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: 8/27/2014Understanding True Position1

Part 1 : Grasping the “Basics” Last Updated: 8/27/2014Understanding True Position2

2.00± ±0.01 The Part Last Updated: 8/27/2014Understanding True Position3

2.00± ±0.01 The Tolerances Last Updated: 8/27/2014Understanding True Position4

The Tolerance Zone Part 1 Center Part 2 Center Last Updated: 8/27/2014Understanding True Position5

The Question… Which Part is Better? Part 1 Center Part 2 Center Last Updated: 8/27/2014Understanding True Position6

Part 1 is within the tolerance zone, but… Part 1 Center Last Updated: 8/27/2014Understanding True Position7

Part 2 is closer to the Nominal Center and will assemble easier than Part 1 Part 2 Center Last Updated: 8/27/2014Understanding True Position8

How can we set up a tolerance band that fairly and functionally judges the position of features? Last Updated: 8/27/2014Understanding True Position9

Part 1 Center Part 2 Center Use a Circle instead of a Square! Last Updated: 8/27/2014Understanding True Position10

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. Last Updated: 8/27/2014Understanding True Position11

Mathematically Speaking…. True Position = ΔX 2 + ΔY 2 * 2 ΔX = Difference from Basic X value from Actual X value ΔY = Difference from Basic Y value from Actual Y value Last Updated: 8/27/2014Understanding True Position12

New Part Print w/True Position No Tolerances Ø 0.01 A B C A B C True Position Diametral Zone Primary, Secondary, Tertiary Datums Tolerance Last Updated: 8/27/2014Understanding True Position13

Here’s an Example Calculation Ø 0.01 A B C A B C Last Updated: 8/27/2014Understanding True Position14

CAN WE SHIP IT? Ø 0.01 A B C A B C Actual Measurements: X=2.003 Y=1.004 Last Updated: 8/27/2014Understanding True Position15

Actual X = 2.003Actual Y=1.004 Basic X=2.000Basic Y=1.000 Δ X = Δ Y = TP = * 2or TP = * 2or TP = * 2or TP =.005 * 2 so….. Last Updated: 8/27/2014Understanding True Position16

True Position = Hole Center from Nominal True Position Result = Nominal Center at X=2, Y=1 from Basic Dimensions Last Updated: 8/27/2014Understanding True Position17

Ø 0.01 A B C A B C Our True Position is within the Specification…. Barely! YES, WE CAN! Last Updated: 8/27/2014Understanding True Position18

Let’s do this very example in Calypso and see if the math works out! Last Updated: 8/27/2014Understanding True Position19

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This is a Theoretical feature with X Y coordinates placed exactly at and Last Updated: 8/27/2014Understanding True Position21

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Same Print, this time a “ Real ” Part Ø 0.01 A B C A B C Last Updated: 8/27/2014Understanding True Position23

On a “Real” Part: X= Y= Last Updated: 8/27/2014Understanding True Position24

Actual X = Actual Y = Basic X = 2.000Basic Y = Δ X = Δ Y = TP = * 2or TP = * 2or TP = * 2or TP =.0390 * 2 so….. Last Updated: 8/27/2014Understanding True Position25

True Position = Hole Center from Nominal True Position Result = Nominal Center at X=2, Y=1 from Basic Dimensions Last Updated: 8/27/2014Understanding True Position26

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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! Last Updated: 8/27/2014Understanding True Position28

Let’s see how this changes things. Last Updated: 8/27/2014Understanding True Position29

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Watch out for Outliers! Last Updated: 8/27/2014Understanding True Position31

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Now that we have that sorted out, ONE MORE TIME! X= Y= Last Updated: 8/27/2014Understanding True Position33

Actual X = Actual Y = Basic X = 2.000Basic Y = Δ X = Δ Y = TP = * 2or TP = * 2or TP = * 2or TP =.0507 * 2 so….. Last Updated: 8/27/2014Understanding True Position34

True Position = Hole Center from Nominal True Position Result = Nominal Center at X=2, Y=1 from Basic Dimensions Last Updated: 8/27/2014Understanding True Position35

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“So if True Position only gives me distance from center, how do I know how to make my offsets?” ONE MORE THING….. You might say : Last Updated: 8/27/2014Understanding True Position37

Turn on Additional Position Result in the Characteristic Settings Editor. Last Updated: 8/27/2014Understanding True Position38

Understanding True Position You’ve got Questions, We have answers. Part 1 : Grasping the “Basics” Last Updated: 8/27/2014Understanding True Position39