True Position inspection

[bootnreboot]

Does anybody have a source showing inspection methods for determining True Position ?
I teach GD&T classes and am always asked..."How are parts inspected for true position?"
I know there are many ways to check this but i can not find actual examples of how a virtual condition fixture is being used, CMM or other gauges.
Thank you in advance for any help you can send my way.

 

[cloa]

Try a cross link for the GD&T forum

 

[mwisnefsky]

The best book I've found on GD&T is this:

http://www.amazon.com/gp/product/0872638650

I think this would normally be done with a Faro or Romer arm.

But True Position can be inspected with normal linear measurements. True position is just a different way of allowing tolerance. Measure the position of the hole in the normal X & Y dimensions, the square root of [(error in x)^2 + (error in y)^2] is the amount of true position tolerance used.

Example:
-True position within .060 inches
-Nominal Position is (1,3), Actual Position is (1.023,2.981)
-Square Root[(.023)^2 + (.019)^2] = [0.000529 + 0.000361]^.5 = .0298
-Of the .060 inches of available tolerance, you have used .0298

If you're referring to a fixture, it depends on the callout - Maximum Material Condition or Regardless of Feature Size.