. The teacher's handbook of slöjd : as practised and taught at Naäs, containing explanations and details of each exercise. 3-04 6-59 8-88 6-25 5-49 4-89 As is seen from the above table, the degree of shrinka
. The teacher's handbook of slöjd : as practised and taught at Naäs, containing explanations and details of each exercise. 3-04 6-59 8-88 6-25 5-49 4-89 As is seen from the above table, the degree of shrinkage inthe direction of the length of the wood is so slight that itmay be left entirely out of consideration. In the directionof the breadth, however, it varies from 2 per cent, to 9 percent. In radial section, the general average is 5 per cent.; forfir and pine 3 per cent.; for birch 4 per cent. In tangentialsection, where shrinkage is greatest, it varies from 2 per cent,to 13 per cent., the general average for wood in common usebeing 7 per cent.; for fir and pine 6 per cent.; for birch 9per cent. WOOD, OR TIMBER. 39. When a tree stem issawn up into planks by-parallel longitudinal cuts,the planks shrink as isshown in Ym. 4. Thebroadest portion shown,which includes the pith,shrinks least in breadth,Fig. 4. Shrinkage in planks. most in thickness ; least nearest the pith, most near the sides. The outermost plank,however, shrinks most in breadth—in the direction of theannual layers—and least in thickness. The planks lyingbetween shrink differently on different sides, and becomeconcave to the pith, and convex on the other side. Of trees in most general use, beech, lime, hornbeam, andpear shrink most; birch, apple, white-beam, walnut, ash, andoak shrink considerably; alder, maple, Scotch fir, elm, sprucefir, and larch shrink in a medium degree. Mahogany shrinksleast of all timbers. Cracks occur in timber, because, as indicated above, it isseldom uniform in texture, and it is the
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectmanualt, bookyear1892
