Mechanical Engineering Calculators
Free spring calculators for compression, extension, and torsion springs. Wahl stress, Goodman fatigue, spring rate - per SMI and IS 7906 standards.
Mechanical Engineering Calculators - Precision Spring Design
Springs are among the most widely used mechanical components in engineering - from automotive suspensions to precision medical devices. Correct spring design requires computing spring rate, stress under load, safety factors, and fatigue life. These calculators implement the industry-standard Wahl correction factor and Goodman fatigue criterion per the SMI Design Handbook and IS 7906.
Three Spring Design Calculators
Compression Spring Calculator - Spring rate (k = Gd⁴/8D³Na), Wahl stress correction factor (Kw = (4C−1)/(4C−4) + 0.615/C), corrected shear stress (τ = Kw × 8PD/πd³), solid height, free length, and buckling check. Supports 10 standard spring materials (music wire, hard-drawn wire, chrome-silicon, stainless steel 302/304/316, phosphor bronze) with material-specific G modulus and allowable stress values. Per IS 7906.
Extension Spring Calculator - Spring rate, initial tension force (Fi), hook bending stress (Kb correction), hook torsional stress (Kt correction), Wahl body stress, and Goodman fatigue safety factor for cyclic loading. Supports 5 hook types (machine, crossover, extended, side, half-twist). Per IS 7906-4.
Torsion Spring Calculator - Angular spring rate (k = Ed⁴/10.8DN, in N·mm/degree), KB bending stress correction factor, bending stress under moment, coil diameter change under load, mandrel clearance verification (inner diameter must exceed mandrel under full load), leg compliance, and Goodman fatigue criterion. Per IS 7906-3.
Spring Design Fundamentals
Spring Index (C = D/d) - The ratio of mean coil diameter to wire diameter. Practical range: C = 4–12. C < 4 is very difficult to manufacture; C > 12 has reduced efficiency and increased buckling risk. All three spring calculators compute C and flag values outside the practical range.
Wahl Correction Factor - For C = 6, Kw ≈ 1.25 - actual stress is 25% higher than the uncorrected simple torsion formula predicts. Always design with Kw included.
Goodman Fatigue Criterion - For springs under cyclic loading (which is nearly every spring in service), static analysis alone is insufficient. A Goodman safety factor above 1.3 is typically required for high-cycle applications. All three spring calculators compute this automatically.
Frequently Asked Questions
What is the difference between compression, extension, and torsion springs?
Compression springs resist compressive forces (push back when squeezed). Extension springs resist tensile forces (pull back when stretched). Torsion springs resist torque (wind or unwind when a moment is applied to their legs). Each has different design equations - use the Compression, Extension, or Torsion calculator as appropriate.
What shear modulus value should I use for music wire?
Music wire (ASTM A228): G = 81,500 MPa. Stainless steel 302/304: G = 69,000 MPa. Phosphor bronze: G = 41,400 MPa. The Compression Spring Calculator includes these values in the material dropdown.
How do I check if a compression spring will buckle?
The buckling risk is assessed by slenderness ratio (free length ÷ mean coil diameter). Risk is significant when L/D exceeds ~5.2 for fixed-end conditions. The Compression Spring Calculator computes this and flags the warning.
What is mandrel clearance in torsion spring design?
When a torsion spring is loaded, its coil inner diameter decreases. If fitted over a mandrel, the reduced inner diameter must not contact it. The Torsion Spring Calculator computes the inner diameter under full load and compares it to the specified mandrel diameter.