Développeur de Patron de Coude Segmenté (Dos de Homard)

How to use it: enter the pipe or duct diameter, the centerline radius of the overall bend you want, the total elbow angle (90° for a standard elbow), and how many straight pieces to build it from. More pieces give a smoother-looking bend and less flow resistance, at the cost of more cutting and welding/seaming.

Method: tangent-line construction. The bend's centerline arc is approximated by straight pieces tangent to it, changing direction at each joint. This gives the standard result: cut angle per joint = total angle ÷ (2 × (pieces − 1)) - the same angle at every joint. End pieces get one angled cut (mating to straight pipe on the square end); every middle piece gets two opposing cuts.

Flat pattern. A cylinder sliced by a plane tilted at the joint angle unrolls into a cosine curve - long on the outside of the bend, short on the inside, with amplitude = pipe radius × tan(joint angle). All middle pieces are geometrically identical, as are both end pieces, so the diagram shows one of each: cut the quantities noted below it.

The result above uses these exact values. This snapshot is included when the page is printed so the output can be checked against the original measurements.

Pipe/duct diameter

200 mm

Bend centerline radius

400 mm

Total elbow angle

90 deg

Number of pieces

4

Primary result: Miter (cut) angle per joint: 15.00 deg.

• Measure from the datum or reference edge described by this tool, and do not mix inside, outside and centerline dimensions.
• Keep inputs in the displayed units and preserve more precision than the final cutting or purchasing tolerance requires.
• When the result is close to a limit, verify it with a test piece, field measurement, manufacturer drawing or qualified project professional.

If the short (inside) length of a piece would come out at zero or below, the combination of diameter, bend radius, angle and piece count is not physically buildable - the calculator returns no result in that case. Increase the bend radius, reduce the angle, or add more pieces.

The pattern is the bare developed geometry only - add seam allowance for a welded or lock-seamed joint separately, on the outside of the printed outline.