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Steelworker Volume 02 - Building manual for how to work with steel | Next
Circumference Rule |
Imagine that you have line XY with A as a point
at which you need to fabricate a perpendicular to form
a right angle. Select any convenient point that lies
somewhere within the proposed 90-degree angle. In
figure 2-9 that point is C. Using C as the center of a
circle with a radius equal to CA, scribe a semicircular
arc, as shown in figure 2-9. Lay a straightedge along
points B and C and draw a line that will intersect the
other end of the arc at D. Next, draw a line connecting
the points D and A and you have fabricated a
90-degree angle. This procedure may be used to form
90-degree comers in stretch-outs that are square or
rectangular, like a drip pan or a box.
Laying out a drip pan with a pair of dividers is no
more difficult than fabricating a perpendicular. You
will need dividers, a scriber, a straightedge, and a sheet
of template paper. You have the dimensions of the pan
to be fabricated: the length, the width, and the height
or depth. Draw a base line (fig. 2-10). Select a point
on this line for one comer of the drip pan layout. Erect
a perpendicular through this point, forming a
90-degree angle. Next, measure off on the base line
the required length of the pan. At this point, erect
another perpendicular. You now have three sides of the
stretch-out. Using the required width of the pan for the
other dimensions, draw the fourth side parallel to the
base line, connecting the two perpendiculars that you
have fabricated.
Now, set the dividers for marking off the depth of
the drip pan. You can use a steel scale to measure off
the correct radius on the dividers. Using each comer
for a point, swing a wide arc, like the one shown in the
second step in figure 2-10. Extend the end and side
lines as shown in the last step in figure 2-10 and
complete the stretch-out by connecting the arcs with a
scriber and straightedge.
Bisecting an arc is another geometric construction
that you should be familiar with. Angle ABC (fig.
2-11) is given. With B as a center, draw an arc cutting
the sides of the angle at D and E. With D and E as
centers and a radius greater than half of arc DE, draw
arcs intersecting at F. A line drawn from B through
point F bisects angle ABC.
Two methods used to divide a line into a given
number of equal parts are shown in figure 2-12. When
the method shown in view A is to be used, you will
need a straightedge and dividers. In using this method,
draw line AB to the desired length. With the dividers
set at any given radius, use point A as center and scribe
an arc above the line. Using the same radius and B as
center, scribe an arc below the line as shown. From
Figure 2-10.—Laying out a drip pan with dividers.
Figure 2-11.—Bisecting an arc.
2-4
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