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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.

Understanding True Position

Part 1 : Grasping the “Basics”

Understanding True Position

Part 1 Center

Part 2 Center

0.99

1.99

2.01

The Question… Which Part is Better?

Understanding True Position

Part 1 Center

0.99

1.99

2.01

Part 1 is within the tolerance zone, but…

Understanding True Position

Part 2 Center

0.99

1.99

2.01

Part 2 is closer to the Nominal Center and will assemble easier than Part 1

Understanding True Position

How can we set up a tolerance band that fairly and functionally judges the position of features?

Understanding True Position

1.99 functionally judges the position of features?

2.01

1.01

Part 1 Center

Part 2 Center

0.99

Use a Circle instead of a Square!

Understanding True Position

Definition Time!!! functionally judges the position of features?

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.

Understanding True Position

Mathematically Speaking…. functionally judges the position of features?

True Position = ΔX2 + ΔY2 * 2

ΔX = Difference from Basic X value from Actual X value

ΔY = Difference from Basic Y value from Actual Y value

Understanding True Position

Diametral Zone functionally judges the position of features?

Tolerance

True Position

Ø 0.01 A B C

No Tolerances

A

Primary, Secondary, Tertiary Datums

1.00

2.00

B

C

New Part Print w/True Position

Understanding True Position

Ø 0.01 A B C functionally judges the position of features?

A

1.00

2.00

B

C

Here’s an Example Calculation

Understanding True Position

Ø 0.01 A B C functionally judges the position of features?

A

Actual Measurements:

X=2.003

Y=1.004

1.00

2.00

B

C

CAN WE SHIP IT?

Understanding True Position

Actual X = 2.003 Actual Y=1.004 functionally judges the position of features?

Basic X=2.000 Basic Y=1.000

Δ X = 0.003 Δ Y = 0.004

TP = 0.0032+0.0042 * 2 or

TP = 0.009+0.016 * 2 or

TP = 0.025 * 2 or

TP = .005 * 2 so…..

Understanding True Position

True Position = 0.010 functionally judges the position of features?

Hole Center 0.005 from Nominal

0.005

True Position Result = 0.010

0.004

0.003

Nominal Center at X=2, Y=1 from Basic Dimensions

Understanding True Position

YES, WE CAN! functionally judges the position of features?

Ø 0.01 A B C

A

Our True Position is within the Specification….

Barely!

1.00

2.00

B

C

Understanding True Position

Let functionally judges the position of features?’s do this very example in Calypso and see if the math works out!

Understanding True Position

Understanding True Position functionally judges the position of features?

This is a Theoretical feature with X Y coordinates placed exactly at 2.003 and 1.004.

Understanding True Position

It Works! exactly at 2.003 and 1.004.

Understanding True Position

Ø 0.01 A B C exactly at 2.003 and 1.004.

A

1.00

2.00

B

C

Same Print, this time a “Real” Part

Understanding True Position

Actual X = 1.9619 Actual Y = 1.0081 exactly at 2.003 and 1.004.

Basic X = 2.000 Basic Y = 1.000

Δ X = -0.0381 Δ Y = 0.0081

TP = -0.03812+0.00812 * 2 or

TP = 0.0015+0.0001 * 2 or

TP = 0.0016 * 2 or

TP = .0390 * 2 so…..

Understanding True Position

True Position = 0.0779 exactly at 2.003 and 1.004.

Hole Center 0.0390 from Nominal

0.0390

0.0081

0.0381

True Position Result = 0.0779

Nominal Center at X=2, Y=1 from Basic Dimensions

Understanding True Position

What??? exactly at 2.003 and 1.004.

Understanding True Position

Explanation Time!!! exactly at 2.003 and 1.004.

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!

Understanding True Position

Let exactly at 2.003 and 1.004.’s see how this changes things.

Understanding True Position

Understanding True Position exactly at 2.003 and 1.004.

Watch out for Outliers! exactly at 2.003 and 1.004.

Understanding True Position

Understanding True Position exactly at 2.003 and 1.004.

Now that we have that sorted out, exactly at 2.003 and 1.004.

ONE MORE TIME!

X= 1.9504

Y= 1.0104

Understanding True Position

Actual X = 1.9504 Actual Y = 1.0104 exactly at 2.003 and 1.004.

Basic X = 2.000 Basic Y = 1.000

Δ X = -0.0496 Δ Y = 0.0104

TP = -0.04962+0.01042 * 2 or

TP = 0.0025+0.0001 * 2 or

TP = 0.0026 * 2 or

TP = .0507 * 2 so…..

Understanding True Position

True Position = 0.1014 exactly at 2.003 and 1.004.

Hole Center 0.0507 from Nominal

0.0507

0.0104

0.0496

True Position Result = 0.1014

Nominal Center at X=2, Y=1 from Basic Dimensions

Understanding True Position

YES!!! exactly at 2.003 and 1.004.

Understanding True Position

ONE MORE THING….. exactly at 2.003 and 1.004.

You might say :

“So if True Position only gives me distance from center, how do I know how to make my offsets?”

Understanding True Position

Turn on Additional Position Result in the Characteristic Settings Editor.

Understanding True Position

You Settings Editor.’ve got Questions, We have answers.

Understanding True Position

Part 1 : Grasping the “Basics”

Understanding True Position

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