Both of these standards define the test methodology for evaluating the measuring performance of Coordinate Measuring Machines. The ASME B89.1.4b-2001 standard has been superseded by ASME B89.4.10360.2-2008, rendering it obsolete.
What is the difference between them?
- There are many, but the main difference between the two standards is that they require different test measurements to evaluate the performance of the CMM.
- ASME B89.1.4b-2001 requires multiple measurements of a ball bar at various positions and orientations on the CMM. The range of the 3D distances between the spheres on the ball bar are compared to the volumetric specification. Limitations of this method include:
- The distance between the spheres is not calibrated, so the volumetric results cannot be compared to SI units
- The length of the ball bar is determined by the shortest axis on the CMM, which in most cases is not a suitable length to properly test the longer axes of the CMM. In these cases the CMM is measured in smaller sections, but doing so can disguise some geometry errors.
- There is no standard ball bar pattern that must be performed by all technicians, so the measurements taken varies between technicians, O.E.M.s and service providers.
- Linear errors are only measured in line with each axis. The logic being that if the volumetric geometry is good, and the linear accuracy is good then both together must also be good, although it is not tested.
- ASME B89.4.10360.2-2008 requires multiple measurements of 5 different lengths in various defined orientations on the CMM. Improvements over the older method include:
- The artefact must be calibrated, so all measurements can be compared to SI units
- The lengths measured varies, to ensure that optimal lengths for each measuring run are taken. Longer axes are checked over a longer distance.
- The position and orientation of all measurements is well defined, which removes much of the variation in results between technicians, O.E.M.s and service providers
- Both linear and geometry errors are represented in all of the measurements
- The tests defined in the newer standard make it more sensitive at detecting measuring errors on the CMM. Simply put, it’s a more thorough test of geometry errors on a CMM. It does however, take longer to perform the calibration.
Can I just order a calibration to the ASME B89.1.4b-2001 instead?
- Yes you can. We suggest using the current standard to evaluate your machine, but ultimately the choice is up to you. However, aside from the obvious benefit of evaluating your CMM to a more thorough test there are other considerations as well. Calibrating your CMM to an obsolete standard may be of particular concern if your company operates under a registered Quality Management System.