understanding true position with mmc in calypso zeiss... · for each case, the gd&t control...

Understanding True Position

with MMC

in Calypso

Last Updated: 9/15/2014 True Position with MMC 1

This presentation shows how MMC applied to features and datums effect the calculation and evaluation of True Position characteristics.

For each case, the GD&T control frame for the True Position, Calypso characteristic window and Calypso custom printout to go with each True Position, and an explanation of each result is shown.


The Print:

C

B

-A-

A True Position Tolerance is given to this hole with MMC applied to feature and datums.

Ø 1.0 ± 0.1 typ 3 places

10.0


Feature Actuals and True Position Callout:

C

B

-A-X=0Y=10D=1

X=0Y=0D=1

X=10.1Y=0D=1


Ø 0.1 A B C

10.0


Calypso Report:Calypso Characteristic:


Why the Answer?:

10.0

The result for True Position can be thought of as the diameter of a circle, centered at the target (basic dimensions), that contains the actual center.

-B- Center

-C- Center

X

Y

10.1

Feature Actual

Center

Feature Target

Center

True Position Result = Ø 0.2

True Position Tolerance = Ø 0.1


Ø 0.1 M A B C


C

B

-A-X=0Y=10D=1

X=0Y=0D=1

X=10.1Y=0D=1


10.0


Why the Answer?:

10.0

When MMC is applied to the Feature, the Tolerance Band grows by the amount of the bonus.

(bonus = actual Ø – smallest allowable Ø for a hole at MMC)

-B- Center

-C- Center

X

Y

10.1

Feature Actual

Center

Feature Target

Center

True Position Result = Ø0.2

True Position Tolerance with

Bonus = Ø 0.2


Ø 0.1 A B M C


C

B

-A-X=0Y=10D=1

X=0Y=0D=1

X=10.1Y=0D=1


10.0


Why the Answer?: When MMC is applied to the Centering Datum, the coordinate system center can move within a circle centered at the actual datum center, with a diameter of the bonus. In this case, the Y axis must go through the exact center of the clocking datum, since no MMC is applied there.

-B- Center

-C- Center

Feature Actual

Center

Feature Target

Center


True Position Tolerance = Ø0.1

““““Bonus”””” on Center Ø 0.1


Ø 0.1 A B C M


C

B

-A-X=0Y=10D=1

X=0Y=0D=1

X=10.1Y=0D=13


10.0


Why the Answer?:

10.0

When MMC is applied to the clocking datum and not the centering datum, the origin of the coordinate system cannot change. The rotation, however, can change, so the Y axis passes through the bonus circle around the clocking datum’s center.

Since Rotation does not bring the feature center closer to the target center, the answer is the same as if no MMC is applied at all.

-B- Center

-C- Center

X

Y

10.1

Feature Actual

Center

Feature Target

Center

True Position Result = Ø0.2True Position Tolerance = Ø

0.1

““““Bonus”””” on Clocking Ø 0.1


Ø 0.1 A B M C M


C

B

-A-X=0Y=10D=1

X=0Y=0D=1

X=10.1Y=0D=1


10.0


Why the Answer?:

10.0

-B- Center

-C- Center

X

Y

10.05

Feature Actual

Center

Feature Target

Center


True Position Tolerance = Ø0.1

When MMC is applied to the Centering Datum and the Clocking Datum, the Coordinate system is free to rotate and translate within the constraints of the bonus circles centered on both datums. The Coordinate system can move half of the datum bonus amount toward the feature center.




Ø 0.1 M A B M C M


C

B

-A-X=0Y=10D=1

X=0Y=0D=1

X=10.1Y=0D=1


10.0


Why the Answer?:

10.0

When MMC is applied to the Feature and Datums, all mobility of the Coordinate system discussed in previous slides apply, plus there is a larger overall tolerance zone for the feature. Calypso will “bestfit” until either the true position result is within tolerance, or the result cannot be improved further.

-B- Center

-C- Center

X

Y

10.075

Feature Target

Center


True Position Tolerance with

Bonus = Ø 0.2



Feature Actual

Center


understanding true position with mmc in calypso zeiss... · for each case, the gd&t control...

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