Instructions for the Use of CMM Probes

Coordinate measuring machines (CMMs) are efficient and high-precision measuring instruments that emerged and developed in the mid-20th century. They have been widely used in various industries to measure the dimensions of basic parts or components. The basic principle is to place the object in the measuring space of the CMM and measure the specific positions of the object surface points. The basic shape and position of the object are then calculated from the coordinates of these points.

1. Precautions for using CMM  probes

The probe is a very important component of the CMM. Here is a brief description of its basic components. The probe is primarily used to directly contact the surface of a workpiece. During contact, the mechanical device of the probe will shift and produce a corresponding signal, which ultimately forms good measurement data.

Generally, the probe is composed of a rod and a ruby ball. The ruby ball usually has a very high hardness to ensure that there is minimal wear during use, resulting in ideal measurement accuracy and effectiveness.

In the measurement process using the CMM, it is first necessary to ensure that the probe's shape and rigidity are ideal, to maximize the measurement accuracy of the CMM.

In addition to this, there are several issues to be aware of when using the CMM:

Firstly, the probe should be as short as possible to avoid its bending or tilting.

Therefore, when measuring with the CMM, choosing the shortest possible probe within permissible conditions can greatly enhance the measurement accuracy.

The second point is to minimize connection points. This is mainly because the connection between the probe and the extension rod of the CMM will introduce additional potential bending or deformation points, making the probe more vulnerable to damage during use. Therefore, it is necessary to minimize the number of connections as much as possible.

The last point to emphasize is that the probe's ball should be as large as possible. This requirement is based on two considerations: Firstly, a larger ball can maximally reduce the gap between the ball and the rod, thus effectively reducing the triggering caused by ball shaking. Secondly, a larger ball diameter can reduce the impact of surface polishing on measurement accuracy. Overall, taking precautions while using CMM touch probes will ensure the accuracy and lifespan of these critical machine tools.

2. Repeatability of Measuring Probes 

During the measurement process using the CMM, the sampling direction of the CMM probe stylus should be perpendicular to the probe body to obtain the best measurement results. Therefore, during the measurement process, efforts should be made to maintain consistency between the sampling direction and the probe body, to obtain the best measurement efficiency.

If sampling is conducted in the state of parallelization between the sampling direction of the probe body and the probe, then the repeatability of CMM measurement using the probe will be significantly reduced. The third scenario is when there is a certain angle between the sampling direction of the probe body and the probe. It is neither parallel nor perpendicular. The measurement accuracy obtained in this scenario is also less than that in a perpendicular state, and it is basically impossible to achieve repeated measurements. Therefore, efforts should be made to avoid this scenario as much as possible when using the CMM for measurements.