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Ballbar Testing 101

June 9th, 2014

Ballbar calibration can unveil a number of machine tool problems.

Canadian Industrial Machinery (CIM) asked Philip Smith, technical sales manager for Renishaw Canada, to explain the function of ballbars.

CIM: What is a ballbar?

One end of the ballbar mounts via a magnetic cup onto the machine table, while the ball at the other end attaches to a magnetic cup in the machine’s spindle. These mountings create a three-point kinematic location. 

 

CIM: How does it work?

 The heart of the ballbar is a highly accurate (1-µm) optical linear scale with very high resolution (0.1 µ). As the ballbar’s length changes due to slight machine inaccuracies, the optical scale measures what are hoped to be tiny linear displacement changes. This streaming linear displacement data is transmitted back to a computer, which is running the ballbar software.

After the test is complete, the software compiles this data and then calculates 22 machine criteria. For instance, we can look at backlash, squareness, and machine positional capability.

 

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