Eccentric pipe tee template calculator
For a square (90°) branch set off-centre on a main pipe, as far as flush with its side: enter both diameters and the offset. You get the branch cut and the hole. For an angled off-centre branch, use the offset lateral.
Enter your measurements
Seam
1,671.8mm
Exact geometry
- Cut length
- In the app
- Cut curve length
- In the app
- Sheet size
- In the app
Every result is in Trueflat
The free web version shows the main result and the drawing. Trueflat gives you every mark and measurement, and exports a cut sheet. It is free to download.
How to lay it out
Draw the branch stretchout
Draw the branch mouth line as long as the branch circumference, divide it into equal parts and square a line from each point.
Mark the cut heights
On each line, mark the cut point at the distance from the main axis given in the drawing, then join the points.
Lay out the main pipe
Draw a rectangle as long as the main pipe and as wide as its circumference. The seam is on the bottom of the pipe.
Mark the hole
Mark each hole point by its distance along the pipe and its arc from the top line. With the offset, the hole sits to one side of that line.
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 stands square to the main pipe but its axis is moved sideways by the offset e. Each branch line at angle θ around the branch sits y = e + r × sin θ from the centre plane of the main pipe and meets the main pipe at a height of √(R² − y²) above the main axis. r and R are the branch and main radii.
- Branch: the cut height on each line is √(R² − (e + r × sin θ)²); the mouth is a straight line at the branch length.
- Hole: each cut point is unrolled onto the main as its distance along the pipe and its arc from the top line.
- Tangent tee: when e + r = R, one side of the branch is flush with the side of the main. The cut there comes down to the level of the main axis.
When e + r is more than R, part of the branch misses the main pipe and the shape is rejected. 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
Tangent tee: main 200 mm, branch 100 mm, offset 50 mm. The cut is 86.60 mm above the main axis on the seam line, 0 on the line at 90° (flush side) and 100 mm on the line at 270°. In the hole, the point at 90° sits at the side of the main pipe, 157.08 mm of arc from the top line. With an offset of 60 mm the branch would miss the main by 10 mm.
Questions
When do I use the eccentric tee rather than the pipe tee or offset lateral?
Use the eccentric tee when the branch is square to the main pipe but off its centre line, for example flush with one side. If the branch is centred, use the pipe tee. If it is off-centre and at an angle, use the offset lateral.
What is a tangent tee?
An eccentric tee where the branch side lines up with the side of the main pipe: offset plus half the branch diameter equals half the main diameter. It is the largest offset the calculator accepts.
Why is the cut curve not symmetrical?
The two sides of the branch sit at different distances from the centre of the main pipe, so they meet the curved wall at different heights.
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