616 



Yearbook^ of Agriculture 1949 



woods. The final choice of the wood 

 may also be affected by the skill of the 

 worker and the availability of the de- 

 sired species. The farmer, for example, 

 who wants to use wood growing on his 

 own land has a limited selection and 

 may not be able to choose the ideal 

 wood for a given purpose, but with the 

 actual demands clearly determined, he 

 can make the most satisfactory and 

 economical selection from the wood 

 that he has. 



The characteristics vary among spe- 

 cies, among the individual trees of the 

 same species, and even among pieces 

 of wood taken from different heights of 

 the same tree. Thus the published 

 values for the different properties are 

 averages and do not hold for every in- 

 dividual piece of wood. 



One should also understand that 

 wood does not have the same strength 

 properties in all directions. Strength 

 depends on the direction of the grain. 

 When tension pull is applied par- 

 allel to or along the grain, for example, 

 wood may be 300 times as strong as 

 when the tension is applied at right 

 angles to the grain. 



The terms "hardwood" and "soft- 

 wood" are used to distinguish between 

 two general classes of wood and not to 

 indicate the properties of the included 

 species. Hardwood is the name given 

 to the group of trees that are broad- 

 leaved. Softwood is the name given to 

 trees that have needlelike or scalelike 

 leaves and are mostly evergreen (cy- 

 press, larch, and tamarack being 

 exceptions). 



The hardwoods are not necessarily 

 high in relative hardness; some woods 

 classed as softwoods are actually harder 

 than some classed as hardwoods. The 

 softwoods are used principally in con- 

 struction; the hardwoods furnish most 

 of the wood for implements, furniture, 

 and other industrial uses. 



The weight of wood in itself has an 

 important bearing upon the selection 

 of a species for many uses. Weight also 

 serves as a reliable index of the strength 

 properties of dry wood and affords an 

 accurate comparison between the 



strength properties of possible species 

 when the degree of dryness and the 

 actual sizes are the same. Generally 

 speaking, the heavier a piece of dry 

 wood, the stronger it is, regardless of 

 the species. 



Changes in temperature have little 

 effect upon wood; they cause such 

 small variations in size that for ordi- 

 nary farm and home uses the effect of 

 temperature can be overlooked. 



Changes in moisture content, on the 

 other hand, have a considerable effect 

 on wood, which swells as it takes up 

 moisture and shrinks as it dries. Diffi- 

 culties may be encountered if this prop- 

 erty is disregarded. When proper pre- 

 cautions are taken, however, most of 

 the trouble due to swelling and shrink- 

 ing can be avoided. The shrinking or 

 swelling in the width of a flat-grained 

 board is nearly twice that of a quarter- 

 sawn, or edge-grained, board of the 

 same width; the shrinkage or swelling 

 lengthwise of the grain in both is 

 negligible. 



One can compensate for high shrink- 

 age, if only that kind of wood is avail- 

 able, by using edge-grained pieces, 

 which will prove as satisfactory as flat- 

 grained stock of species that have lower 

 shrinkage values. Much trouble can 

 also be avoided by using only wood 

 that has been dried to approximately 

 the moisture content that the finished 

 piece will have in service. Thorough 

 air drying will take out about half and 

 thorough kiln drying about two-thirds 

 of the shrinkage of wood. That is 

 enough for the ordinary uses. 



Warping, which is the result of un- 

 even shrinking or swelling, may occur 

 in wood that is plain-sawed, or cross- 

 grained, or improperly dried. It can be 

 reduced to a minimum by the use of 

 edge-grained, properly dried material. 



Woods that are comparatively free 

 from warping include: Northern and 

 Atlantic white-cedar, eastern and west- 

 ern redcedar, cherry, chestnut, north- 

 ern white pine, ponderosa pine, sugar 

 pine, western white pine, yellow-pop- 

 lar, redwood, walnut, and the eastern, 

 Engelmann, and Sitka spruce. 



