FabLayout

Spiral chute calculator

Enter the chute outside diameter, column diameter, pitch, total sweep, segments and wall heights. You get the base ring segment and the outer and inner wall strips. The base needs forming.

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Enter your measurements

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1:1 PDF and DXF files of this flat pattern are made in Trueflat, ready for print, plasma, laser or waterjet. It works offline on site.

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2,619.1 mm650.5 mm
Flat pattern: cut on the bold outline, bend on the dashed blue lines, the thin lines are marking lines

Seam

3,849.0mm

Approximate, within ±18.1 mm

Outer arc
In the app
Inner arc
In the app
Sheet size
In the app

Every result is in Trueflat

The free web version shows the main result and the drawing. Trueflat gives you every mark and measurement, and exports a cut sheet. It is free to download.

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How to lay it out

  1. Lay out the base segment

    From one centre, draw the inner and outer base arcs at the calculated radii and mark the segment angle between two radius lines.

  2. Lay out the outer wall

    Draw a parallelogram with vertical ends as high as the outer wall. Its bottom edge runs (D ÷ 2) × segment sweep along and climbs by the segment's rise.

  3. Lay out the inner wall

    If there is an inner wall, draw the same kind of parallelogram for the column diameter d and the inner wall height.

  4. Form the base

    Press or pull each base segment into its helical shape and fit it round the column.

  5. Roll and weld the walls

    Roll the wall strips to their diameters, weld them along the base edges and join the segments end to end.

Good to know

  • This pattern is approximate; the result card shows how close it is.
  • Source: The standard flight-ring development used in conveyor work, derived here from first principles: the inner and outer edges keep the true helix lengths and the radial width is exact; the strain and length difference are proved in closed form. Checked against an independent reference implementation in Trueflat. Walls are cylinders developed exactly.

Method and formula

A spiral chute is a helical floor that winds round a column, with an outer wall and, if you want, an inner wall. The total sweep is split into identical segments of at most one full turn each.

Base. Each segment is a slice of the same flat ring as a conveyor flight, for the chute outside diameter D, column diameter d and pitch S. The inner and outer arcs and the radial width are exact. The surface itself cannot be unrolled, so the base is approximate and needs a forming allowance. Trueflat reports the largest strain and the largest length difference across the segment, and rejects inputs above 15 % strain.

Walls. The walls are cylinders, so they are exact. Unrolled, a wall is a parallelogram:

  • run along the bottom = (D ÷ 2) × segment sweep in radians;
  • the bottom edge climbs S × segment sweep ÷ 360°;
  • height = outer wall height ho (or inner wall height hi on the column).

When the chute makes more than one turn, each wall must be at least 5 mm lower than the pitch so it does not hit the floor above. Thickness runs along the axis, so the diameters are the sheet edges and there is no inside or outside measurement.

Worked example

D = 600 mm, d = 200 mm, S = 400 mm, 360° in one segment, outer wall 120 mm, inner wall 80 mm. The base ring angle is 338.64° with inner radius 126.02 mm and a largest strain of 1.62 %. The outer wall is a parallelogram whose sloping bottom edge is 1926.93 mm long and climbs 400 mm, with an area of 226 194.67 mm²; the inner wall is 50 265.48 mm².

For 900° in 3 segments (D = 1200 mm, d = 300 mm, S = 800 mm, outer wall 150 mm), each segment sweeps 300° and climbs 666.67 mm, and the largest base length difference is 51.06 mm.

Questions

Which parts are exact?

The walls are exact: they are cylinders and unroll to parallelograms. The base is approximate. Its edges and width are exact, but the helical floor stretches between them, by up to the calculated length difference (51.06 mm per 300° segment in the second example). Allow for it when forming.

How is this different from a conveyor flight?

The flight is a full ring welded to a shaft, cut one per turn. A chute floor can be any sweep split into equal segments and adds walls to keep material on the floor. Its base uses the same ring formula.

How many segments should I use?

Each segment can be at most one full turn. More segments make smaller pieces that are easier to press and handle, at the cost of more joints.

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