3D bridge CMM machines typically allow probe movement along three axes, X, Y, and Z, which are orthogonal to each other in a three-dimensional Cartesian coordinate system, as shown in the figure below.  Each axis is equipped with a sensor that continuously monitors the position of the probe along that axis, usually with micrometer precision.  Whenever the probe comes into contact with (or otherwise detects) a specific location on the object, the machine samples the three position sensors, which allows it to determine the location of a single point on the object's surface.  This process is repeated as many times as necessary, with the probe being moved with each repetition, until a point cloud is produced that describes the surface areas of interest.

Bridge machines have become extremely popular due to the simplicity of their design and the simplicity with which they can be constructed.  Bridge machines are inexpensive to construct and have the ability to maintain accuracy and repeatability over an extended period of time.  In most cases, a precision granite plate with two legs supporting the X-axis carriage serves as the foundation for the machine.  One side of the bridge is typically driven while the other side serves as a slave side and is allowed to float freely on the water beneath it.  In order to allow for friction-free movement and minimize mechanical interaction, 95% of all bridge machines are equipped with air bearings.

Aside from a few exceptions, machines are built in sizes that range from 300x300x300 mm (XYZ) to 2000x5000x1500mm (XYZ), with some exceptions.  Bridge machines are the workhorses of CMMs, performing a variety of tasks.  However, there are both advantages and disadvantages associated with their use in everyday life.  For example, because of the uprights that support the X-axis beam, it is sometimes difficult to gain access to the part being measured.  A crane or a lift truck is required to lift heavy components onto the plate, which may result in an accident with the machine if the components are not properly supported.  The accuracy of most bridge systems is typically better than that of other types of coordinate measuring machines, and when it comes to a system for machined parts with higher tolerances, a bridge system is difficult to beat.

A cantilever is a structure that is supported by another structure.  The cantilever CMM machine was the initial design of Ferranti in Scotland in the 1970s, and today they are produced in small quantities, usually as shop floor hard bearing machines for hard bearing applications.  When measuring relatively small parts, they are typically used because the operator has three sides of open access to the measurement area.  The X-axis measuring beam is attached to the side of a rigid structure that also houses the Y-axis measurement system. . As a result of the inherent rigidity of the X beam, the size of the X beam is limited, and the machine is only suitable for smaller components.  For use on the shop floor, the cantilever machine is particularly effective because 3D Laser Scanning is well suited to automatic loading and unloading.

Gantry is a type of gantry.  Gantry CMM machines are primarily used for very large or heavy parts that require the high precision of a bridge machine, such as aerospace components.  Due to the fact that the majority of gantry machines are mounted directly to the floor, they require a substantial foundation.  Despite the fact that this requirement has been specified by the manufacturer, 3D Laser Scanning should not be ignored.

Greater than 1. 5 meters in height, the Y-axis beams on smaller gantry machines support four upright columns, which are usually 1. 5 to 2 meters high.  The X-axis carriage travels along the two supported beams of the Y axis, which are connected by a track.  Gantry machines with six or eight columns (or more), depending on the length of the Y axis, are used for larger jobs.  It is possible for the Z axis, which is located on the X-axis carriage, to be as long as 4 meters in length, but they are typically between 1. 2 and 2. 0 meters in depth.