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Does Translating The Trihedron Ruin "True Zero"?

Hello All!

I'm having a debate with a fellow programmer today on the effects of moving the trihedron away from the CAD's zero point.

This is in reference to a True Position measurement of a hole located at X0 Y14.5.


So there are two different methods to get our alignments and then dimension the true position:

Method 1
"Locate" The Part, by tapping a point on X, Translating the trihedron to that point, tapping a point on Y, Translating the trihedron to that point, etc for Z.

This obviously moves the trihedron around a bunch, and because of that physical features need to be used on the part to "return" the trihedron back to X0, Y0, Z0 on the drawing for the true position measurement to be taken.

Method 2
Leave the trihedron at X0, Y0, Z0 of the CAD model and NEVER translate it. Instead, tap points around the part and align without ever moving the trihedron.


Now, once dimensioned, both of these methods give me the same Nominal Measurement Values, X0, Y14.5.

Both of these methods use the same features to create their Iterative and Best Fit alignments.

Is there any difference in the end?

Please let me know if that wasn't clear enough, and thanks in advance for any help!
Parents
  • If the cad model is built to the drawing sometimes they will use other co-ordinate systems i.e. Wing system instead of part and they will build from there and then rotate to a part system after. This means in catia a hole might be X 14.00453 Y 20.00764 Z 10.000. but the drawing will only be to 2 decimal places. Therefore if you translate to said hole and then offset back drawing values as round number ( X14, Y20, Z10. you wont end up at the exact original co-ordinate and could put errors into rotations or other features. drawings are very commonly rounded up decimal places. In reality you need either the original 3d data or tabulation data i.e. Anvil,Cadd5,catia ect.
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  • If the cad model is built to the drawing sometimes they will use other co-ordinate systems i.e. Wing system instead of part and they will build from there and then rotate to a part system after. This means in catia a hole might be X 14.00453 Y 20.00764 Z 10.000. but the drawing will only be to 2 decimal places. Therefore if you translate to said hole and then offset back drawing values as round number ( X14, Y20, Z10. you wont end up at the exact original co-ordinate and could put errors into rotations or other features. drawings are very commonly rounded up decimal places. In reality you need either the original 3d data or tabulation data i.e. Anvil,Cadd5,catia ect.
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