Kanaal Rolverspringing Fabricage Layout

Why a rolled offset is different. A same-plane offset moves the duct sideways or up in a single direction, and both elbows can be cut and oriented with the cut's long point facing straight up. A rolled offset moves the run in two directions at once (rise and roll), so the true offset is the diagonal between them, and - critically - the miter cut has to be rotated around the duct's own circumference to point along that diagonal. Skipping that rotation is the most common way a rolled-offset fitting comes out misaligned.

Calculation. True offset = √(rise² + roll²). Roll angle (how far to rotate the cut from the rise direction) = atan(roll ÷ rise). Travel = true offset ÷ sin(elbow angle). Advance = true offset ÷ tan(elbow angle). Each elbow's cut angle (from square) is half the chosen elbow angle, using the same tilted-cylinder unroll as the segmented elbow tool.

Worked example. With the defaults (300 mm rise, 400 mm roll - a 3-4-5 triangle), the true offset is exactly 500 mm and the roll angle is 53.1° from the rise direction. At a 45° elbow angle, travel is ≈ 707 mm and advance is exactly 500 mm.

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.

Rise

300 mm

Roll (set)

400 mm

Duct/pipe diameter

200 mm

Elbow angle

45 deg

Primary result: True offset: 500.0 mm.

• 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.

This lays out the two elbow cuts only; it does not size straight duct lengths beyond travel and advance, or account for duct wall thickness, liner, or flange allowances - add those separately.

For a rectangular duct, the miter cut is a straight angled line across the duct rather than the curved profile shown here (which applies to round pipe/duct); the roll angle and cut angle numbers still apply, but you won't need the printable template.