The coordinate measuring machine, or CMM, determines the X, Y and Z coordinates of points on the surface of a part. A contact probe (touch-trigger or scanning), sometimes an optical or laser sensor, moves on three axes and records these points. Software deduces geometric elements from them (planes, circles, cylinders, cones), then calculates dimensions, distances, angles, form and position, which it compares with the tolerances on the drawing.
There are several types: gantry or moving-bridge machines, installed in a metrology room and very accurate; portable articulated arms, more flexible to use near the workshop; optical-sensor machines for small or fragile parts. Their performance is verified under the ISO 10360 series. For the finest measurements, the room is controlled at 20 °C, the reference temperature of metrology.
The CMM is the natural tool for the geometric tolerances of GPS dimensioning: position, coaxiality, perpendicularity relative to datums. It is used for the first article, for monitoring complex parts, castings, 5-axis machined parts or tooling. It has its limits: probe accessibility, flexible parts, measurement and programming time. The program is written from the drawing or the CAD model, which has a cost that is spread over a batch. It does not replace a roughness tester for surface finish.
In a quote request
Specify whether a CMM report is required, on which dimensions (preferably marked on a “ballooned” drawing, that is, one on which each dimension carries a number), on which parts (the first, a sample, all) and in what format (PDF, spreadsheet). Attach the 3D model in STEP format to ease programming. Measuring time is charged: limit inspection to the useful characteristics. See the guide dimensional inspection and first article.