Sawed lumber, like joists, plank, and scantlings, are now bought and sold by board measure. Hence, to measure them, Multiply the width in inches by the thickness in inches; multiply the product by the length in feet, and divide by 12. Thus, a plank 12 feet long, 2 feet wide, and 3 inches thick, would contain 24 × 3 × 12 12 =72 feet. The number of feet, board measure, which can be sawn from a given log, can be only approximately determined from general tables. The following is the standard commonly adopted for logs 10 feet in length and of the diameters indicated, measured under the bark at the smaller end. To find the contents in board measure of a log of any length, look for its diameter in the table, take the corresponding number of feet, point off one place, and multiply by the length of the log. In measuring boards, it is often better to consider the width in inches as the fraction of a foot. Thus, for a board 18 feet long and 8 inches wide, 18 x 8 we may reckon directly 18 x = instead of 12 feet. 12 So a plank 16 feet long, 3 inches thick, and 6 inches wide, may be reckoned 16 × 1 × 3 = 24 feet. Suppose the question be, How many boards, 12 ft. long and 8 in. wide, will be required for a close fence 4 ft. high and 100 ft. long. Here the number of sq. ft. required is 4×100, and the contents of each board, 12 × . Hence, the number required is 400=50. Or, required the number of feet of plank in a pile of 24 rows, 16 in each row, each plank being 16 ft. long, 2 in. thick, and 8 in. wide. How Solve it thus: 24 x 16 x 16 x 2x=8192. many logs, 15 ft. long and 19 in. diameter, will be required to make 50,000 ft. of boards? From the table, each log will make 14 × 15=210 ft. Hence, the number required is 98=238, nearly. 5000 ROUND TIMBER AND SQUARE TIMBER. Round Timber and Square timber are bought and sold by the cubic foot. Several rules are used for determining the number of cubic feet in round logs, disagreeing as to the allowance to be made for waste in hewing. The following is probably most nearly accurate, and most generally used. Square one-third of the sum of the greatest and the least diameters in inches, multiply by the length of the log in feet, and divide by 144. Thus a log 12 feet long, 2 feet in diameter at one end, and 15 inches at the other, would contain (24+16) x=141 ft. 2 In the following table the number of cubic feet is given for logs 10 feet long and of the average diameter indicated: To find the contents, in cubic measure, of a log of any length, look for its average diameter, take the corresponding number of feet, point off one place, and multiply by the length of the log. To find the contents of Square timber, multiply the width in inches by the thickness in inches, and the product by the length in feet; then divide by 144. As in board measure, it is usually better to calculate the breadth and thickness as fractions of a foot, and thus avoid division by 144. Thus, a beam 20 ft. long, 9 in. wide, and 9 in. thick, contains 20xx=114 ft. To get the entire cubic contents of a round log, multiply the square of the circumference at the middle of the log by 8 times the length, and divide 100. This short rule gives a result differing hardly a half of one one-hundredth from the precise amount. Spars from 4 to 10 inches in diameter are estimated according to their diameter inside the bark, at one-third of their length from the larger end. They should be about 5 ft. in length for every foot in diameter. The side of a square inscribed in a circle equals its diameter multiplied by .707106. Hence, the side of the largest square piece of timber which can be hewn from a given log, will be, or about of the diameter at the smaller end. Hence, to get out square timber of a certain thickness, the logs should be three-halves that thickness in diameter, at the smaller end. Thus, a log 10 in. in least diameter would, if straight, give square timber, 7 in. wide and 7 in. thick. To get out a beam 8 in. square, a log should be taken 12 in. in least diameter. |