Part 13 (1/2)

For measuring distances, the _rule_, Fig. 191, is the one in most common use. It is usually made of boxwood. For convenience it is hinged so as to fold. A rule is called ”two-fold” when it is made of two pieces, ”four-fold” when made of four pieces, etc. When measuring or marking from it, it can be used more accurately by turning it on edge, so that the lines of the graduations may come directly against the work. The one in most common use in school shops, is a two-foot, two-fold rule. Some instructors prefer to have pupils use a four-fold rule, because that is the form commonly used in the woodworking trades. Steel bench-rules, Fig. 192, are satisfactory in school work because unbreakable and because they do not disappear so rapidly as pocket rules. They need to be burnished occasionally.

[Ill.u.s.tration: Fig. 191. Two-Foot Rule. Two Fold.]

[Ill.u.s.tration: Fig. 192. Steel Bench-Rule.]

[Ill.u.s.tration: Fig. 193. Back of Steel Square, Brace Measure.]

The _steel square_, Figs. 193, 194, 196, 197, is useful, not only as a straight-edge and try-square, but also for a number of graduations and tables which are stamped on it. There are various forms, but the one in most common use consists of a blade or ”body” 24”2” and a ”tongue,” 16”1-1/2”, at right angles to each other. Sargent's trade number for this form is 100. It includes graduations in hundredths, thirty-seconds, sixteenths, twelfths, tenths, and eighths of an inch, also a brace-measure, an eight-square measure, and the Ess.e.x board-measure. Another style, instead of an Ess.e.x board-measure, and the hundredths graduation has a rafter-table. The side upon which the name of the maker is stamped, is called the ”face,” and the reverse side the ”back.”

The brace-measure is to be found along the center of the back of the tongue, Fig. 193. It is used thus: the two equal numbers set one above the other represent the sides of a square, and the single number to their right, represents in inches and decimals, the diagonal of that square. E. g., 54/54 76.37 means that a square the sides of which are 54” would have a diagonal of 76.37”.

For determining the length of the long side (hypothenuse) of a right angle triangle, when the other two given sides are not equal, the foot rule, or another steel square may be laid diagonally across the blade and arm, and applied directly to the proper graduations thereon, and the distance between them measured on the rule. If the distance to be measured is in feet, use the 1/12” graduations on the back of the square.

[Ill.u.s.tration: Fig. 194. Face of Steel Square, Octagon, ”Eight-Square,” Scale.]

To use the octagonal (or 8-square) scale, Fig. 194, which is along the center of the face of the tongue, with the dividers, take the number of s.p.a.ces in the scale to correspond with the number of inches the piece of wood is square, and lay this distance off from the center point, on each edge of the board. Connect the points thus obtained, diagonally across the corners, and a nearly exact octagon will be had.

E.g., on a board 12” square, Fig. 195, find A.B.C.D., the centers of each edge. Now with the dividers take 12 s.p.a.ces from the 8-square scale. Lay off this distance on each side as A' A” from A, B' B” from B, etc. Now connect A” with B', B” with C', C” with D', D” with A', and the octagon is obtained.

[Ill.u.s.tration: Fig. 195. Method of Using the Eight-Square Scale on the Steel-Square.]

In making a square piece of timber octagonal, the same method is used on the b.u.t.t, sawed true. When the distance from one center is laid off, the marking-gage may be set to the distance from the point thus obtained to the corner of the timber, and the piece gaged from all four corners both ways. Cutting off the outside arrises to the gaged lines leaves an octagonal stick.

[Ill.u.s.tration: Fig. 196. Back of Steel Square, Ess.e.x Board Measure.]

The board-measure is stamped on the back of the blade of the square, Fig. 196. The figure 12 on the outer edge of the blade is the starting point for all calculations. It represents a 1” board, 12” wide, and the smaller figures under it indicate the length of boards in feet.

Thus a board 12” wide, and 8' long measures 8 square feet and so on down the column. To use it, for boards other than 12” wide:--find the length of the board in feet, under the 12” marked on the outer edge of the blade, then run right or left along that line to the width of the board in inches. The number under the width in inches on the line showing the length in feet, gives the board feet for lumber 1” thick.

For example, to measure a board 14' long, and 11” wide,--under the figure 12, find 14 (length of the board); to the left of this, under 11 is the number 12.10; 12' 10” is the board-measure of the board in question. Since a board 12' long would have as many board feet in it as it is inches wide, the B. M. is omitted for 12' boards. Likewise a board 6' long would have 1/2 the number of board feet that it is inches wide. If the board is shorter than the lowest figure given (8) it can be found by dividing its double by 2.; e. g., to measure a board 5' long and 9” wide, take 10 under the 12, run to the left of the number under 9, which is 7' 6”: 1/2 of this would be 3' 9”, the number of board feet in the board.

If the board to be measured is longer than any figure given, divide the length into two parts and add the result of the two parts obtained separately. For example, for a board 23' long and 13” wide,--take 12'13” = 13'; add to it, 11'13” = 11' 11”; total, 24'11”.

[Ill.u.s.tration: Fig. 197. Steel Square with Rafter Table.]

A good general rule is to think first whether or not the problem can be done in one's head without the a.s.sistance of the square.

The table is made, as its name, Board-Measure (B. M.) implies, for measuring boards, which are commonly 1” thick. For materials more than 1” thick, multiply the B. M. of one surface by the number of inches thick the piece measures.

The rafter-table is found on the back of the body of the square, Fig.

197. Auxiliary to it are the twelfth inch graduations, on the outside edges, which may represent either feet or inches.

[Ill.u.s.tration: Fig. 198. The ”Run” and ”Rise” of a Rafter.]

By the ”run” of the rafter is meant the horizontal distance when it is set in place from the end of its foot to a plumb line from the ridge end, i. e., one half the length of the building, Fig. 198. By the ”rise” of the rafter is meant the perpendicular distance from the ridge end to the level of the foot of the rafter. By the pitch is meant the ratio of the rise to twice the run, i. e., to the total width of the building. In a 1/2 pitch, the rise equals the run, or 1/2 the width of the building; in a 1/3 pitch the rise is 1/3 the width of the building; in a 3/4 pitch the rise is 3/4 the width of the building.

[Ill.u.s.tration: Fig. 199. Lumberman's Board Rule.]

To find the length of a rafter by the use of the table, first find the required pitch, at the left end of the table. Opposite this and under the graduation on the edge representing the run in feet, will be found the length of the rafter; e.g., a rafter having a run of 12' with a 1/4 pitch, is 13' 5” long, one with a run of 11' and a 1/3 pitch, is 13' 2-8/12”, one with a run of 7' and a 5/8 pitch, is 11' 2-6/12”

long, etc.

When the run is in inches, the readings are for 1/12 of the run in feet: e.g., a rafter with a run of 12” and a 1/4 pitch is 13-5/12”, one with a run of 11” and a 1/3 pitch, is 13-3/12”. Where the run is in both feet and inches, find the feet and the inches separately; and add together; e.g., a rafter with a run of 11' 6”, and a 1/2 pitch, is 15' 6-8/12” + 8-6/12” = 16' 3-2/12”.