Screw conveyor flight calculator
Enter the flight outside diameter, shaft diameter, pitch and number of turns. You get the flat ring for one turn, its sector angle and the true inner and outer arc lengths. The pattern needs a forming allowance.
Enter your measurements
Outer arc
989.1mm
Approximate, within ±33.7 mm
- Inner arc
- In the app
- Cut length
- 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.
How to lay it out
Swing the two circles
From one centre, draw the inner circle at radius r and the outer circle at the calculated radius R.
Mark the ring angle
Draw one radius line, then mark the ring angle φ from it; the rest of the circle, 360° − φ, is cut away.
Cut the ring
Cut along both circles and both radius lines. Cut one ring for each turn.
Form the flight
Open the ring into one turn of pitch S in a press or by stretching, so the inner edge sits on the shaft.
Join and weld
Weld the rings end to end with radial welds and weld the inner edge to the shaft.
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.
Method and formula
A screw flight is a helicoid. It is curved in two directions, so no flat ring folds into it without stretching: the pattern is approximate and needs forming. The standard ring keeps the two edge lengths exact instead.
- Helix length per turn at radius ρ: ℓ(ρ) = √((2πρ)² + S²). L_D = ℓ(D ÷ 2) on the outer edge, L_d = ℓ(d ÷ 2) on the inner edge.
- Flight width b = (D − d) ÷ 2.
- Inner radius r = b × L_d ÷ (L_D − L_d); outer radius R = r + b.
- Ring angle φ = (L_D − L_d) ÷ b radians, always less than a full circle.
The inner arc equals L_d, the outer arc equals L_D and the radial width equals b, all exactly. Between the edges the flat ring is slightly longer than the helix, so forming compresses the middle of the flight. Trueflat reports the largest strain, φ√(S² + 4π²c²) ÷ (2πS) − 1 with c = r − d ÷ 2, and the largest length difference in one turn, φc − S√(4π² − φ²) ÷ (2π). Above 15 % strain the ring would tear or buckle in a cold press, so the input is rejected.
Thickness runs along the shaft, so the diameters are the edges of the sheet and there is no inside or outside measurement.
Worked example
D = 300 mm, d = 60 mm, S = 300 mm: L_D = 989.07 mm, L_d = 354.30 mm and b = 120 mm. The ring angle is 303.08°, so 56.92° is cut away. The inner radius is 66.98 mm and the outer radius 186.98 mm. The largest strain is 6.49 % and the largest length difference 33.72 mm per turn.
Questions
Is the flight pattern exact?
No. A helicoid cannot be unrolled flat, so the ring needs a forming allowance. The inner and outer edge lengths and the width are exact. Between the edges the ring is longer than the flight by up to 33.72 mm per turn in the example, with a largest strain of 6.49 %. Above 15 % the input is rejected.
Why is part of the circle cut away?
The flat ring has larger radii than the flight itself, so a full circle would be too long. The ring angle φ makes the inner and outer arcs exactly one helix turn each; the remaining 360° − φ is scrap.
What pitch should I use?
Conveyor flights are usually pitched between half and one and a half times the outside diameter. The calculator accepts D ÷ 10 to 3D, as long as the forming strain stays at or below 15 %.
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