200 



P^ELLIXO AND CONVERSION. 



(b) Mode of Construction of Saws. — Saws are constructed 

 differently accovdinj^' to the uses tor wliicli they are intended ; they 

 vary in shape, length, weight, and shape of teeth. 



Tliey may be used either for large or small timber. In the 

 former case they cut both ways, and are worked by two men, and 

 termed two-handed saws. In the latter case they only cut one 

 way and are one-handed : such saws rarely exceed Ih to 2i feet 

 in length, whilst the two-handed saws may be 3.\ to 6^ feet long, 

 their length being determined by the diameter of the piece to be 

 sawn, and the distance through which the arm moves. The 

 weight of a saw also depends on its length. 



The construction of the teeth of saws varies considerably. 

 Each tooth may be either symmetrical or unsymmetrical, and 



Fio (57. Fig. <){>. 



b 



vary in depth, thickness and distance from one another, each ot 

 which points affects the working of the saw. 



As regards the shape of the teeth, a distinction must be made 



Fig. 69. Fi«- "0- 



//AA 



between those cutting one or l)oth ways. In llie former case 

 they are usually shaped as in tig. 67, that of a right angled tri- 

 angle, the shorter side of the triangle or face of the tooth being 

 at ri'dit anjfles, or nearlv so, to llic line of their inst-rtion on 



Fic 



M j^J-^ J^/_^A_A/L 



the saw. In Knglisli saws the liypotbenuse, or buck of the 

 teeth, is cut-out in a curve (tig. (58). Such teeth are only used 

 in the case of one-handed saws, or in pit-saws used by wood- 

 cutters for sawing timber longitudinallv- 



