Alexandre Desroches Dimensional Management November 7th 2006 Potential 3DCS problems Features measurements problem with size tolerance combined with Profile or Flatness tolerances. Alexandre Desroches Dimensional Management November 7th 2006

Problem statement: We find a constant feature measurement of –0.03937” between contact surfaces. In theory this number should be 0.0000”. In most aerospace study, errors in the order of 0.040 is not acceptable. Furthermore, when we open the measurement box and click the current button (after a nominal built). It indicates a of 0. This is in contradiction with the simulations which indicates a constant values of –0.03937”. Please refer to the following slides and sent models for more details.

Parts with size and profile tolerances: Used feature moves to position the parts Used feature distance measurement to measure distance between contact surfaces We get a constant value of –0.03937” See attached Case #1 zipped files

Parts with profile tolerance only but with form and orientation equal to profile tolerance value: Used feature moves to position the parts Used feature distance measurement to measure distance between contact surfaces We get a constant value of –0.03937” See attached Case #2 zipped files

Parts with profile tolerance only but with form and orientation equal to profile tolerance value (continued): Additional concern: The base plate was modeled with a nominal thickness 0.5000. Profile tolerance is of .010, therefore thickness should vary between .4950 and .5050. The feature measurement indicates 15.9% rejection (8.3% estimated) which we find quite high.

Parts with size and flatness tolerances: Used feature moves to position the parts Used feature distance measurement to measure distance between contact surfaces We get a constant value of –0.03937” See attached Case #3 zipped files

Collar exercise: Files are available on demand Used feature moves to position the parts. We are clocking the dark blue part surface to a feature point on the light blue part. Used feature distance measurement to measure distance between contact surfaces In this case the nominal value is –0.03937”. We get a constant value of –0.03937”

Questions: Why do we get a constant feature measurement of -0.03937 in these cases? Please explain and provide recommendations to avoid this situation. How come we get should a high out of spec % for the plate thickness when using a simple profile tolerance?