Tee on a segmented elbow calculator
For a square branch set into one piece of a segmented (lobster back) elbow: enter the elbow, the pierced piece, the side and the branch. You get every elbow piece, the hole in the pierced piece and the branch cut.
Enter your measurements
Seam
5,332.7mm
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
Lay out the elbow pieces
Lay out each piece as for a segmented elbow: stretchout, equal divisions and the miter curves, with the seam on the throat.
Find the branch centre on the pierced piece
On the pierced piece, measure the branch foot position along the piece axis from the start of the piece, on the line at the branch angle around the pipe.
Mark the hole
Mark each hole point by its arc distance from the seam and its distance along the piece, and join the points.
Lay out the branch
Draw the branch stretchout, square a line from each division and mark each cut point at its distance from the drawing.
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 main part is a segmented elbow, laid out as on the lobster back elbow page. The branch is a round pipe square to the axis of one piece, the pierced piece. Inside that piece the elbow is a plain cylinder, so the branch is cut as for a pipe tee on that piece.
- Branch position: the foot position is measured along the piece axis from the start of the piece. The angle around the pipe is 0° at the throat and 180° at the back.
- Branch cut: as for an eccentric tee on a pipe of the elbow diameter.
- Hole: drawn on the pierced piece's own pattern, at arc r × (θb − φ) from the seam and at its distance along the piece, where r is the elbow pipe radius, θb the branch angle around the pipe and φ the angle of the hole point.
The hole must stay at least 5 mm from both miter curves, and the branch angle around the pipe must be between 90° and 270°. 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
Elbow 200 mm, bend radius 300 mm, 90°, 4 pieces; branch 80 mm, 250 mm long, on piece 1 at 180°. Piece 1 is 160.77 mm long on the axis, so its middle is at 80.38 mm. The hole is centred on the back line, 314.16 mm from the seam, and runs from 40.38 to 120.38 mm along the piece. At the side lines the branch cut is √(100² − 40²) = 91.65 mm from the piece axis. The hole stays 67.18 mm clear of the miter curves.
Questions
How are the pieces counted?
From 0 at the first end piece. In a 4-piece elbow, pieces 0 and 3 are the end pieces and pieces 1 and 2 are the middle pieces. The default, piece 1, is the first middle piece.
Can the branch sit across a miter?
No. The hole must stay inside one piece, at least 5 mm from both miter curves. Move the branch foot toward the middle of the piece or use a smaller branch.
Can I put the branch on the throat side?
Not in this version. The angle around the pipe must be between 90° and 270°, from the side to the back of the elbow.
How is this different from the branch joined with two elbows?
Here the elbow is the main part and a straight branch goes into it. On the two-elbow page the main is a straight pipe and the branches are elbows.
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