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Scan results different from keyed-in points

TheBradish
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!Confused 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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  • "keyed in gage points"

    ...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.

    Print is master, but angles are not defined, so I have to use the model for that. After zooming in close, it looks my keyed points are not actually on the model, as you suggest, but scanned points are. Not sure where I went wrong here. After starting a brand new program I have gotten my scans to agree with keyed in points (or at least much closer).

    I am assuming you have a manual align and DCC align? maybe the part was moved.

    could it be that you have probe comp OFF? .018 is .5mm

    I did to manual and DCC. Part was not touched during this process. I kept re-measuring and got the same divergent results.
    Probe Comp is ON. (If only it could be so simple...)
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  • "keyed in gage points"

    ...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.

    Print is master, but angles are not defined, so I have to use the model for that. After zooming in close, it looks my keyed points are not actually on the model, as you suggest, but scanned points are. Not sure where I went wrong here. After starting a brand new program I have gotten my scans to agree with keyed in points (or at least much closer).

    I am assuming you have a manual align and DCC align? maybe the part was moved.

    could it be that you have probe comp OFF? .018 is .5mm

    I did to manual and DCC. Part was not touched during this process. I kept re-measuring and got the same divergent results.
    Probe Comp is ON. (If only it could be so simple...)
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