Rectangular Duct: flat pattern
A straight length of rectangular duct: one blank wrapped round to one seam, two L-shaped pieces, a U and a flat side, or four sides. A straight length of rectangular duct folded from sheet: in one piece wrapped round to one seam, in two L-shaped pieces, as a U and a flat side, or as four flat sides.
Open the rectangular duct in SheetMorphConfigurations
- Straight length. A straight length of duct, the same size from end to end.
A worked example
The straight length configuration with the sizes SheetMorph opens with, in mm. One blank, the four sides side by side, with 3 folds and the seam at corner 0: 4 parts, 2 seams.
| Blank, the rectangle the plate is cut from | 2004.0 mm × 1200.0 mm |
| Length of cut, every outline and hole | 6408.0 mm |
| Bends (3) down, the pattern drawn outside face up | 90.0° |
| Width | 601.00 mm |
| Depth | 401.00 mm |
| Length | 1200.00 mm |
| Girth | 2004.00 mm |
| Width of the blank | 2004.00 mm |
| Folds | 3 |
| Seams | 1 |
| P1 Side 1, -Y, long | 2004.00 mm |
| P1 Side 1, -Y, wide | 1200.00 mm |
| Plates | 1 |
| Triangular facets | 8 |
| Pattern extent X | 2004.00 mm |
| Pattern extent Y | 1200.00 mm |
| Developed area | 2,404,800 mm² |
| Total cut length | 6408.00 mm |
| Longitudinal seam length | 1200.00 mm |
How it is developed
True-shape development of flat sides. This is an exact development: the surface unfolds without stretching, so the pattern closes exactly.
- Every side is flat, so the blanks are exact: each is as long as the duct and as wide as the sides it takes, side by side.
- The blank is folded at three corners and closed by one seam at the fourth.
- The seams are drawn as plain edges. Add the lock seam, and a flange or a slip and drive at the ends, under Fabrication.
Checked before it can be exported
Every pattern SheetMorph draws is checked against the 3D part it comes from. For this example:
- Surface connectivity (passed): 8 facets form one closed band, open at both ends: every edge inside a part joins exactly two facets, every open edge one (V - E + F = 0).
- Developed edges equal true 3D lengths (passed): 24 facet edges compared between the 3D surface and the flat pattern (max deviation 4.55e-13).
- Shared edges and seam closure (passed): 7 internal edges are shared vertex-for-vertex between adjacent facets; 1 seam(s) have mating edges of equal true length (max deviation 2.27e-13).
- Developed facets consistently oriented (passed): All developed facets are counter-clockwise (outside face up); none is mirrored or degenerate.
- Developed area equals surface area (passed): Facet area in 3D and in the flat pattern agree (difference 4.66e-10).
- Cut outlines closed and non-overlapping (passed): 1 closed outline(s); no outline crosses itself or another outline.
Assumptions
- The pattern is developed on the mid-thickness surface; inside or outside sizes are converted to it by the thickness.
- Curves are chains of chords between division points.
- No seam, lap, weld-preparation or pressing allowance is added.
Limits of this module
- The duct is straight and square in section; a radius on the corners, cross-breaking and beading are not drawn.
- No lock seam, lap, end flange or slip and drive allowance is added here: add the seam and the end connections under Fabrication.
- Folds are sharp lines on the mid-thickness surface. Use the bend deduction under Fabrication for the inside radius and K-factor of the press brake.
- Curves are chains of straight chords between division points.
- No seam, lap, weld-preparation or pressing allowance is added, and plates are not nested onto stock sheets.
Conventions
Coordinate system. The part stands on the Z axis with End A at Z = 0. Angles round the axis are measured from +X toward +Y, counter-clockwise seen from +Z.
Divisions and thickness. A circle is divided into 4N equal chords. Sizes are inside, mid-thickness or outside sizes; the pattern is developed on the mid-thickness surface and the views show the sizes as entered.
Duct. The duct runs along the Z axis from End A at Z = 0 to End B, centred on the axis, its width along X and its depth along Y. Corners are numbered 0 (-X, -Y), 1 (+X, -Y), 2 (+X, +Y), 3 (-X, +Y) seen from End B; side 1 faces -Y, side 2 +X, side 3 +Y and side 4 -X.
Plates and seams. Under Pattern the sides are shared out among the plates: one piece wrapped round, with its seam at corner 0; two L-shaped pieces, sides 1 and 2 and sides 3 and 4, seamed at corners 0 and 2; a U of sides 1 to 3 closed by side 4, seamed at corners 0 and 3; or four flat sides, seamed at every corner. A corner inside a plate is a fold. Plates are drawn outside face up, standing on their End A edge.
Sizes and thickness. Width and depth are across the duct, as inside, mid-thickness or outside sizes; the length is along it. The blank is developed on the mid-thickness surface, one thickness more or less across the duct.
Change the sizes to your own in SheetMorph, check the drawing, add seam and flange allowances, and export DXF, PDF, SVG, CSV or G-code. Check every pattern against your own standards before cutting.
Open the rectangular ductOther folded work
- Box or Tray: A box, tray or pan folded from one blank: a base with four sides turned up, with or without a flange round the top.
- Gutter Mitre: A box or half-round gutter cut on a mitre for an outside or an inside corner: the blank with its folds and the mitred end.