GD&T Position Calculation

[[ca...]]

Hello everyone,

I am trying to inspect the position of holes but have a problem to calculate the deviations in X and Y directions aligned with position computation.

In addition to the pre-alignment, I used RPS alignment and local best-fit for main alignment. Although I can see the true position coordinates correctly in the check position window, computed position value much bigger than it must be according to position formula ( 2 x (dx^2 + dy^2)^1/2) .Coordinate system that I used is constructed with 3-2-1 method (referencing RPS points)

Could you help me to figure out what is wrong with the methodology that I followed?

Thanks,

Canset

 

 

[[Na...]]

Hello cansetm,

the GD&T check is calculated according to the Standard. It might use another point selection than in the measuring principle fitting element, e.g. fitting element with all points instead of 3 sigma etc. The used datum system and alignment has to be the same, too. For a deeper analysis with your specific project please reach out to your local distributor. 

Regards,
Nanno

[[ca...]]

Hello Nanno,

Thanks for the help. I think the problem caused from the local best-fit which is a child alignment of RPS. RPS alignment directly referenced from datum target points which creates the datum system  for position calculation. Just like you mentioned when I make the datum system and alignment  same, the problem is gone.

One last question, when we use RPS alignment, we use global coordinate system as datums and when we compare and use the formula with the deviation in X and Y axis, the result generally matches with the position calculation.  Just wanted to ask if does it make sense or not?

Thanks,

Canset

Edited April 21, 2023