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Readpoints and Alignments..Legacy/Xact

The Rook
I have a few questions and concerns I was hoping could get addressed. So thank you for your insight in advance.

A coworker and I were having a discussion about using the readpoint alignment to inspect a whole part. I said that is not good practice.

Anyway, he did so and inspected a part using just the readpoint. Numbers were coming out ok...so I was a bit confused.

Can you use the readpoint to inspect the whole part? He also said that you dont need to align to datums. That you can pick them up as normal features then when dimensioning something like true position you can just select those features.

This has really thrown me for a loop. This isn't really good practice...right? Shouldnt a basic alignment of the part be conducted after the readpoint to just solidify it a bit more? Then probe the same features again with a few more hits to refine it?

Is it necessary to do this? And one more thing, I've searched high...I've searched low, I still am not sure when folks talk about legacy or exactmeasure. How do I know what mode I'm in? How do I switch between?

Thanks for reading.
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  • Someone please correct me if I'm wrong, but I was under the impression that using GEOTOL indeed does allow you to select datums from a dropdown without being aligned to those exact datums. Obviously the datums have to be measured and defined beforehand, but on a part with multiple datum structures (A|B|C, G|H|F, etc.) you don't have to be aligned to each one individually before dimensioning.

    Correct. They just need to be measured and defined.
  • in reply to bfire85
    BUT, there are (many) cases where NOT measuring features in the correct alignment can throw your numbers off.
    Easiest case to point out is:
    You have an emboss in your part, it has a generous tolerance, say position of 3mm. It is then defined as a datum for other features, specifically a surface profile. That emboss can be 1.5mm off location in any direction, but if your surface profile is 'tight' (say, 0.5 profile) to the emboss, and you measure them in some other alignment, that surface can in reality be in the correct relationship to the emboss, BUT, since you didn't use the emboss as the alignment to measure the surface, you can get bogus values due to probe comp issues among other things. BEST BET is to always measure to the datums used in the FCF for all features.
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  • in reply to bfire85
    BUT, there are (many) cases where NOT measuring features in the correct alignment can throw your numbers off.
    Easiest case to point out is:
    You have an emboss in your part, it has a generous tolerance, say position of 3mm. It is then defined as a datum for other features, specifically a surface profile. That emboss can be 1.5mm off location in any direction, but if your surface profile is 'tight' (say, 0.5 profile) to the emboss, and you measure them in some other alignment, that surface can in reality be in the correct relationship to the emboss, BUT, since you didn't use the emboss as the alignment to measure the surface, you can get bogus values due to probe comp issues among other things. BEST BET is to always measure to the datums used in the FCF for all features.
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