Développeur de Tracé de Réducteur Excentrique & Concentrique

A reducer steps a duct or pipe from one diameter to another. A concentric reducerkeeps both circles on the same centerline, so it shortens evenly all the way around; an eccentric reducer shifts the top circle to one side so that one side of the fitting stays flush and straight - the shape needed at a level floor, a level pipe invert, or anywhere a duct or pipe run cannot be allowed to step up on one side. This tool develops the flat (unrolled) pattern for either case from four inputs, and exports a printable, mirror-matched two-half template.

How to use it: enter the larger (bottom) and smaller (top) diameters, the vertical height between them, and the offset between their centers. Leave offset at 0 for a concentric reducer (both centers aligned), or set it up to bottom radius − top radius for a fully eccentric reducer with one perfectly straight, vertical side - the most common eccentric reducer style.

Method: triangulation, split at the offset axis. Both circles are divided into equal angular steps from the near seam (nearest the offset direction) to the far seam (180° around), and the two open arcs are triangulated with the same minimum-diagonal method used for the square-to-round developer, then unrolled using true 3D edge lengths. Because the shape is symmetric about the offset axis, the second half is an exact mirror of the first - only one half needs to be computed.

Worked check. With the defaults (250 mm bottom, 150 mm top, 200 mm height): bottom radius 125 mm − top radius 75 mm = 50 mm, which is exactly the entered offset - so this is a fully flush reducer, and the near side comes out to exactly the height, 200 mm (the shortest a straight side can be between the two planes). The far side is longer, at ≈ 223.6 mm. Lower the offset toward 0 and both sides converge to the concentric value, ≈ 206.2 mm, matching the cone flat pattern tool for the same non-offset dimensions.

Reading the result. Near-side and far-side lengths are the two straight generatrices at the seam ends of each half - use them to check the template against a tape measure before cutting. "Fully flush" confirms the near side landed exactly vertical (offset = bottom radius − top radius); if it reads "No" with a nonzero offset, the fitting is eccentric but one side will still slope slightly, which is expected for any offset short of the maximum.

Le résultat ci-dessus utilise exactement ces valeurs. Cet instantané est inclus à l’impression pour comparer la sortie aux mesures d’origine.

Larger (bottom) diameter

250 mm

Smaller (top) diameter

150 mm

Vertical height

200 mm

Offset

50 mm

Development lines per half

6

Résultat principal: Near (short) side length: 200.0 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 is a triangulated approximation, standard for eccentric reducer layout. The near seam (where both halves share the same seed edge) is exact; a very small gap or overlap can accumulate by the far seam for a strongly eccentric, low-line-count pattern - increase development lines to tighten it, and true up the seam by eye when fitting.

The pattern is the bare developed geometry only - add seam allowance, hem or lap separately, on the outside of the printed outline, before cutting.