Calculator
Example Data Table
| Outer Diameter | Core Diameter | Pitch | Turns | Pieces | Thickness | Expected Use |
|---|---|---|---|---|---|---|
| 300 mm | 100 mm | 250 mm | 1 | 1 | 6 mm | Single short conveyor flight |
| 450 mm | 160 mm | 400 mm | 2 | 2 | 8 mm | Segmented heavy flight |
| 18 in | 6 in | 16 in | 1 | 1 | 0.25 in | Shop layout check |
Formula Used
Outer developed length per turn = √((π × outer diameter)² + pitch²)
Inner developed length per turn = √((π × core diameter)² + pitch²)
Blank width = ((outer diameter - core diameter) ÷ 2) + 2 × trim allowance
Sector angle in radians = (outer arc per piece - inner arc per piece) ÷ blank width
Flat outer radius = outer arc per piece ÷ sector angle
Flat inner radius = inner arc per piece ÷ sector angle
Area per piece = 0.5 × sector angle × (outer flat radius² - inner flat radius²)
Mean helix angle = tan⁻¹(pitch ÷ (π × mean diameter))
How to Use This Calculator
- Enter the outside diameter of the finished screw flight.
- Enter the core or shaft diameter at the flight root.
- Add the pitch for one full revolution.
- Enter the number of turns needed.
- Choose how many flat pattern pieces will be cut.
- Add thickness, trim allowance, overlap, kerf, and scrap values.
- Press Calculate to view the result above the form.
- Use CSV or PDF buttons to save the calculation.
Understanding Screw Flight Layout
A screw flight flat pattern changes helical geometry into a cut blank. The calculator helps you estimate that blank before rolling, pressing, or forming begins. A flight has an outside diameter, an inside diameter, and a pitch. Pitch is the axial travel made by one full revolution. These values define the outer and inner helical edge lengths.
Why Flat Pattern Numbers Matter
A wrong blank can waste plate and shop time. The outer edge travels farther than the inner edge. That difference creates an annular sector, not a simple washer. The calculator uses the developed outer helix and inner helix. It then finds the sector angle and blank radii that match those lengths. This gives a practical starting point for marking, cutting, and forming.
Material and Allowance Planning
Real fabrication needs allowance. Plate thickness, trimming stock, kerf, and weld overlap can affect the final blank. This tool includes those values so the estimate is closer to shop use. The result also shows blank area and approximate mass. That helps with ordering plate, checking handling weight, and comparing layouts.
Physics Behind the Pattern
The calculation is based on helix geometry. Each edge of the flight follows a spiral path around the shaft. One revolution becomes a right triangle when developed. The circumference is one leg. Pitch is the other leg. The helical length is the hypotenuse. Outer and inner helical lengths are then related to two arcs in the flat blank.
Best Use in the Workshop
Use accurate measurements. Keep all units consistent. Measure the core diameter at the flight root, not at a worn edge. Use a realistic density for your material. Add trimming allowance when the final formed flight must be machined or fitted tightly. Use the pattern as an estimating and layout guide. Always verify the blank with a small template when tolerances are strict.
Final Checks
Compare the sector angle with your cutting process. Very small angles can be hard to handle. Very large turns may need segmented flights. Review the developed lengths, blank radii, and material area together. These checks help reduce error before the plate is marked. Record each revision so repeat parts stay consistent across later production batches and crews.
FAQs
What is a screw flight flat pattern?
It is the flat annular sector used to form a helical screw flight. The pattern gives the blank radii and sector angle before forming.
Why is pitch important?
Pitch controls the axial travel per revolution. It changes the developed helix length and affects the final blank geometry.
What is the core diameter?
Core diameter is the shaft or tube diameter where the inner edge of the flight sits. Measure it at the flight root.
Why does the calculator use two developed lengths?
The outer edge travels a longer helical path than the inner edge. Both paths are needed to create a correct annular sector.
Can I calculate segmented flights?
Yes. Enter the number of pattern pieces. The calculator divides the developed lengths across those pieces.
What does trim allowance do?
Trim allowance adds extra radial material. It helps when the formed flight needs machining, fitting, or final edge cleanup.
Is the result ready for final cutting?
Use it as a strong layout estimate. For tight work, verify the result with a template or forming trial.
Why is density included?
Density allows an estimated mass calculation. It helps with plate handling, material planning, and job costing.