Offset lateral template calculator
For an angled branch whose axis passes beside the main pipe axis: enter both diameters, the offset and the branch angle. You get the branch cut and the hole. With no offset, the pipe tee page is simpler.
Enter your measurements
Seam
2,558.8mm
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, starting at the seam.
Mark the cut on each line
Mark each cut point at its own distance from the drawing. The curve is lopsided, so keep the line order from the seam.
Lay out the main pipe
Draw a rectangle as long as the main pipe and as wide as its circumference, with the seam along the bottom of the pipe.
Mark the hole off the top line
Mark each hole point by its distance along the pipe and its arc from the top line. With an offset, the hole sits more on one side of that line.
Join and cut
Join the points of the branch and of the hole in smooth curves and cut both.
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
This is the general round tee: the branch is both tilted to the main pipe, by the branch angle γ, and moved sideways, by the offset e. The offset is the shortest distance between the two axes.
- Side position of the branch line at angle θ: y = e + r × sin θ.
- Cut: that line meets the main pipe (r × cos θ × cos γ + √(R² − y²)) ÷ sin γ along the branch axis from the foot.
- Hole: each cut point is unrolled onto the main pipe as its distance along the pipe and its arc from the top line.
Because of the offset, the cut and the hole are no longer the same on both sides of the branch. The offset plus half the branch diameter may not exceed half the main diameter: past that, part of the branch misses the main pipe. A negative offset gives the mirror image. 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 300 mm, 800 mm long, foot at 400 mm, branch 100 mm, 300 mm long, angle 60°, offset 60 mm. Along the branch axis, the cut lies 187.61, 117.76, 129.88 and 172.82 mm from the foot on the lines at 0°, 90°, 180° and 270°. The shortest branch line is 106.51 mm.
Questions
How is the offset tee different from the eccentric tee and the pipe tee?
The pipe tee has an angle but no offset. The eccentric tee has an offset but is always square. The offset tee has both, so use it for a lateral that also sits off-centre.
What is the offset measured to?
The shortest distance between the two axes, measured square to both of them. Zero means the axes meet.
Why does it say the branch does not meet the main all the way round?
The offset plus half the branch diameter is more than half the main diameter, so one side of the branch passes the main pipe. Reduce the offset or the branch diameter. Exactly equal is allowed: the branch is then flush with the side of the main.
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