True Position calculations

[[Ch...]]

Does this TP value seem correct? Can someone explain the 'direction' parameter in the position box under 'datums"?

Changing the direction to XY seems to help but holes far from zero always give crazy TP values even when deviations are not too bad. I had an engineer tell his team to ignore all positional values coming from me because they aren't accurate. He said it seemed like Z axis was being factored in... but he only wants the XY coords to factor in for positional? What can I do to solve this?

Thank you all very much

 

[[Ch...]]

The direction parameter allows you to orientate the tolerance zone. In your case the tolerance zone is perpendicular to the X' direction of the datum system located in the given distance in Y' and Z' direction from the origin of the datum system. 

Note X', Y' and Z' have nothing to do with direction in the global coordinate system but with the direction of the datum system. X' is that direction from the datum system that have the smallest angle to the global X direction.

This is very old concept (it cames from 2007) and in the meanwhile the ISO have introduced orientation planes to achieve the same thing. Therefore in current software version you will find instead orientation planes to avoid confusion.

First thing you can try is to check if the direction parameter is causing you problems. Please set for testing purposes your tolerance zone to spherical. If then your results as expected you have choosen a wrong direction parameter.

Otherwise I would assume that the big difference is caused from the used datum system. Before you can compare "classical X, Y or Z" check with the results from a positional tolerance you have to bring all in the same alignment.

Reason for this is that according to ISO standards the tolerance zone have to orientated to actual datum system using the nominal value estimated from the nominal datum system.

Therefore (if not done already), please create a alignment from coordinate system using the datum system as coordinate system. If my assumption is correct X', Y' or Z' values should be much higher.

If this is not explaining the difference please contact your local partner because we will need to have a deeper look into your project.

[[Jo...]]

Hi, 

I think you are using an alignment to calculate XYZ, and another alignment (ABC) to calculate the true position.

[[DW...]]

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I am spit balling here, but first change your standard to "Geometry". We can change it later. Then, verify your datum reference frame is set up correctly. You need to know exactly what directions (XY, YZ, whatever) your positions are being calculated from. We can help you with more information (screenshots). From there, change the true value from nominal element to user defined. Using your drawing, manually type in the correct coordinates. Its not possible to tell given the snippets you've provided, so we would need more information.