OF SCARFING, &C; 



267 



wexion. Such a method of lengthening a tie is shown by the fol- 

 lowing figure ; and is what ship-carpenters cs.[]Jishing a beam. It 

 is obvious, however, that the strength in this case depends on the 



Fio. 55. 



^T T 



' T + 1 + ^ + ' 



bolts, and the lateral adhesion and friction produced by screwing 

 the parts together. 



The dependence on the bolts may be much lessened by mdent- 

 ing the parts together, as shown by the upper part of the annexed 

 figure ; or by putting keys in the joint, as shown by the lower side 

 Fig. 56. 



of the same figure ; but the strength of the beam will be lessened 

 in proportion to the depth of the indents. 



The only reasons for not depending wholly on bolts, are, that 

 should the parts shrink ever so little, the bolts lose a great part of 

 their effect ; and the smallness of the bolts readers them liable to 

 press into the timber, and thus to suffer the joint to yield. 



The sum of the areas of the bolts should never be less than two- 

 tenths of the area of the section of the beam ; and it is not a good 

 practice to put the bolts near to the end of the pieces. 



The most usual method of joining beams is that called scarjiiig, 

 where the two pieces are joined, so as to preserve the same breadth 

 and depth throughout ; and wherever neatness is preferable to 

 strength, this method should be adopted. 



From Fig. 57 to Fig. 60, four methods of scarfing are shown. 

 The first, Fig. 57, is the most simple ; it depends wholly on the 

 bolts, and in this and like cases, it is best to put a continued plate 

 of iron on each side for the heads of the bolts. The ends of the 

 plates may be bent and let into the beams. 

 Fig. 57. 



