SAWMILLS. 489 



Saws for hardwoods and for resinous, knotty wood of many 

 conifers should be thicker than those used for soft, clean- 

 grained coniferous wood free from knots. For blades of 

 moderate length 1 to 2J mm. may be considered the best 

 thickness for saws. Saw-blades are made now even thinner 

 than this, while formerly blades 5J to 7 mm. thick were used. 

 Thin blades give a cleaner cut than thick ones. A good blade 

 should also thin off towards its back. From average annual 

 results recorded in the Harz mountains, it appears that with 

 old thick saw-blades the saw-dust amounted to 10 or 11 per cent, 

 of the whole butt sawn, whilst with thin blades it is only 2j per 

 cent. There are, however, in the large coniferous forests, where 

 the price of wood is low, many sawmills where the loss of wood 

 still exceeds 12 per cent. 



6. Set <>/' tin' Sate. 



The extent of the set of the saws also influences the loss of 

 wood considerably. Setting facilitates sawing, but only at the 

 expense of the outturn, both in quantity and quality. Old- 

 fashioned saws working in wood of good quality usually have 

 a set of 0'75 to TOO of the thickness of the blade, causing the 

 werf to be often 7 mm. and more. Attempts have recently been 

 made either to dispense altogether with the set or reduce it as 

 much as possible. 



7. Length <>/' ni<le. 



The length of the saw depends on the thickness of the butts 

 and on the play of the saw (i.e., double the length of the 

 crank g, Fig. 296). The shorter the blade the greater its 

 possible tension and the cleaner it cuts. The shortest length 

 possible is double the thickness of the largest butt which is to 

 be sawn. In a good sawmill this minimum should be exceeded 

 only slightly ; evidently the play of the saw must correspond 

 with this. 



8. Mode of Fixing Butts on the Carriage. 



The butt must be fixed firmly to the carriage, so that it 

 remains rigid while being sawn. Numerous contrivances have 

 been invented with this object in view. 



