Figure 3-47. - Finding the cutback.
distance along the bottom quarter line. Make punch marks with the center punch on each side of the line, along the side quarter lines. These marks will make it easy to align the pipe for welding after the joint is cut. Use the spring steel wraparound and pull the loop to the cutback point. Next, draw a chalk line over the top half of the pipe through the first cutback point. (NOTE: Do not allow the wraparound to twist or kink, and hold the chalk at a right angle to the wraparound while marking the pipe.) Now roll the pipe one-half turn and mark a chalk line in the same way around the bottom half of the pipe.
If a template is not available, you may determine the dimensions and markings for the cut necessary for a two-piece welded turn of any angle between 1 degree and 90 degrees by making a full-sized drawing, as shown in figure 3-48.
Draw the center lines intersecting at b by using the angle of turn T and then draw the outlines of the pipes by using the center lines and the diameter D. These will intersect at a and c. By laying the pipe over the drawing so that point b will coincide with that determined by construction details, you can draw the lines a-b and c-b in preparation for miter cutting and beveling.
After being prepared for welding, one section of pipe should be rotated through 180 degrees to form the desired angle, and then it should be tack-welded.
Figure 3-48. - To locate cut on a pipe for any angle two-piece turn.
Spacing should be slightly greater at the inside of the turn.
To lay out the template for cutting the branch and header for a 90-degree tee with header and branch of equal diameter, draw the side and end view, as shown in figure 3-49, views A and B.
In making the template for the branch in figure 3-49, view A, draw lines 1-5 at 45 degrees to the center line. Lay off distance 1-P equal to twice the thickness of the pipe wall and draw the smooth curve s-P-s. Now, project point P from view A to view B and draw the lines P-t radially. At a distance above point t equal to the thickness of the header wall, draw a-t horizontally, and vertical lines a-a and t-t. With lower points a as center, swing arcs r-s. Using the intersections of these arcs as centers and with the same radius, draw the curved lines a-be-d-e arid e d-c-b-a.
Divide the outside circumference of the branch top into equal parts and draw the vertical lines b-b, c-c, and so forth. Also, draw the horizontal base line a-a.
Lay off the unwrapped circumference (fig. 3-49, view D), and divide each half of it into the same number of equal parts as the branch semicircumference. In view D, you should plot the distances a-a, b-b, and so forth, from view B. This gives the distances from the base line to the branch curve of the intersection and determines the location of the branch template.Continue Reading