The Technique of FURNITURE MAKING
FELLING AND SAW-MILLING
Exceptionally valuable timbers standing alone or in isolated groups are usually bargained for separately; each tree is measured and the price per foot cube of usable timber in each butt negotiated.
It is customary to fell standing timber in autumn and winter, although there is no real objection to summer felling, for a growing tree can transpire up to 50 gal (227 1) of water a day through its leaves in hot weather, thus depleting the moisture content of the trunk. However, summer felling does increase the risk of too rapid drying and consequent severe checking and splitting of the logs, and therefore winter schedules are usually adopted. Tropical timbers are felled at any time dependent on the prevailing conditions, for they have no fixed period of growth (and therefore no pronounced annual rings), while certain heavy timbers, notably teak, greenheart, etc., are girdled or ring - barked at the base of the trunk about two years before felling, thus cutting off the supply of food and sap. As the tree continues to transpire through its leaves the overall weight is drastically reduced, enabling it to be hauled or floated.
If a tree is a large one and the timber above the first main break is usable, then the whole trunk is felled and taken to the saw-mill; alternatively the second length above the break (branch or fork) is split for cordwood, and only the butt or main trunk is used. Except in tropical rain forest trees, where lack of light and overcrowded conditions encourage very straight, clear cylindrical poles often up to 180 ft (55 m) high in emergent trees, second length timber is usually inferior in quality, with large knots, twisted grain and a much smaller percentage of heartwood. Such timber is, therefore, only suitable for building construction work, although an occasional second length will yield good-quality narrow planks. Branches are not used, for not only is the proportion of heart - wood very small but the pith is off centre, with the annual rings in tension at the top and in compression underneath, therefore causing considerable shrinkage. Occasional prime walnut, mahogany and ash trees, etc. yield at the convergence of the two sets of annual rings the exceptionally beautiful crotch, curl and feather figuring, while good burrs or burls, when they occur, are cut off and sold to the veneer - merchants. The stumps or root bases of some walnuts, notably the American black walnut, can also yield the very bold stump figuring, and these trees are uprooted bodily and not felled. It is a little sad for the craftsman that all the best of timber—prime oaks of 40 in (1 m) quarter girth and up, fine walnuts, clean sycamores, and in fact all exceptional trees—are immediately bought for veneer cutting at prices far higher than they would reach for conversion into solid board and plank.
Home-grown hardwood logs are not debarked at the saw-mill, for, although the bark does encourage insect pests, it. helps to protect the trunk from over-rapid drying. Imported timbers are, however, always debarked, and sometimes also desapped which helps to cut down the weight, for the logs are sold with the customary allowance for bark and wane, and there is little point in incurring heavy transport costs for useless tonnage. Where logging costs are high, with long distances to be covered, and where there are ample forest reserves to cover the capital costs, local saw-mills are usually erected to convert the logs into square edge timber or lumber. Teak and other valuable hardwoods are invariably exported square edge, while most of the common woods can be obtained in round logs trimmed of sap or in square edge timber, the latter usually only 'shipping dry', with a moisture content below the danger level for fungus attack (25 per cent), but otherwise unseasoned.
