Coordinate Measuring Machine

Coordinate-Measuring Machines, (CMM), are mechanical systems designed to move a measuring probe to determine the coordinates of points on the surface of a workpiece. Coordinate-measuring machines consist of four main components: the machine itself, the measuring probe, the control or computing system, and the measuring software. They are often used for dimensional measurement, profile measurement, angularity or orientation measurement, depth mapping, digitizing or imaging, and shaft measurement. CMMs are offered with features like crash protection, offline programming, reverse engineering, shop floor suitability, SPC software and temperature compensation. The machines are available in a wide range of sizes and designs with a variety of different probe technologies. They can be controlled and operated manually, or by CNC or PC controls.
CMMs are offered in various configurations such as benchtop, free-standing, handheld and portable. Ideally, a CMM would be coupled with GD&T practices and programs automated to continoulsy check and send feedback to various manufacturing processes in the event of an error in the manufactured part geometry.
Pictured is an example of a CMM measuring head. It is reffered to as an Ultra Precise Test Sphere, and it is just that. It is spherical within 2.5 micro inches (63.5 n m) maximum and has a surface finish that is better than 0.5 micro inches (12.7 n m) Ra. This is ten times more accurate than high quality bearing balls. Spheres of this quality are simply not commercially available.