In CMM-Manager 3.9, various improvements were made to the display of the tolerance bar graph in reporting.  This was to clarify in/out of tolerance indications for non-symmetrical tolerances. 

The example shown  above uses a print nominal of 77.5, a (print) tolerance of -0.800 to -0.200, and actual inspection values of 76.650, 76.850, 77.000, 77.150, and 77.350 to result in a report with output indicating Out Of Tolerance minus, -50% of tolerance, middle of tolerance (‘perfect’ part), +50% of tolerance, and Out Of Tolerance plus.

CMM-Manager traditionally treated the tolerance graph as a literal representation of the tolerance definition plotted with zero at the center of the graph. It did not matter if the tolerance was symmetrical, non-symmetrical, or even single sided. The center of the graph was always zero. This could lead to confusion about the meaning of the graph, even though technically the graph was correct.

The above output for POINT 3 from 3.8 SP1 shows a value that represents a ‘perfect’ part. The value is at the

center of the tolerance band. However, the graph seems to indicate that we are trending toward our

negative limit. This is not the case.

That is because the graph is configured as shown above. The graph indeed indicates that the actual value is at the center of the tolerance band.

The text numbers are correct. The graph is correct. However, it appears at first glance to show a negative trending value.

Beginning with CMM-Manager 3.9, the tolerance graph is now centered on the specified tolerance band, whether it is symmetrical, non-symmetrical, or single sided. The middle of the graph is the value that is halfway between the LoTol and UpTol. This means that any actual value that is toward the UpTol from the midpoint will now show a color bar going to the right and any actual value that is toward the LoTol from the midpoint will show a color bar going to the left, which is a much more clear visual indicator of the inspection result.

This is the same output as shown earlier, but in CMM-Manager 3.9. The ‘perfect’ part now shows no bar in the graph since the actual value is at exactly the center target.

Using the above indicated tolerance band of -0.800 to -0.200, the center value would be -0.500. The graph limits would be as shown here. Now anything that is toward UpTol from center will display a bar to the right, and anything that is toward LoTol will display a bar to the left.

The method of determining graph limits is consistent for all tolerance ranges. A range of -0.400 to +0.200 would result in graph limits of -0.400, -0.100 (center), and +0.200.

Please refer to the large comparison picture at the top of the article to see example of minus Out Of Tolerance, -50% of tolerance, at tolerance, +50% of tolerance, and plus Out Of Tolerance.

If you look at the text for Dev(iation) in the Inspection Report above, you will note that the ‘perfect’ part shows a deviation of -0.500. This is correct. This is per-print. This is what the inspection report must reflect. However, this does not help the machine operator adjust the machine.

CMM-Manager offers a very simple solution to this. Using the same measurement results, the results can be reported multiple times using different tolerances and nominals.

The first method is to simply report each feature twice. Once per-print, and once with manually adjusted nominal values and tolerance values in the same Default Report. This will result in a Default Report that contains both results. This may not be desirable in a single report.

If that is the case, simply create two additional reports in the report tab – Inspection Report and Machine Report. Then, copy the appropriate outputs from the Default Report (which contains all reported values) to the correct report. At the end of the inspection, print both reports. Give the Inspection Report to the Engineer, and the Machine Report to the operator.