This flat diameter of auger screw calculator develops the flat pattern of a screw-conveyor flight — the annular steel blank you cut before forming it into a helix. Enter the outside diameter, inside (shaft) diameter, and pitch above to get the flat blank dimensions.
How is the flat pattern calculated?
D = (A − B) ÷ 2 overall radial width E = √((π × A)² + C²) developed outside periphery F = √((π × B)² + C²) developed inside periphery G = (F × D) ÷ (E − F) inner radius of the flat blank Flat outside diameter = 2 × (G + D) Flat inside diameter = 2 × G
- A — outside flight diameter, B — inside (shaft) diameter, C — pitch
Example calculation
For A = 12″, B = 3.5″, C = 12″:
- D = (12 − 3.5) ÷ 2 = 4.25″
- E = √((π×12)² + 12²) = 39.56″
- F = √((π×3.5)² + 12²) = 16.28″
- G = (16.28 × 4.25) ÷ (39.56 − 16.28) = 2.97″
- Flat blank: inside ø 5.94″, outside ø 14.44″
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Frequently Asked Questions
What is the flat diameter of an auger screw?
It is the diameter of the flat annular steel blank that, when cut and stretched, forms one turn of the helical screw flight.
How do you develop a screw flight flat pattern?
Compute the developed outside and inside peripheries from the diameters and pitch, then use their difference and the radial width to find the blank’s inner and outer radii.
Why is the flight bigger when flat?
A flat blank is stretched and coiled into a helix, so its developed (flat) dimensions are larger than the finished screw’s diameters.