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What is a CMM Machine?

A Coordinate Measuring Machine (CMM) is a common find in the metrology lab of many manufacturing facilities. They serve as a method to perform dimensional analysis and are important to ensure a part’s quality. In this article, we’ll discuss what a CMM is, the benefits and drawbacks of using CMM, and alternatives to CMM.

What is a CMM?

A CMM is a metrology tool used to measure the dimensions of an object. It does this by touching a probe to a point on the part’s surface and recording its cartesian coordinates. Dozens or even hundreds of points are measured on a part and used to verify critical dimensions. As the selected points are collected, the CMM translates these points into usable data for comparing measurements to the original design drawing or CAD file. Parts can also be reverse engineered from the results of a CMM’s data.

There are several different types of CMM’s, such as bridge, gantry, horizontal arm, articulated arm, and cantilever. However, they all consist of the same basic components: a base, a computer, and a touch probe. The base of a CMM acts as a table for the part to be measured. These bases are built to be flat, smooth, and stable so the part will not move and cause inaccuracies in the collected data. The computer serves as the brain of the machine where it can be manually controlled or programmed to run the touch probe. This is also where the data points and measurements are recorded and calculated. Lastly, the touch probe is a smooth ball at the end of a stylus. Whenever this makes contact with the part, it signals to the computer to record its location in 3-dimensional space. For some CMM’s, the touch probe diameter and stylus length can be changed to allow the probe to reach more difficult areas of the part.

Benefits of Using CMM

CMM has many benefits, which mainly stem from its programmability. CMM’s are able to be manually operated or programmed via Computer Numerical Control (CNC). This enables high precision because it removes the possibility of human error. An operator can program the machine to take the measurements needed and leave it unattended while the process is completed. Additionally, programming the machine to run automatically is helpful when measuring multiple identical parts for part inspection and quality assurance. The same coordinates can be measured on each piece with the same process to ensure uniformity.