A mitre joint is made by beveling the parts joined so that the plane of the joint bisects the angle. It is used in making the external angles of bases, all horizontal mouldshown at B, where the dotted lines show the pieces when first joined, and the full lines show the pieces after they have shrunk. It is not uncommon to see door and window casings that have shrunk so as to open the joint a quarter of an inch. This, of course, looks very bad, and hence the mitre joint should only be used when the wood is thoroughly kiln-dried and not allowed to swell afterwards, as no mechanical device will prevent wood from shrinking.
With a true mitre all parts of the mouldings intersect perfectly, as at A Fig. 201.
When skillfully done the mitre makes the handsomest joint, and in many places, as with panel moulds, it is the only joint that is practicable. A mitre joint, however, has the disadvantage that any shrinkage in the wood causes the joint to open at the inner edge, a*
Fig. 202-Coped Joints.
Mitre Joints for Bases, Wainscoting, Built Posts, etc. - In the cheaper grades of work the pieces are simply mitred and glued or nailed together. Such a joint is not very strong, as the glue does not hold very strongly on the end wood, and neither do nails. When a plain mitre is used in cabinet work, the edges should be grooved and a hard wood dowel should be glued and driven in, as at C, Fig. 201.
A still better joint is that shown at D, as the parts can be securely nailed from both faces, and portions of the joint are parallel with the grain. Where internal angles are mitred and glued before putting up, the joint may be strengthened by inserting thin strips of hard wood, called "keys," in the back of the joint, as shown at E. These may either be horizontal, as at K, or inclined, as at k, the latter being the stronger. All of these joints, slightly modified, are applicable to acute and obtuse as well as to right angles.
For first-class work all mitre joints should be glued and further strengthened by dowels, blocks or brads. Mitre joints for casings are described in Section 168.
Coped Joint. - A coped joint is only used in connection with mould-dings ; it is made by cutting the end of one moulding to fit the profile of the other, as in Fig. 202. When nicely made a coped joint cannot be distinguished from a mitre joint, that is if the mouldings are alike and not too elaborate. When one moulding comes against another of a different pattern, the one which is stopped should be coped to the other.
A coped joint has the advantage over the mitre joint in that any shrinkage in the piece that is coped does not open the joint, and if the other piece shrinks the joint does not open as badly as with a mitre joint. Only comparatively plain mouldings, however, can be successfully coped.
Covered and Housed Joints. - The author has used the term "covered joint" to designate those joints in which the edge of one part laps over on to the face of the other, usually from 3/8 to 1/8 inch.
When two pieces of finish are joined parallel with the grain a covered joint should be used when possible, as it permits the parts to shrink moderately without opening the joint. The joint is usually made by rebating or ploughing the edge of the projecting piece, as at A and B, Fig. 203. Rebated or ploughed joints are always used in making paneled work, and with raised mouldings, back bands, etc.
A Moused Joint is one in which the end or edge of one piece is wholly let into the side of the other, as at C, Fig. 203. Housed joints are used principally in joining the ends of stair treads and risers to the wall string, and to a closed string, and in uniting the angles of cisterns and tanks. It makes a strong as well as a neat joint for such places. A ploughed joint like that at A, Fig. 200, is sometimes called a housed joint, but the author prefers to confine the latter term to a joint like that at C, Fig. 203.
Fig. 205. - Common Dovetail.
Fig. 206 - Lapped Dovetail.
Fig. 207. - Secret Dovetail.