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How Do You Determine a CMM’s Accuracy?

1 December 2015

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SCSI often gets questions about what’s the best brand for a CMM.  We find that the answer should be more focused on accuracy rather than brand. Just because a machine is a certain brand doesn’t necessarily make it the most accurate.  In fact, there are several makes, models, sizes, accuracy specifications, probe configurations, and other factors that can drive the accuracy of any given machine.

How Accurate are SCSI’s CMM Machines?

Brown & Sharpe 15.22.10 PC-DMIS 1500 mm 2200 mm 1000 mm 5+1L/200 microns Waterloo, IA
DEA Global Advantage 20.33.15 PC-DMIS 2000 mm 3300 mm 1500 mm 2.8+3L/1000 microns Waterloo, IA
Brown & Sharpe 12.22.10 PC-DMIS 1200 mm 2200 mm 1000 mm 2.5+3.0L/1000 microns Peoria, IL
Brown & Sharpe 7.10.7 PC-DMIS 700 mm 1000 mm 700 mm 1.9+4.0L/1000 microns Lafayette, IN
† Factory machine specification for accuracy: L = Length in mm of the feature to be checked

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Here’s an example:  A hole has a position tolerence of 0.04mm. The distance to the datum is 200mm. For the inspection of this feature, a CMM with a volumetric length uncertainty of 2.5+3.0L/1000 microns will be used.

Feature Tolerance (mm) Tolerance Requirement (mm) Size/Distance (mm) Machine Uncertainty Required Manufacturer’s Specs Machine Capability
True Position 0.04 0.02 200 0.004 2.8+3L/1000 0.00340
Parallelism 0.02 0.02 200 0.004 2.8+3L/1000 0.00340
Feature Length +/- 0.01 0.02 200 0.004 2.8+3L/1000 0.00340
Diameter +/- 0.01 0.02 200 0.004 2.8+3L/1000 0.00340
Profile of a Surface 0.01 0.01 200 0.002 2.8+3L/1000 0.00340

If you have a specific part you’d like to measure on one of our CMMs, please contact us:

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