1306

THEORY AND PRACTICE OF ENGINEERING.

Book II.

SHOULDER JOINTS.

The common method of effectingsuch a junction does not occupy somuch time or labour, but is not soeffective ; it is usual to drive one ortwo wooden pins through holes boredfor the purpose at right angles throughthe timber, in which the mortise ismade as well as through that whichhas the tenon.

Boring the hole for the pin requiresto be nicely performed, in order that itmay draw the tenon tight into themortise prepared to receive it, andmake the shoulder butt close into thejoint, without running the risk oftearing out a portion of the tenonbeyond the pin: square holes andsquare pins are preferred to round,as they bring more of the wood intoaction, and there is less liability to split. *

Fox Tail Wedging y adopted by ship carpenters, is made with long wooden bolts, which donot pass completely throughthe timbers, but take a veryfast hold ; they are subject tobe crippled in drawing, if theyare too nicely fitted ; this isremedied by placing a thinwedge into the hole previousto the insertion of the woodenbolt, which, when driven, issplit by the wedge, and thussqueezed tight to the sides ofthe hole.

Bond Timbers and WallPlates require to be carefullynotched together at every'angle and return, and scarfed at everylongitudinal joint. Fig. 2071. halving.

To make a good tie joint requires great attention on the part of the carpenter, and foruniting wall plates the dovetail joint is sometimes adopted: if the effects that shrinkingmay produce be taken into consideration, the more usual system of halving is decidedly pre-ferable ; whenever this joint is employed, a stout pin oftough oak, or an iron bolt, should be driven through torender it secure, and, where there is the slightest tendencyfor one piece to slide from the other, iron straps must beused.

Timbers which are laidupon the Plates , and in-tended to act as ties,should be cut with adovetail, and let into thetimber it is to secure;generally, where theycross at right angles,halving or cutting awaythe moiety of each isadopted, and one is letinto the channel cut inthe other.

Cauking , or dovetailinga cross, as used for fittingdown tie-beams or othertimbers upon wall plates,should never be made toolarge, nor too near the Fi S- 2073 ' cavking joints. Fig. 2074.

ends of the plates, the grain of the wood, if cut across, being very liable to split off; it maybe observed that the dovetail joint so frequently referred to is not so termed on the Continent,but is universally known as the swallow-tail, queue d'hirondelle.

Fig. 2070.

HALVING.

Fig. 2072.

DOVETAIL JOINT.