Coordinate Measuring Machines, CMM
A coordinate-measuring machine (CMM) is a device for dimensional measuring. It is an NC machine that used to move a measuring probe to obtain the coordinates of points on an object surface. CMM machines are used to measure the dimensions of target objects. Often these parts have tolerances as small as .0001". The CMM machine uses an X-Y-Z grid to determine its position on a worktable. The probe is used to touch different spots on the part being measured. The coordinate-measuring machine then uses the X, Y, Z coordinates of each of these points to determine size and position. There are newer coordinate-measuring machine models that have probes that drag along the surface of the part taking points at specified intervals. This method of CMM inspection is more accurate than the conventional touch-probe method and most times faster as well. The next generation of scanning, known as laser scanning, is advancing very quickly. This method uses laser beams that are projected against the surface of the part. Many thousands of points can then be taken and used to not only check size and position, but to create a 3D image of the part as well. This "point-cloud data" can then be transferred to CAD software to create a working 3D model of the part. The laser scanner is often used to facilitate the "reverse engineering" process. This is the process of taking an existing part, measuring it to determine its size, and creating engineering drawings from these measurements. This is most often necessary in cases where engineering drawings may no longer exist or are unavailable for the particular part that needs replacement.
