Before choosing a CMM machine, you need to know about the different types of measuring machine. All CMMs have three orthogonal axes, X, Y and Z, but in varying structures. 

1. Bridge CMM Machine

The bridge-type coordinate measuring machine is the most popular style. The typical 3D bridge CMM machine allows the probe to move along X, Y and Z, which are orthogonal to each other, each axis has a sensor for monitoring the probe position, usually with micrometer precision. When the probe contacts the object, the machine samples the three sensors, then measuring the location of one point on the surface. And repeat the process until generating an area that describes the surface. Bridge machines offer better accuracy than other types of coordinate measuring machines and have a low cost and ability to maintain accuracy and repeatability.

2. Cantilever CMM Machine

Cantilever machines are usually used for the measurement of relatively small parts, and gauges, master parts as its high accuracy and low measurement uncertainty, providing open access to the operator on three sides. The X-axis measuring beam is attached on the side of a rigid structure housing the Y-axis, which limits the size of the X beam. Large support base combines with low weight enables Cantilever coordinate measuring machine moves fast. The cantilever type machine also has good capability of automatic loading and unloading. 

3. Gantry CMM machine

Gantry type coordinate measuring machines have similar structures to bridge machine, but it’s primarily used to measure large and heavy parts. Most gantry machines are directly mounted on the floor, which is safe setup allows the programmer to easily walk up to the part and make the operation more conveniently. The operator can access the machine in unrestricted, make small features that can be measured carefully. In addition, the surface plates for smaller components are easily inserted into the gantry machine, decrease the difficulty of measurement and complexity. 

4. Horizontal Arm CMM Machine

Horizontal Arm type machine has a different configuration where a vertical column (X-axis) and a horizontal arm (Z) mounted on a saddle that runs vertically up and down the X-axis. The Y-axis is the length of a surface plate or a long beam. There are two basic types: plate mounted and two runway mounted. Horizontal arm CMM offers a lower accuracy than the three above CMMs, but it is useful for measuring large surfaces or difficult to reach features including large thin-walled/sheet-metal type components mounted in fixtures that represent car body position, like car door.