Volume Damper: flat pattern

A round sleeve with one blade, or a rectangular sleeve with a row of blades: the blades cut with their clearance and the sleeve with its shaft holes. A damper to set the flow in a duct: a round sleeve with one round blade, or a rectangular sleeve with a row of blades, the blades cut with their clearance and the sleeve with the holes for the shafts.

Configurations

• Round. A round sleeve with one round blade on a shaft across its middle.
• Rectangular. A rectangular sleeve with one or more blades, one above another, each on its own shaft.

A worked example

The round configuration with the sizes SheetMorph opens with, in mm. 2 plates: the sleeve with its two shaft holes, and the blade: 2 parts, 2 seams.

How it is developed

Parallel-line development of the sleeve; true shape of the blade. 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.

• The sleeve unrolls to a rectangle as long as the sleeve and as wide as its girth, with a shaft hole on each side at half its length.
• Each blade is the inside of the sleeve less 3 all round, so that it turns freely; the shaft runs across its middle.
• The quadrant is fixed on the outside of the sleeve over the shaft hole on +X.

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): 126 facets form a sleeve and the blade in it: every edge inside a part joins exactly two facets, every open edge one (V - E + F = 1).
• Developed edges equal true 3D lengths (passed): 378 facet edges compared between the 3D surface and the flat pattern (max deviation 9.31e-13).
• Shared edges and seam closure (passed): 124 internal edges are shared vertex-for-vertex between adjacent facets; 1 seam(s) have mating edges of equal true length (max deviation 2.84e-14).
• 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 4.07e-10).
• Cut outlines closed and non-overlapping (passed): 2 closed outline(s); no outline crosses itself or another outline.
• HOLE-SHAFT-X+ lies within its plate (passed): 24 points of the hole compared with the edges of the plate; its developed area is 111.4569.
• HOLE-SHAFT-X- lies within its plate (passed): 24 points of the hole compared with the edges of the plate; its developed area is 111.4569.

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 blades are flat plates: no stiffening crimps, folded edges or seals are drawn.
• The shafts, bearings, quadrant and bolts are not drawn; only the holes for the shafts are marked.
• Blades of a rectangular damper are all alike; opposed and parallel blades differ only in how they are linked, which is not drawn.
• 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.

Sleeve. The sleeve runs along the Z axis from End A at Z = 0 to End B. A round sleeve is cut along its bottom (-Y); a rectangular one has its width along X and its height along Y and is folded in one piece, seamed at corner 0. The shafts run along X through the middle of the sleeve, at half its length.

Blades. The blades are drawn shut, square to the sleeve. A blade is as large as the inside of the sleeve less the clearance all round; in a rectangular damper the blades share the inside height equally, each turning on a shaft along its middle. The quadrant that sets the blades is fixed over a shaft hole on +X.

Sizes and thickness. The diameter, or the width and height, of the sleeve are entered as inside, mid-thickness or outside sizes; the inside of the sleeve is one thickness less than its mid-thickness size. The shaft holes are drawn the diameter of the shaft.

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.

Other dampers, doors and attenuators

• Access Door: A door over an opening in the side of a duct: the side with its opening, and the door folded as a pan, single skin or with an inner skin.
• Sound Attenuator: The casing of a sound attenuator: rectangular with a row of splitters, or round with a pod on its axis.