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.Continue Reading