Manufacturing Processes and Methods.— The processes involved in converting timber into lumber fall into two principal divisions, Logging and Sawmilling. In all sections of the United States except the North Pacific coast these processes are commonly found as departments of a complete lumber manufactur ing enterprise. In the States of Washington and Oregon, logging is frequently a separate business, and the sawmill buys its logs from logging contractors.
The first essential of a lumbering enterprise is a supply of timber within reasonable distance of the manufacturing point. On account of the bulky character of the raw material it can not be hauled long distances for manufacture. The timber supply must be sufficient to amortize the plant investment in a reasonable term of years and the size of the plant will depend, usually, on the amount of tributary timber. The average life of a sawmill ranges from 15 to 30 years, depending on the locality and the character of the timber and plant.
In the early stages of the industry the raw material was usually conveyed to the mill by floating the logs down a stream or by hauling over snow and ice-covered roads during the winter season. These methods are still prac tised in some places, but in the majority of lumbering operations a railroad for handling the log supply is part of the enterprise. This railroad consists of a "main-line" which is of permanent character, and logging "spurs" which are projected into the timber and moved from time to time as the timber is taken out.
Trees are felled by hand labor and are cut into log lengths by hand labor or by power drag saws. They are then hauled to the rail road or ((tram" either by the use of oxen or mules or by the steam askidder, a machine operating on the railroad track which by means of wire cables and grapples pulls the logs to the railroad right-of-way. There they are picked up by a steam loader, which is a crane with swinging boom, and loaded on cars that are especially designed and equipped to handle logs. When a train of these loaded cars is made up, they are hauled to the mill and there dumped into the log pond or, if heavy hard woods, "banked" or piled to await their entry to the mill. Where a pond is employed, it facilitates handling and sorting the logs, and also tends to clean them and keep them wet and in good condition for the saw.
The sawmill itself is apt to vary in equip ment from a single circular saw, the simplest type, to one or more band saws with gang saws, resaws, edgers, trimmers and a variety of other high speed machines, and may range in capacity from a few thousand feet a day to 1,200,000 feet daily, board measure, which is the capacity of the largest mill in operation.
The product of the sawmill is rough lumber and the manufacturing operation may stop at this point; on the other hand, a planing mill may be operated as an accessory, its function being to surface or °dress° that portion of the sawmill product that requires such treat ment, the equipment of the planing mill con sisting of high-speed power machines of van ous types for turning out smooth surfaced lum ber, moldings and like products.
The lumber as it comes from the saw is °green* or wet and must be dried before it is shipped to market. This is accomplished by piling it on the yard in such manner that every piece has adequate ventilation, allowing it to stay in pile until it is "air-dried," or by putting it through the steam dry kiln, which by sub jecting it to degrees of heat and moisture that are scientifically determined according to the wood and its thickness dries it rapidly. The process of kiln drying is a delicate one, because too rapid drying may cause °checking° or cracking of the lumber and may result in many defects and blemishes that greatly reduce the market value of the product. Particularly in the case of thick material, if the moisture is suddenly entirely dried out of the surface of the, piece while its centre is still moist, the uneven shrinkage that results is bound to show and greatly to impair the value of the piece.
Other equipment of the sawmill plant may include shingle and lath mills that utilize mate rial especially suited for such purposes and also short pieces and other waste from the sawmill in the manufacture of these minor products.
In addition to ample storage yard space in which the lumber of the lower grades is piled and also the stock that is to he air-dried, the plant will usually include storage sheds for the accommodation of a stock of dressed lumber and perhaps moldings, flooring and other prod ucts of the planing mill.