This page explains creation of a pipe cutting template (cut back for branch pipe and hole template for header pipe). For explanation, we will consider header pipe of size 10″ Sch 40 and branch of size 6 “. Lets consider angle of lateral to be 45 degrees.
For stub in type branch, we have to consider ID of header and OD or branch. So the input data is as follows:
- Header pipe ID : 273 mm – (2 *9.27mm) = 255.46 i.e. 255 mm approx.
- Branch Pipe OD : 168.3 mm i.e. 168 mm approx.
First draw a box of length more than 3 times header dia and height of exactly OD of header pipe. Here we have a box of length 1000 mm and height 255 mm (OD of header). Also draw horizontal and vertical center lines for header pipe.
Next draw two half circles of Branch OD diameter (168 mm) on left side and Header ID diameter (255 mm) on right side as shown in blue color. Centers of these circles shall be on left and right edges of header pipe respectively.
Divide Left half circle of Branch OD into 8 parts of 22.5 degree each as shown below. Number them as shown in figure.
Draw quarter circle with radius of Branch OD at the top aligned with right edge of header pipe as shown in magenta color. Divide this circle in 4 equal parts of 22.5 degrees. Number them as shown.
Draw one line of length equal to OD of branch pipe (168 mm) near middle of header pipe and starting from top edge (as shown by magenta color below) at branch angle (45 Degree in this case). Draw half circle of branch OD radius and divide it into 8 equal parts of 22.5 degree each. Number them as shown below.
Draw vertical lines from points 1 to 4 and intersect with them with half circle of header OD as shown below, on right edge of pipe header. Mark intersections as A,B,C,D as shown below with red dots.
Draw extension lines at 45 degree (Branch Angle) as shown towards the middle of header.
Draw horizontal lines from intersection points A,B,C and D towards left side as shown. Mark intersection of these lines with lines drawn in step 7 above. Mark same number lines as intersections with red dot. Connect these lines with a curve to get branch pipe cut back profile. Connect A to 1, B to 2 (two dots), C to 3 (two dots), D to 4 (two dots) and top line to 5 (two dots).
Mark horizontal lines from left edge branch OD half circle division points towards right direction as shown, then mark vertical lines from intersection points marked in above step 8, mark intersections of same number lines and draw a curve as shown with thick green line below. This curve is a template for hole to be cut in header pipe.
Calculate outside circumference of branch pipe with the formula Pi * OD i.e. 3.141 * 168 = 528 mm. Draw a horizontal line of this length. Divide this line into 16 equal parts as we have divided header and branch pipes into 16 equal parts of 22.5 degree each. (Length of each part = 528/16 = 33 mm) Number these divisions as shown below. Then draw vertical lines of length equal to distance between marked points 1 to 5 and intersection points marked in step 8. These distances are marked as thick black lines in figure below. Thus we get cut back profile for branch pipe.