72 inches long is slightly more than 93.72 inches, but93 3/4 inches is close enough for practical purposes.Once you know the total length of the member, justmeasure it off and make the end cuts. To make these cutsat the proper angles, set the square to the unit of run onthe tongue and the unit of rise on the blade and draw aline for the cut along the blade (lower end cut) or thetongue (upper end cut).SCALESA framing square contains four scales: tenths,twelfths, hundredths, and octagon. All are found on theface or along the edges of the square. As we mentionedearlier, the tenths scale is not used in roof framing.Twelfths ScaleFigure 2-8.-Unit length.14.4 inches. For practical purposes, you can round thisto 14 3/8.To lay out the full length of the brace, set the squareto the unit of rise (14 3/8 inches) and the unit of run(12 inches), as shown in figure 2-7. Then, step off thiscut as many times as the unit of run goes into the totalrun (60/12, or 5 times).Determining Line LengthIf you do not go through the stepping-off procedure,you can figure the total length of the member in questionby first determining the bridge measure. The bridgemeasure is the length of the hypotenuse of a righttriangle with the other sides equal to the unit of run andunit of rise. Take the situation shown above in figure 2-7.The unit of run here is 12 inches and the unit of rise is14 3/8 inches. Set the square to this cut, as shown infigure 2-8, and mark the edges of the board as shown. Ifyou measure the distance between the marks, you willfind it is 18 3/4 inches. Bridge measure can also be foundby using the Pythagorean theorem: + = Here,the unit of rise is the altitude (a), the unit or run is thebase (b), and the hypotenuse(c) is the bridge measure.To get the total length of the member, you simplymultiply the bridge measure in inches by the total run infeet. Since that is 5, the total length of the member is18 3/4 x 5, or 93 3/4 inches. Actually, the length of thehypotenuse of a right triangle with the other sides 60 andThe graduations in inches, located on the back ofthe square along the outer edges of the blade and tongue,are called the twelfths scale. The chief purpose of thetwelfths scale is to provide various shortcuts in problemsolving graduated in inches and twelfths of inches.Dimensions in feet and inches can be reduced to 1/12thby simply allowing each graduation on the twelfths scaleto represent 1 inch; for example, 2 6/12 inches on thetwelfths scale may be taken to represent 2 feet 6 inches.A few examples will show you how the twelfths scaleis used.Suppose you want to know the total length of a rafterwith a total run of 10 feet and a total rise of 6 feet5 inches. Set the square on a board with the twelfthsscale on the blade at 10 inches and the twelfths scale onthe tongue at 6 5/12 inches and make the usual marks.If you measure the distance between the marks, you willfind it is 11 11/12 inches. The total length of the rafteris 11 feet 11 inches.Suppose now that you know the unit of run, unit ofrise, and total run of a rafter, and you want to find thetotal rise and the total length. Use the unit of run(12 inches) and unit of rise (8 inches), and total run of8 feet 9 inches. Set the square to the unit of rise on thetongue and unit of run on the blade (fig. 2-9, top view).Then, slide the square to the right until the 8 9/12-inchmark on the blade (representing the total run of 8 feet9 inches) comes even with the edge of the board, asshown in the second view. The figure of 5 10/12 inches,now indicated on the tongue, is one-twelfth of the totalrise. The total rise is, therefore, 5 feet 10 inches. Thedistance between pencil marks (10 7/12 inches) drawnalong the tongue and the blade is one-twelfth of the totallength. The total length is, therefore, 10 feet 7 inches.2-6

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