Inspection, Metrology & GD&T Calculators

Making the part is half the job. Proving it is right is the other half. This hub collects the inspection, tolerance and measurement tools on Machinist Central for machinists, inspectors and quality engineers.

Start with tolerances. The ISO fit calculator gives the limits for hole and shaft fits such as H7/g6, and the ISO machining limits tool looks up deviations by size and IT grade. The stack-up tool adds tolerances along a chain using both worst case and RSS methods. The thermal expansion calculator shows how much a part grows when it is warm, which matters on tight bores.

For GD&T, the true position calculator turns measured X and Y deviations into a position value and checks it against the tolerance, including bonus tolerance at MMC.

Many checks still happen on the surface plate. Build gauge block stacks, set a sine bar or compound sine plate to an angle, check a diameter in a V-block, measure a dovetail over pins, and work out tapers and radius and chord sizes.

The surface finish tool converts between Ra, Rz and RMS, and the hardness converter cross-references the Rockwell, Brinell and Vickers scales. For the gauges themselves, the Gage R&R analyzer shows how much of your tolerance is used up by measurement variation.

The guides explain GD&T symbols, gauge block care and sine bar setups. The tools help with the math, but the drawing and the standard it calls for always decide whether a part passes.