This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
Lumber may be found in lumber yards in certain shapes ready for use, having been cut from the logs and relieved of their outside covering of bark. The cutting up of the logs is done in the mills by machinery and there are various methods in use for transforming the logs into boards, planks, and heavy timbers. The method of cutting the log determines the appearance of the wood when finished and also affects it in other ways.
Fig. 11. Economical Method of Cutting Logs.
Fig. 12. Another Method of Cutting Logs.
If the log is to be squared off so as to form only one heavy beam or post, a good rule to follow is to divide the diameter into three equal parts and then to draw perpendiculars to this diameter at the division points one on each side of the center, as shown at A and B in Fig. 11. The points C and D in which these perpendiculars to the diameter cut the circumference of the log, together with the points E and F in which the diameter cuts the circumference of the log, will be the four corners of the timber. The lines joining these points will give an outline of the timber, which will be rectangular and will be found to be the largest and best timber which can be cut from the log. Another good rule is to divide the diameter of the log into four equal parts and to proceed in the same way as described above, using the outside quarter points from which to draw the perpendiculars as shown in Fig. 12. This method will give the outlines of a stiffer beam than the one described above, but there will be more waste from the log and the beam will not be on the whole as strong as the other.
In Fig. 13 are shown several different methods of cutting planks from a log. First it is divided into quarters, and the planks are cut out as shown in the figure, there being four ways in which the work may be done. All of the four methods shown may be said to give what is called quarter-sawed lumber since the log is first cut into quarters, but that shown at A is the best. All of the planks are cut radiating from the center of the log and there will be no splitting or warping, but the method is very expensive, as all of the planks have to be squared up afterward and there is much waste as a result. A fairly good method is that shown at B where the planks are nearly along radial lines and may be much more easily and cheaply cut out than can those shown at A. The method shown at C is a common one and leads to fairly good results, although only the plank nearest the center is on a radial line. It is practically as good a method as that shown at B and is much more simple. The method shown at D is not so good as the others, as planks cut out in this way are very liable to warp and twist. If the silver grain, caused by cutting of the medullary rays is desired, the planks must be cut as shown at A, B, or C.
Fig. 13. Method of Cutting Planks from a Log.
Planks are sometimes simply sliced from the log as shown in Fig. 14, without first dividing it into quarters, but this is the worst possible way of cutting them, as the natural tendency of the timber to shrink causes the planks to curl up as shown in Fig. 15. It is almost impossible to flatten them out again, and they can not be used in that condition.
There is another method of cutting up a log which has been introduced more recently than the others, and which is known as the "rotary cut." It consists in placing the log on a movable carriage which keeps it whirling rapidly about its longitudinal axis, at the same time bringing it up against a long stationary knife which catches the log and peels off strips around the circumference of any desired thickness. This method is used extensively in the preparation of wood to be used as veneers, and in the case of many kinds of wood the figure is brought out to better advantage in this way than is possible with any other method.