It is a matter of considerable importance, in the framing of timber structures, to form each joint in such a manner that it may perform its particular office in the best possible manner. The functions performed by joints are very numerous, and it therefore requires a considerable amount of thought to select the joint best suited to any particular purpose, and to proportion its parts correctly.

The joints used in carpentry may be classified into three groups, as shown in the following table: -

Used for.

Technical Names of Joints employed.

Lengthening Joints.

Lengthening ties.*

Lapped (nailed, bolted, A, Fig. 250; strapped, B, Fig. 250).

Lengthening struts.†

Scarfed (plain, A, B, C, D, E, Fig. 251; bolted, F, Fig. 251).

Fished, A, B, C, D, E, F, Fig. 252.

Lengthening beams.‡

Fished, Fig. 252.

Lengthening wall-plates.

Halved, A, B, C, Fig. 253. Bevel halved, D, E, Fig. 253.

Dovetail halved, F, Fig. 253.

Pole-plates, etc.

Keyed, G, Fig. 253. Wedged, H, Fig. 253. Screwed, K, Fig. 253.

Bearing Joints.

Supporting beams on plates and beams on beams.

Abutted, A, Fig. 254. Housed, F, G, Fig. 254.

Notched, B, C, Fig. 254. Cogged, H, K, L, Fig. 254.

Mortised and tenoned, A, B, C, Fig. 255.

Tusk tenoned, A, B, C, Fig. 256. Housed tenoned, Fig. 257.

Supporting beams on posts and posts on beams.

Cleated, A, B, C, Fig. 259. Wedged tenoned, A, Fig. 260.

Mortised and tenoned, A, B, Fig. 258. Bridled, C and D, Fig. 258.

Dovetail tenoned, B, Fig. 260. Turk tenoned, Fig. 261.

Housed, Fig. 261.

Supporting ends of inclined timbers.

Bird's-mouthed, A, Fig. 263. Cleated, B, Fig. 263.

Connecting Joints.

Connecting struts with ties.

Abutment-plate, A, Fig. 264.

Plain abutment, B, Fig. 264.

Connecting struts with struts.

Tenoned abutment, C, Fig. 264.

Bridled, D, Fig. 264.

Connecting ties with ties.

* The term tie is applied to members of a frame structure which have to resist a tensional stress.

† The term strut is applied to members of a frame structure which have to resist a compressional stress.

‡ The term beam is applied to members of a frame structure which have to resist a transverse stress.

Principles Of Joint Making

In making joints in woodwork the following five principles should be borne in mind: -

1. All cutting must be performed in such a manner as to weaken the timbers as little as possible.

2. Where possible, abutting surfaces should be perpendicular to the pressures brought upon them.

3. The area of each part of the joint and its fastenings must be proportioned to resist the maximum stresses brought upon them.

4. The joints and fastenings must be so proportioned and fitted as to cause the stresses to be spread as uniformly as possible over their sections.

5. The joints must be formed so as to be affected as little as possible by shrinkage or expansion of the wood.