14 TROHNIOAL PnOPERTIES OF WOOD. 



depends on the closeness of texture of the -wood, the toughness 

 length and tendency to twist or anastomose of the fibres, and the 

 quantity of moisture present. It will hence be understood why 

 light wood with tough fibres requires a heavier axe than heavy 

 wood with short fibres. The axe not only cuts but also presses, 

 and tough loose fibres give before the passage of the axe, being 

 merely pushed forward. In every case the resistance offered to the 

 axe is greatest at right angles to the fibres, and diminishes in 

 proportion to the obliqueness of the stroke. 



The resistance offered to the saw does not resemble at all that 

 offered to the axe. Contrary to what happens in the case of the 

 axe, for most species, especially those which are light and tough, 

 the resistance is greatest in the direction of the fibres, since the 

 saw has no splitting action, but takes off a string of fibres, shred by 

 shred, whether cutting along the fibre or across it. The teeth of a 

 saw work principally by tearing, very little, sometimes, as in wood of 

 loose texture, not at all, by a shaving or cutting action. Hence 

 the tougher and longer the fibres are, and the looser the structure 

 of the wood, the more difficult is the work of the saw, for the teeth 

 then no longer break up or divide the individual fibres, but tear 

 them asunder from one another, owing to which circumstance the 

 sides of the cut become rough and uneven, a large quantity of 

 coarse sawdust is produced, and the saw has to overcome a very 

 great amount of friction. In the case of wood of compact texture 

 and possessing short and closely-cohering fibres, the fibres are 

 more easily broken or otherwise divided, the sides of the cut are 

 smoother and the sawdust finer and less abundant. It is thus a 

 general rule that amongst broad-leaved species the heavier and 

 denser kinds are the easiest to saw. Resin and other glutinous 

 secretions clog the teeth of the saw, and increase very considerably 

 the friction. Nevertheless, the conifers, although also loose tis- 

 sued, are easy to saw because of their extremely regular structure. 

 As a rule, green wood is easier to saw than dry wood, since, as we 

 have seen above, moistare renders wood softer, although the fibres 

 themselves become less brittle. The only exceptions to this rule 

 are woods with very loose texture and long tough fibres, which are 

 rendered all the tougher and stronger by the moisture. 



According to Gayer, if we denote the resistance offered by re- 

 cently-felled beech to cross-cutting with the saw by unity, the corre- 

 sponding resistances offered by other species are — spruce = O-fiO 

 Scotch pine = 0-67, silver fir = 0-76, larch = 0-93, oak and 

 aspen = 1-09, alder = 1-10, birch = 1-35, willow = 1-37, lime 

 or linden = 1"77. 



