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Engineering reference

The thinking behind the drawings.

Measurement science and material mechanics decide whether a drawing is achievable. These are the parts we work from — written down, with the numbers, so you can check them.

Drawings and inspection
GD&T, and why two ±0.1 mm holes aren’t equally roundCoordinate tolerancing vs true position, datum reference frames, and the bonus tolerance nobody explains.Engineering drawings — what makes a drawing a specificationTitle blocks, general tolerance notes, chain vs baseline dimensioning, and first-angle vs third-angle projection.
Metrology
Why a part passes on one gauge and fails on anotherMeasurement uncertainty, the 20 °C assumption, and the 10:1 rule. Why a tolerance you cannot measure is not a tolerance.
Material mechanics
Springback, and why your bend angles moveElastic recovery, what drives it, indicative values by material — and why K-factor and springback are different problems.Poisson’s ratio, and why metal thins when you pull itWhy a bend thins on the outside and thickens on the inside — and why that is what your K-factor is locating.Young’s modulus — stiffness is not strengthWhy a stronger steel will not stop a bracket bending, and why aluminium deflects three times as far.Strength, ductility and toughnessThree different things people call “strong” — and why the toughest material is almost never the strongest one.
Materials and processes
Material grades, and why “stainless” isn’t one materialS235JR, 304, 316, 6061 and 5052 compared on what actually differs — not just the name on the spec sheet.Thermal expansion, and why your gauge disagrees with itselfWhy a part is a different size at a different temperature, and how much it moves depends entirely on what it’s made of.Fatigue, and why a “safe” stress can still break a partStatic strength checks compare stress to yield. They say nothing about a load repeated thousands of times a day.Heat treatment, and why “harden it” isn’t a specAnnealing, hardening and tempering do different — sometimes opposite — things to the same material.Galvanic corrosion, and the ranking most designers have never seenTwo metals, an electrolyte, and a small battery you didn’t mean to build — why the anode corrodes and the cathode doesn’t.
Working tools: free engineering calculators