Pipe tee and lateral template calculator
For a branch whose axis meets the main pipe axis, at 90° or as a lateral: enter both diameters, the lengths and the branch angle. You get the fish mouth cut for the branch and the hole in the main pipe.
Enter your measurements
Seam
1,649.4mm
Exact geometry
- Cut length
- 1,589.6 mm
- Cut curve length
- 326.1 mm
- Sheet size
- 975.0 × 400.0 mm
How to lay it out
Draw the branch stretchout
Draw the branch mouth as a straight line as long as the branch circumference, divide it into equal parts and square a line from each point.
Mark the fish mouth
On each line, mark the cut point at the distance given for that line and join the points in a smooth curve. The seam is on the line in the plane of both pipe axes.
Lay out the main pipe
Draw a rectangle as long as the main pipe and as wide as its circumference. The seam runs along the bottom of the pipe, so the top line is the middle of the sheet.
Mark the hole
Mark each hole point by its distance along the main pipe and its arc distance from the top line, then join the points.
Cut and fit
Cut the hole and the branch. Each point on the branch curve lands on the hole point with the same number.
Good to know
- FabLayout runs the same code as Trueflat; the result is exact geometry.
- Source: No published source. Method: each straight line of the branch is intersected with the main surface and both parts are unrolled, developed on the sheet middle; checked by two independent implementations in Trueflat.
Method and formula
The branch is a round pipe whose axis meets the main pipe axis at the branch angle γ, 90° for a square tee or less for a lateral. Every straight line along the branch is followed down until it touches the main pipe. That point gives one point of the fish mouth on the branch and, unrolled, one point of the hole in the main.
- Branch cut: on the line at angle θ around the branch, the cut lies (r × cos θ × cos γ + √(R² − r² × sin² θ)) ÷ sin γ along the branch axis from the main axis. r and R are the branch and main radii.
- Hole: each cut point is unrolled onto the main pipe as its distance along the pipe and its arc from the top line.
- Seams: the branch seam is on the line at θ = 0, in the plane of both axes; the main seam is on the bottom, so it never crosses the hole.
The pattern is exact. Enter measurements to the middle of the sheet. Which face of the branch seats on the main depends on how you fit and weld it, so this shape is developed on the sheet middle only.
Worked example
Main 200 mm, branch 100 mm, branch length 200 mm, main length 400 mm, foot at 200 mm, 90°: the cut lies √(100² − 50² × sin² θ) from the main axis, so 100 mm on the seam line and 86.60 mm on the line at 90°. The hole runs from 150 to 250 mm along the main pipe and reaches 52.36 mm of arc (30°) to each side of the top line.
Questions
When do I use this page and when the offset or eccentric tee?
Use this page when the branch axis meets the main pipe axis, square or as a lateral down to 20°. If the branch axis passes beside the main axis, use the eccentric tee for a square branch or the offset tee for an angled one.
Can the branch be as large as the main pipe?
Yes, up to the same diameter. A larger branch is rejected because it would be wider than the main pipe.
Why must the curve samples be a multiple of 4?
So that the lines at 90°, 180° and 270° fall on a division point. Those are the turning points of the saddle. Use at least 8.
Do I measure inside, middle or outside?
Enter measurements to the middle of the sheet. Which face of the branch seats on the main depends on how you fit and weld it, so this shape is developed on the sheet middle only.
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