ZEISS Styli for Coordinate Measuring Machines

The standard accuracy of the probe ball is Grade 5. For form measurements with higher accuracy, balls with better roundness are needed to minimize errors in the measurement. Note, however, that Grade 3 balls are not necessarily better than Grade 5 balls, because the grade of the probe balls is determined in a batch process. So, if a particular manufacturing batch selection is in tolerance, it is assumed that all balls are within that grade. The accuracy distribution of the balls thus corresponds to a Gaussian distribution. That is why poorer ball accuracies may also be sold in Grade 3.

If you need a styli with very accurate roundness, you should use a styli with a certificate. Only then you can be sure that the specified roundness is maintained and meets your requirements.

A styli, like any other tool, is subject to natural wear and tear. Damage, e.g., by abrasion, scratches or chipping, or contamination, e.g., by material application, oil or paint, significantly affect the measuring accuracy. Since this is usually not visible to the bare eye, the styli should be checked under a microscope for damage or contamination. How often you should perform this inspection depends on the styli's application or the environmental parameters.

We recommend getting an overview by means of a kind of tool card, as it is also available for production machines, and to determine an inspection cycle from it.

How long you can use your styli depends entirely on the type of application. Wearing occurs where the probe ball touches the workpiece being measured. If the same point is always used, for example when scanning a plane, then the styli will have a shorter life than if circles are scanned, for example. This is because the entire equator of the sphere is in use. Other factors that affect styli life include scanning distance, speed, probing force, measuring environment, and the material being measured.

We recommend that you create a quality card for each styli and use it to test the styli on a regular basis. This will provide a reliable average life of the particular styli over time.

If a collision occurred, the stylus system should be checked on a ring. Since these are high-precision measuring devices, one should not take any risks. Special attention should be paid to styli or extensions with a carbon fiber shaft, as it is possible that individual fibers have been torn. This can only be detected on the ring itself. Styli with a carbide or ceramic shaft can still be used after a collision if the ball is still on the shaft.

Caution: Extreme care must be taken with dovetailed balls! In contrast to the case of glued or soldered balls in a shaft, the balls do not necessarily fall off in a mortised connection. They can remain loose on the trunnions and lead to measurement errors. Unfortunately, this often happens unnoticed, so you should check dovetailed balls immediately after a collision.

If there is a contact between the workpiece and the styli shaft instead of the probe ball, there is a shaft touching. Since a shaft touching also triggers a signal at the probe head, but is not defined, shaft touching leads to incorrect measurements that often go unnoticed. When measuring with small probe balls, which usually have thin shafts, there is a risk that the shaft will bend during probing. If the fasteners used, such as angles or cubes, are of poor quality or have been inaccurately adjusted, shaft touching may also occur.

You should pay attention to the following points when planning your stylus system.

The stylus system should

• be as rigid as possible
• have as few connection points as possible
• weigh as little as possible
• have as little thermal expansion as possible

You should also make sure to use high quality components, as the quality of the stylus system pays 100 % into the accuracy of your measurement results.