Scan results different from keyed-in points

I have a part with a very tight profile tolerance (form+location) of .0005. I wrote a program with a model and aligned to all 3 datums.

I keyed in gage points and read the vectors from the model. Part is out of tolerance (which I expected) by about .001, the profile being off center.

Next I added a linear TTP scan along the same section where I probed the gage points. The scan shows deviations up to .018!

Same program, same part, same alignment.

What could I be doing wrong with my scan to get a result that differs so much from my keyed-in points?

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Matthew D. Hoedeman over 10 years ago

"keyed in gage points"

These points MAY not lie exactly on the cad data. Don't just find the vectors, FIND the entire point. Pcdmis will take keyed in values and find the closest CAD XYZ nominals.

If the PRINT is master (I assume this is where the gage points come from), then don't use the cad for nominals. If the cad is master and the gage points on the print are 'target' points, only use cad nominals.

Also, I seriously doubt that they gave you a list of gage points as close together as the scan points will be, so that comparison is apples to donkey carts.
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Matthew D. Hoedeman over 10 years ago

"keyed in gage points"

These points MAY not lie exactly on the cad data. Don't just find the vectors, FIND the entire point. Pcdmis will take keyed in values and find the closest CAD XYZ nominals.

If the PRINT is master (I assume this is where the gage points come from), then don't use the cad for nominals. If the cad is master and the gage points on the print are 'target' points, only use cad nominals.

Also, I seriously doubt that they gave you a list of gage points as close together as the scan points will be, so that comparison is apples to donkey carts.
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