Perpendicularity of cylinder

Hi everyone,

I am new to the forum and by searching the topics I couldn't find the answer to my question.
I need to measure the perpendicularity of a hollow cylinder according to its planar surface used as datum. I have used two different approaches in this regard, but I obtain very different results.
in the first approach, I measure 5 circles at different levels along the cylinder height [using auto circle feature] then I construct a cylinder from these 5 circles [constructed feature] and finally I chose Perpendicularity Dimension to measure the perpendicularity.
in the second approach, I use Auto Cylinder feature[using Adaptive Cylinder Concentric Circle Scan] to construct the cylinder geometry as showed in the attached image, where the scans are performed at the same positions along the axis compare to the previous approach. by measuring the perpendicularity according to the same datum as the first approach, this time I get perpendicularity values which are much worst than the previous case. [in first case I get 0.006 mm while in second case it is 0.098mm].
I would appreciate if you can help me find out which of these two approach is correct, or is there a better solution to measure the perpendicularity precisely?

Thank you in advance.

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AndersI over 7 years ago

in the first approach, I measure 5 circles at different levels along the cylinder height [using auto circle feature] then I construct a cylinder from these 5 circles [constructed feature]
...
in the second approach, I use Auto Cylinder feature[using Adaptive Cylinder Concentric Circle Scan] to construct the cylinder geometry

An (non-)obvious difference between those methods is that for the constructed cylinder, the length will be the actual span of the hits, while for the autocylinder the length will be taken from the CAD surface(s) involved. As you can never put actual hits over all of a surface, this will always generate a smaller perpendicularity value for the constructed (or measured) cylinder, compared to the autocylinder, even if you construct a cylinder from the autocylinder's hit points!

Using the (P) option in the FCF, you can tell PC-DMIS the computation length explicitly, to eliminate this difference.
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AndersI over 7 years ago

in the first approach, I measure 5 circles at different levels along the cylinder height [using auto circle feature] then I construct a cylinder from these 5 circles [constructed feature]
...
in the second approach, I use Auto Cylinder feature[using Adaptive Cylinder Concentric Circle Scan] to construct the cylinder geometry

An (non-)obvious difference between those methods is that for the constructed cylinder, the length will be the actual span of the hits, while for the autocylinder the length will be taken from the CAD surface(s) involved. As you can never put actual hits over all of a surface, this will always generate a smaller perpendicularity value for the constructed (or measured) cylinder, compared to the autocylinder, even if you construct a cylinder from the autocylinder's hit points!

Using the (P) option in the FCF, you can tell PC-DMIS the computation length explicitly, to eliminate this difference.
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