Circular joints, especially for very heavy framework, have been recommended by Tred-gold, Robison, and other writers, but theoretically they are not to be defended, and practically they are seldom, if ever, used.
It will be seen that a kind of mortise is cut in the post to fit the bridle, or projection (b b), left upon the beam.
Figs. 189, 190 show a bridle joint for the junction of the foot of a rafter with a tie beam. A similar joint may be used when the head of the rafter meets the king post. Such a joint, with the peculiarity of a circular abutment, is shown in Fig. 187.
The bridle joint is sometimes made use of in practice, and is strongly recommended, in all its forms, by Tredgold, on the ground that every part of it can be thoroughly seen into before it is put together, and can therefore be more easily fitted than the mortise and tenon.
Fig. 186. Chase-Mortise.
Fig. 187. Circular Joint for head of Queen Post.
Fig. 188. Bridle Joint between Post and Sill.
The width of the bridle should not, if possible, exceed i of that of the beam, otherwise the cheeks, or pieces winch fit on each side of it, will be weak, and liable to be wrenched off by a slight lateral pressure.
Fig. 189 is the elevation of the foot of a principal rafter united to the tie beam by a bridle joint. Fig. 190 shows the timbers detached so as to make clear the construction of the joint. The joint in Fig.
189 is assisted by a heel strap, for a description of which see p. 80.