1. Understanding True Position
NOTICE :
This presentation was given at the October 2007 “Lunch N Learn” at Ellison Technologies in Charlotte.
The presentation is meant to be viewed with the narration and detailed explanation of the presenter.
Last Updated: 8/27/2014
Understanding True Position

2. Understanding True Position
Part 1 : Grasping the “Basics”
Last Updated: 8/27/2014
Understanding True Position

3. Understanding True Position
1.00±0.01
2.00±0.01
The Part
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Understanding True Position

4. Understanding True Position
1.99
2.01
1.01
0.99
1.00±0.01
2.00±0.01
The Tolerances
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Understanding True Position

5. Understanding True Position
1.01
Part 1 Center
Part 2 Center
0.99
1.99
2.01
The Tolerance Zone
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Understanding True Position

6. Understanding True Position
1.01
Part 1 Center
Part 2 Center
0.99
1.99
2.01
The Question… Which Part is Better?
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Understanding True Position

7. Understanding True Position
1.01
Part 1 Center
0.99
1.99
2.01
Part 1 is within the tolerance zone, but…
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Understanding True Position

8. Understanding True Position
1.01
Part 2 Center
0.99
1.99
2.01
Part 2 is closer to the Nominal Center and will assemble easier than Part 1
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Understanding True Position

9. Understanding True Position
How can we set up a tolerance band that fairly and functionally judges the position of features?
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Understanding True Position

10. Understanding True Position
1.99
2.01
1.01
Part 1 Center
Part 2 Center
0.99
Use a Circle instead of a Square!
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Understanding True Position

11. Understanding True Position
Definition Time!!!
The result of a True Position Characteristic is the diameter of a circle, centered on the basic dimensions from the specified datums, that contains the actual center point.
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Understanding True Position

12. Understanding True Position
Mathematically Speaking….
True Position = ΔX ΔY * 2
ΔX = Difference from Basic X value from Actual X value
ΔY = Difference from Basic Y value from Actual Y value
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Understanding True Position

13. Understanding True Position
Diametral Zone
Tolerance
True Position
Ø A B C
No Tolerances A
Primary, Secondary, Tertiary Datums
1.00
2.00 B C
New Part Print w/True Position
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Understanding True Position

14. Understanding True Position
Ø A B C A
1.00
2.00 B C
Here’s an Example Calculation
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Understanding True Position

15. Understanding True Position
Ø A B C A
Actual Measurements:
X=2.003
Y=1.004
1.00
2.00 B C
CAN WE SHIP IT?
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Understanding True Position

16. Understanding True Position
Actual X = Actual Y=1.004
Basic X= Basic Y=1.000
Δ X = Δ Y = 0.004
TP = * 2 or
TP = * 2 or
TP = * 2 or
TP = * 2 so…..
Last Updated: 8/27/2014
Understanding True Position

17. Understanding True Position
Hole Center from Nominal
0.005
True Position Result = 0.010
0.004
0.003
Nominal Center at X=2, Y=1 from Basic Dimensions
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Understanding True Position

18. Understanding True Position
Ø A B C A
Our True Position is within the Specification….
Barely!
1.00
2.00 B C
YES, WE CAN!
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Understanding True Position

19. Understanding True Position
Let’s do this very example in Calypso and see if the math works out!
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Understanding True Position

20. Understanding True Position
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Understanding True Position

21. Understanding True Position
This is a Theoretical feature with X Y coordinates placed exactly at and
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Understanding True Position

22. Understanding True Position
It Works!
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Understanding True Position

23. Understanding True Position
Ø A B C A
1.00
2.00 B C
Same Print, this time a “Real” Part
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Understanding True Position

24. Understanding True Position
On a “Real” Part: X= Y=
Last Updated: 8/27/2014
Understanding True Position

25. Understanding True Position
Actual X = Actual Y =
Basic X = Basic Y = 1.000
Δ X = Δ Y =
TP = * 2 or
TP = * 2 or
TP = * 2 or
TP = * 2 so…..
Last Updated: 8/27/2014
Understanding True Position

26. Understanding True Position
Hole Center from Nominal
0.0390
0.0081
0.0381
True Position Result =
Nominal Center at X=2, Y=1 from Basic Dimensions
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Understanding True Position

27. Understanding True Position
What???
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Understanding True Position

28. Understanding True Position
Explanation Time!!!
The GD&T standard specifies that the FUNCTIONAL center be used for calculations. This means for a hole, that the Maximum Inscribed fit be used. Calypso does this automatically!
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Understanding True Position

29. Understanding True Position
Let’s see how this changes things.
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Understanding True Position

30. Understanding True Position
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Understanding True Position

31. Understanding True Position
Watch out for Outliers!
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Understanding True Position

32. Understanding True Position
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Understanding True Position

33. Understanding True Position
Now that we have that sorted out,
ONE MORE TIME! X= Y=
Last Updated: 8/27/2014
Understanding True Position

34. Understanding True Position
Actual X = Actual Y =
Basic X = Basic Y = 1.000
Δ X = Δ Y =
TP = * 2 or
TP = * 2 or
TP = * 2 or
TP = * 2 so…..
Last Updated: 8/27/2014
Understanding True Position

35. Understanding True Position
Hole Center from Nominal
0.0507
0.0104
0.0496
True Position Result =
Nominal Center at X=2, Y=1 from Basic Dimensions
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Understanding True Position

36. Understanding True Position
YES!!!
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Understanding True Position

37. Understanding True Position
ONE MORE THING…..
You might say :
“So if True Position only gives me distance from center, how do I know how to make my offsets?”
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Understanding True Position

38. Understanding True Position
Turn on Additional Position Result in the Characteristic Settings Editor.
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Understanding True Position

39. Understanding True Position
You’ve got Questions, We have answers.
Understanding True Position
Part 1 : Grasping the “Basics”
Last Updated: 8/27/2014
Understanding True Position