In addition, the two types of machine can be characterized to some degree by the levels of accuracy they each achieve (although there is a considerable degree of overlap based on the design of an individual machine), by the size of part they can handle, and by application. | Fixed bridge L-shaped bridge Column Gantry In addition the two types of machine can be characterized to some degree by the levels of accuracy they each achieve although there is a considerable degree of overlap based on the design of an individual machine by the size of part they can handle and by application. The prospective buyer user of a CMM cannot make an intelligent choice of the type of machine that will best meet his needs let alone the specific make and model of CMM until he thoroughly evaluates and plans both the specific intended application of the CMM and the overall manufacturing and quality context in which it will operate. Table 1 provides a general comparison of CMM types applications and levels of measurement accuracy a CMM user can expect. Table 1 Typical CMM specifications Application CMM type Bearing type Minimum measurement mm in. Laboratory quality a Laboratory grade Vertical moving bridge Air bearings Clean room Vertical moving bridge Air bearings Production machines Open shop Vertical moving bridge Air bearings Sheet metal Horizontal with fixed x-y axis Recirculating bearing packs Clean room and shop Vertical moving bridge all horizontal Air roller bearings a These CMMs have specific environments into which they must be installed to maintain their rated accuracies. Experience clearly shows that the user who simply buys a CMM and places it in use without considering the impact of the unit on the manufacturing process will almost invariably fail. On the other hand the user who determines the results desired from the CMM the resources required to achieve those results and the effect of the CMM on the overall manufacturing process will likely realize the maximum benefits a CMM can provide. Evaluation and planning are further discussed in the section CMM Implementation in this article. Vertical CMMs Vertical CMMs which have the probe or sensor mounted on the .
