Inlet Box Scroll: flat pattern
The scroll of a fan inlet box laid flat: its straight sides and arc unrolled, each line across as deep as the box is there. The scroll of a fan inlet box laid flat: the plate round the bottom of the box, its straight sides and arc unrolled, as deep at every line across it as the box is there, for a box deeper at the top than at the bottom.
Open the inlet box scroll in SheetMorphConfigurations
- Symmetric. The two sides of the box alike, either side of the centre of the arc (shop Type 1).
- Off-centre. The arc nearer one side: the two half-widths of the top are entered on their own (shop Type 2).
- With an inlet step. The scroll set back from the back plate at the top, stepping back to it part way down, and the front upright for a short way below the top (shop Type 3).
A worked example
The symmetric configuration with the sizes SheetMorph opens with, in mm. One plate, the scroll, with its lines across marked with their lengths: 1 part, 0 seams.
| Blank, the rectangle the plate is cut from | 6574.2 mm × 750.0 mm |
| Length of cut, every outline and hole | 14695.6 mm |
| Radius of the arc | 1000.50 mm |
| Left side, corner to the arc | 1989.10 mm |
| Arc | 2595.98 mm |
| Right side, arc to the corner | 1989.10 mm |
| Length of the scroll | 6574.18 mm |
| Angle of the arc | 148.66 ° |
| Left side meets the arc, above the centre | -270.19 mm |
| Right side meets the arc, above the centre | -270.19 mm |
| Width at the ends | 750.00 mm |
| Width at the bottom of the arc | 374.93 mm |
| Divisions of the arc | 10 |
| One division, left of the bottom | 259.60 mm |
| One division, right of the bottom | 259.60 mm |
| Angle of one division, left | 14.87 ° |
| P1 Scroll, long | 6574.18 mm |
| P1 Scroll, wide | 750.00 mm |
| Plates | 1 |
| Triangular facets | 24 |
| Pattern extent X | 6574.18 mm |
| Pattern extent Y | 750.00 mm |
| Developed area | 3,513,606 mm² |
| Total cut length | 14695.56 mm |
| Longitudinal seam length | 0.00 mm |
How it is developed
Parallel-line development: the U unrolled, every line across it as long as the box is deep there. This is a triangulated approximation: the curved surface is divided into small flat triangles, each laid out at its true size. The finer the division, the closer the pattern is to the surface; SheetMorph states the deviation it found.
- Every line across the scroll is square to the front view, so the scroll lays flat exactly: its back edge is a straight line as long as the U is round, and each line across it is as long as the box is deep there.
- The straight sides lay flat as straight edges. The arc, of 148.6644 degrees, is divided into 10, 5 each side of the bottom, and laid flat at its true length: each division is R x its angle along the back plate, and the depth across is marked at each.
- The scroll is welded to the front and the back plates along its two long edges.
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): 24 facets form one open sheet, the scroll: every edge inside a part joins exactly two facets, every open edge one (V - E + F = 1).
- Developed edges equal true 3D lengths (passed): 72 facet edges compared between the 3D surface and the flat pattern (max deviation 4.55e-13).
- Shared edges and seam closure (passed): 23 internal edges are shared vertex-for-vertex between adjacent facets; 0 seam(s) have mating edges of equal true length (max deviation 0).
- 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 front and the back plates of the box, and its inlet flange, are not drawn; the scroll is the part that is rolled.
- The front of the scroll is one inclined plane (with an inlet step, upright and then inclined); a box that changes depth along a curve is not modelled.
- The step is square to the back plate: it is a notch in the edge of the scroll.
- 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.
Front view. The box stands upright and is drawn from the front in the XZ plane, the centre of the bottom arc at the origin and Z up. The top of the box is C above the centre; its corners are A1 to the left and A2 to the right of the centreline (A / 2 each for a symmetric box). The sides run down from the corners as straight lines that touch the arc of radius R.
Side view. The depth runs from the back plate, at Y = 0, toward the front, at -Y. The front of the scroll slopes from B1 at the top to B2 at the bottom of the arc. With an inlet step the front stands upright, B1 + D1 from the back plate, for E below the top, then slopes to B2; the back edge of the scroll is D1 from the back plate at the top, D2 at the height C2 above the centre, and on the back plate below it.
Scroll. The arc is divided into the number of divisions entered, 10 as the shop divides it: half of them each side, in equal angles from where the side meets the arc to its bottom. One division each side is dimensioned along the back plate. The scroll is one plate, laid flat with its back edge along the top of the drawing, straight where it lies on the back plate, and its two ends, at the top of the box, at the sides. Every line across it is drawn, and dimensioned as the shop draws it: the length overall and in its parts along the back plate, the depth at each end, and the depth across at the tangent points and every division. Its two ends, at the top corners of the box, are End A on the left and End B on the right.
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 inlet box scrollOther hoods, plenums and cyclones
- Canopy: An extraction hood: a skirt round a rectangular opening, four sloping sides and a collar for the duct, in the middle or against a wall.
- Canopy, Round Collar: An extraction hood for a round duct: a skirt round a rectangular opening, a rectangle-to-round sloping part and a round collar, in the middle or against a wall.
- Plenum Box: An open box folded from one blank with a row of round spigots on its back or a side: the box with every hole marked, and the spigots unrolled.
- Cyclone: A cyclone dust collector from its barrel diameter, to Stairmand or Lapple proportions or your own: barrel, cone, roof, inlet duct and gas outlet tube.