall-plates, are sometimes fitted into cast iron tie-beam plates built into the wall and projecting therefrom. Common joists ought to be bedded without packing with chips or wedges, and well fitted and nailed down to the plates. When timber is bedded on metal, it is advisable to interpose a piece of sheet lead, with or without wedges, between the wood and the lead, for an air-space. Whilst timber remains dry its carbon is safe, but moisture induces chemical action and causes its loss. The bearings, therefore, should be kept dry, which may be effected by coating the perfectly-seasoned timber with asphalte, but is best accomplished by an air-space.
Bevel or Bevelled Joint is one in which the plane of the joint is oblique to the fibres of one of the timbers, and parallel to those of the other.
Bevelled Shoulder Joint is a variety of mortise and tenon used in uniting inclined to upright and horizontal pieces, and is made by cutting bevelled shoulders to the tenon on the inclined piece, as shown in Fig. 26, and a corresponding sinking or joggle to receive it on the cheeks of the mortise in the post or beam. By means of the joggle the junction is made more perfect, and its strength, as well as that of the framing to which it belongs, materially increased.
An angular notch at the end of a common rafter, strut, etc, taken out to enable it to fit snugly down on the arris of another piece upon which it abuts. Fig. 25 represents the usual form of the joint between a rafter and plate, or longitudinal bearer, effected by its aid. Birdsmouths are also advantageously used for the abutment of struts when the latter form acute angles with the rafters or other timbers they help to support, and when no cleats or straining blocks are permissible. There is no reason why a notch, as in Fig. 27, on the edge of a piece should not likewise be called a birdsmouth, since there is but little restriction in the other trades as to its position.