Figure 2-9.-Finding total rise and length when unit of run, unit
of rise, and total run are known.
The twelfths scale may also be used to determine
dimensions by inspection for proportional reductions or
enlargements. Suppose you have a panel 10 feet 9 inches
long by 7 feet wide. You want to cut a panel 7 feet long
with the same proportions. Set the square, as shown in
figure 2-9, but with the blade at 10 9/12 inches and the
tongue at 7 inches. Then slide the blade to 7 inches and
read the figure indicted on the tongue, which will be
4 7/12 inches if done correctly. The smaller panel should
then be 4 feet 7 inches wide.
The hundredths scale is on the back of the tongue,
in the comer of the square, near the brace table. This
scale is called the hundredths scale because 1 inch is
divided into 100 parts. The longer lines indicate
25 hundredths, whereas the next shorter lines indicate
5 hundredths, and so forth. By using dividers, you can
easily obtain a fraction of an inch.
The inch is graduated in sixteenths and located
below the hundredths scale. Therefore, the conversion
from hundredths to sixteenths can be made at a glance
without the use of dividers. This can be a great help
when determining rafter lengths, using the figures of the
rafter tables where hundredths are given.
Figure 2-10.Using the octagon square.
The octagon scale (sometimes called the
square scale) is located in the middle of the face of the
tongue. The octagon scale is used to lay out an octagon
(eight-sided figure) in a square of given even-inch
Lets say you want to cut an 8-inch octagonal piece
for a stair newel. First, square the stock to 8 by 8 inches
and smooth the end section. Then, draw crossed center
lines on the end section, as shown in figure 2-10. Next,
set a pair of dividers to the distance from the first to the
eighth dot on the octagon scale, and layoff this distance
on either side of the centerline on the four slanting sides
of the octagon. This distance equals one-half the length
of a side of the octagon.
When you use the octagon scale, set one leg of the
dividers on the first dot and the other leg on the dot
whose number corresponds to the width in inches of the
square from which you are cutting the piece.
FRAMING SQUARE TABLES
There are three tables on the framing square: the unit
length rafter table, located on the face of the blade; the