<582 SAW-MILLS. 



coniferous wood free from knots. For blades of moderate length 

 13 to 2.V mm. maybe considered the best thickness for saws. 

 Saw-blades are now made even thinner than this, while formerly 

 blades /5i 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 % of the whole butt sawn, whilst 

 with thin blades it is only 2h %. There are, however, in the 

 large coniferous forests, where the price of wood is low, many 

 saw-mills where the loss of wood still exceeds 12 %. 



6. Set of the Sate. 



The extent of the set of the saws also considerably influences 

 the loss of wood. 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 I'OO 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. Le)tijth of Blade. 



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. 300). 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 saw-mill this minimum should be only slightly exceeded ; 

 evidently the play of the saw must correspond with this. 



8. Mode of Fixinrj Butts on the Carriage. 



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

 remains rigid while being sawn. Numerous contrivances have 

 been invented with this object in view. 



