Shelle Parsons Compression Spring Fundamentals Compression springs are everywhere — from ballpoint pens to automotive suspensions. Designing one means balancing wire diameter, coil diameter, free length, and active coils to achieve your target spring rate and deflection without exceeding stress limits. Key Formulas Spring Rate (Stiffness) k = Gd⁴ / (8D³Nₐ) k = spring rate (lbs/in or … Read more
American Wire Gauge (AWG) Reference AWG is the standard wire sizing system in North America. The gauge number is inversely proportional to wire diameter — smaller numbers = thicker wire. This chart covers the most commonly used sizes for power wiring, electronics, and industrial applications. AWG Wire Specifications — Solid Copper AWG Diameter (in) Diameter … Read more
Choosing a Bearing Wrong bearing choice is one of the most expensive design mistakes — it causes premature failure, excessive noise, heat, and downtime. This guide covers the major bearing types, when to use each, and the key selection criteria. Bearing Type Comparison Type Radial Load Axial Load Speed Precision Cost Maintenance Deep Groove Ball … Read more
Minimum Thread Engagement How deep does a bolt need to thread into a part before the threads strip? This is one of the most common questions in fastener design — and the answer depends on the relative strength of the bolt and the tapped material. Rule of Thumb Tapped Material Minimum Engagement Recommended Engagement Steel … Read more
Choosing the Right O-Ring Material The o-ring cross-section and groove are important, but the material determines whether your seal actually works in your application. Temperature, chemical exposure, pressure, and dynamic vs. static service all influence material choice. Material Comparison Table Property Nitrile (NBR) Viton (FKM) EPDM Silicone PTFE (Teflon) Neoprene (CR) Temp Range (°F) -40 … Read more
Choosing the Right Engineering Plastic Engineering plastics bridge the gap between commodity plastics (like polyethylene) and metals. They offer strength, wear resistance, chemical resistance, and dimensional stability that commodity plastics can’t match — at a fraction of the weight and cost of metals. Properties Comparison Table Property Nylon 6/6 Delrin (POM) PEEK Polycarbonate UHMW-PE Acetal … Read more
Calculating Shaft Diameter Shafts transmit torque and support loads. Designing a shaft means finding the minimum diameter that can handle the combined bending and torsional stresses with an adequate safety factor. Here’s the practical approach. Pure Torsion (Torque Only) For a solid circular shaft transmitting torque T: Shear stress: τ = 16T / (πd³) Minimum … Read more
Quick Reference: Beam Deflection & Stress These are the formulas you’ll use most often in mechanical and structural design. Memorize the first two (center-loaded simply supported and end-loaded cantilever) — every other case is a variation. Simply Supported Beam Case 1: Center Point Load Parameter Formula Max Deflection (at center) δ = PL³ / 48EI … Read more
Understanding Bolt Preload Bolt preload is the tension (clamping force) induced in a bolt when it’s tightened. This preload is what holds your joint together — not the bolt’s ultimate tensile strength. A properly preloaded joint resists external loads by maintaining clamping force on the parts, preventing slippage and fatigue. Why Preload Matters More Than … Read more
What is Coefficient of Thermal Expansion (CTE)? The Coefficient of Thermal Expansion (CTE) tells you how much a material will expand or contract when its temperature changes. This is critical for assemblies where dissimilar materials are joined, or for parts that experience wide temperature swings. Formula: ΔL = α × L₀ × ΔT ΔL = … Read more