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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. Part 1 : Grasping the “ Basics ”. 1.00±0.01. 2.00±0.01. The Part. 1.99.

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Notice

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.

Understanding True Position


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Part 1 : Grasping the “Basics”

Understanding True Position


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1.00±0.01

2.00±0.01

The Part

Understanding True Position


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1.99

2.01

1.01

0.99

1.00±0.01

2.00±0.01

The Tolerances

Understanding True Position


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1.01

Part 1 Center

Part 2 Center

0.99

1.99

2.01

The Tolerance Zone

Understanding True Position


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1.01

Part 1 Center

Part 2 Center

0.99

1.99

2.01

The Question… Which Part is Better?

Understanding True Position


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1.01

Part 1 Center

0.99

1.99

2.01

Part 1 is within the tolerance zone, but…

Understanding True Position


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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

Understanding True Position


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

Understanding True Position


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1.99

2.01

1.01

Part 1 Center

Part 2 Center

0.99

Use a Circle instead of a Square!

Understanding True Position


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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.

Understanding True Position


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Mathematically Speaking….

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


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Diametral Zone

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


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Ø 0.01 A B C

A

1.00

2.00

B

C

Here’s an Example Calculation

Understanding True Position


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Ø 0.01 A B C

A

Actual Measurements:

X=2.003

Y=1.004

1.00

2.00

B

C

CAN WE SHIP IT?

Understanding True Position


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Actual X = 2.003Actual Y=1.004

Basic X=2.000Basic Y=1.000

Δ X = 0.003 Δ Y = 0.004

TP = 0.0032+0.0042 * 2or

TP = 0.009+0.016 * 2or

TP = 0.025 * 2or

TP = .005 * 2 so…..

Understanding True Position


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True Position = 0.010

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


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YES, WE CAN!

Ø 0.01 A B C

A

Our True Position is within the Specification….

Barely!

1.00

2.00

B

C

Understanding True Position


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Let’s do this very example in Calypso and see if the math works out!

Understanding True Position


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Understanding True Position


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

Understanding True Position


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It Works!

Understanding True Position


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Ø 0.01 A B C

A

1.00

2.00

B

C

Same Print, this time a “Real” Part

Understanding True Position


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On a “Real” Part:

X= 1.9619

Y= 1.0081

Understanding True Position


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Actual X = 1.9619Actual Y = 1.0081

Basic X = 2.000Basic Y = 1.000

Δ X = -0.0381 Δ Y = 0.0081

TP = -0.03812+0.00812 * 2or

TP = 0.0015+0.0001 * 2or

TP = 0.0016 * 2or

TP = .0390 * 2 so…..

Understanding True Position


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True Position = 0.0779

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


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What???

Understanding True Position


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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!

Understanding True Position


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Let’s see how this changes things.

Understanding True Position


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Understanding True Position


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Watch out for Outliers!

Understanding True Position


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Understanding True Position


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Now that we have that sorted out,

ONE MORE TIME!

X= 1.9504

Y= 1.0104

Understanding True Position


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Actual X = 1.9504Actual Y = 1.0104

Basic X = 2.000Basic Y = 1.000

Δ X = -0.0496 Δ Y = 0.0104

TP = -0.04962+0.01042 * 2or

TP = 0.0025+0.0001 * 2or

TP = 0.0026 * 2or

TP = .0507 * 2 so…..

Understanding True Position


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True Position = 0.1014

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


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YES!!!

Understanding True Position


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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?”

Understanding True Position


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Turn on Additional Position Result in the Characteristic Settings Editor.

Understanding True Position


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You’ve got Questions, We have answers.

Understanding True Position

Part 1 : Grasping the “Basics”

Understanding True Position


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