MODE OF USING SAWS. 



191 



as shown by the " Nonpareil " saw. Triangular or dog-teeth 

 should be f inch high and J inch wide. The spacing between 

 the teeth should be double their width, and this suffices 

 for coniferous as well as broadleaved wood. Wider spacing 

 than this, by reducing the number of teeth, impairs the 

 efficiency of the saw. The slit made in a piece of wood 

 by a saw is termed the kerf. 



The teeth are sharpened with a triangular file (better with 



111. Sharpening of the teeth. 



a two-faced one), and this should be done until the sides of the 



teeth that meet the wood are as sharp as knives. Saws which 



work both ways must have their teeth sharpened on both sides, 



but one-handed saws on one side 



only. As all forest saws are set, 



the stroke of the file must be 



always, as in Fig. Ill, on the 



inner side of the teeth. When a 



saw has been properly sharpened, 



the tops of the teeth must not 



project above a general line, or 



the projecting ones will be broken. 



A good saw in constant use will * >mted s:iw - bladc ' 



require sharpening only every five or six days. 



It is highly important that the teeth should retain their 

 proper shape, while constant use of the saw and frequent and 



Fig. 1 1 3. Perforated saw. 



unskilful sharpening gradually alter it. Messrs. Dominicus & 

 Son, of Eemscheid, have introduced perforated saw-blades by 

 which this defect maybe remedied. Fig. 112 shows how this is 

 done, and how the teeth drawn successively on the blade below 

 the original set can be filed down gradually by the workmen, 



