rafter line length may be found either by calculation

foot. The answer is 14 5/12 times 10 = 144 2/12

or by use of the steel square.

inches, or 12 feet and 2/12 inches. The amount of

overhang must be added if an overhang is to be used

(it is often 1 foot). Dropping the fraction, this makes

forms the hypotenuse of a right triangle whose other

a total of 13 feet for the length of the rafter.

sides are the total rise and the total run (fig. 2-13). It

can therefore be determined by the following

formula:

determined, the timber is laid on sawhorses,

sometimes called "saw benches", with the crown or

bow (if any) as the top side of the rafter. Select the

straightest piece possible for the pattern rafter. If a

straight piece is not available, place the crown toward

the person laying off the rafter. Hold the square with

the tongue in the right hand, the blade in the left, and

the heel away from the body, and place the square as

near the upper end of the rafter as possible. In this

case, the figures 8 on the tongue and 12 on the blade

are placed along the edge of timber which is to be the

top edge of the rafter as shown in 1, figure 2-14.

Mark along the tongue edge of the square, which will

be the plumb cut at the ridge. Since the length of the

rafter is known to be 12 feet, measure that distance

from the top of the plumb cut and mark it on the

timber. Hold the square in the same manner with the

8 mark of the tongue directly over the 12-foot mark.

Mark along the tongue of the square to give the

plumb cut for the seat (2, fig. 2-14). Next measure

off, perpendicular to this mark, the length of

overhang along the timber and mark a plumb-cut

mark in the same manner, keeping the square on the

same edge of the timer (3, fig. 2-14). This will be the

tail cut of the rafter. Sometimes the tail cut is made

square across the timber.

the width of the plate, measured perpendicular to the

plumb cut, as shown in 4, figure 2-14. Using the

square, square lines down on the sides from all level

and plumb-cut lines. Now the rafter is ready to be

total run and the rise in inches. Assume that you

cut (5, fig. 2-14).

have determined a run of 10 feet and a rise of 8

inches per foot of run. To determine the approximate

building is 20 feet, 8 inches wide, the run of the rafter

line length of rafter, measure on the steel carpenter

would be 10 feet, 4 inches, or half the span. Instead

square the distance between 8 on the tongue and 12

of using the method in **a **above, the rafter length may

on the blade, because 8 is the rise and 12 is the unit

be determined by "stepping it off" by successive

of run. This distance is 14 5/12 inches, and

steps with the square as shown in figure 2-15. Take

represents the line length of a rafter with a total run

the

of 1 foot and a rise of 8 inches. Since the run of the

rafter is 10 feet, multiply 10 by the line length for 1

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