Understanding True Position

1
Understanding True Position with MMC in Calypso
2
This presentation shows how MMC applied to
features and datums effect the calculation and
evaluation of True Position characteristics. For
each case, the GDT 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.
3
The Print
-A-
C
Ø 1.0 0.1 typ 3 places
A True Position Tolerance is given to this hole
with MMC applied to feature and datums.
B
10.0
4
Feature Actuals and True Position Callout
-A-
X0 Y10 D1
C
Ø 0.1 A B C
Ø 1.0 0.1 typ 3 places
X0 Y0 D1
X10.1 Y0 D1
B
10.0
5
Calypso Report
Calypso Characteristic
6
Why the Answer?
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.
-C- Center
Y
True Position Result Ø 0.2
True Position Tolerance Ø 0.1
Feature Target Center
X
-B- Center
Feature Actual Center
10.0
10.1
7
Feature Actuals and True Position Callout
-A-
X0 Y10 D1
C
Ø 0.1 M A B C
Ø 1.0 0.1 typ 3 places
X0 Y0 D1
X10.1 Y0 D1
B
10.0
8
Calypso Report
Calypso Characteristic
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Why the Answer?
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)
-C- Center
Y
True Position Result Ø 0.2
True Position Tolerance with Bonus Ø 0.2
Feature Target Center
-B- Center
X
Feature Actual Center
10.0
10.1
10
Feature Actuals and True Position Callout
-A-
X0 Y10 D1
C
Ø 0.1 A B M C
Ø 1.0 0.1 typ 3 places
X0 Y0 D1
X10.1 Y0 D1
B
10.0
11
Calypso Report
Calypso Characteristic
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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.
-C- Center
True Position Result Ø 0.1418
Bonus on Center Ø 0.1
True Position Tolerance Ø 0.1
Feature Target Center
-B- Center
Feature Actual Center
10.0
10.0501
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Feature Actuals and True Position Callout
-A-
X0 Y10 D1
C
Ø 0.1 A B C M
Ø 1.0 0.1 typ 3 places
X0 Y0 D1
X10.1 Y0 D1
B
10.0
14
Calypso Report
Calypso Characteristic
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Why the Answer?
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 datums 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.
Bonus on Clocking Ø 0.1
-C- Center
Y
True Position Result Ø 0.2
True Position Tolerance Ø 0.1
Feature Target Center
-B- Center
X
Feature Actual Center
10.0
10.1
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Feature Actuals and True Position Callout
-A-
X0 Y10 D1
C
Ø 0.1 A B M C M
Ø 1.0 0.1 typ 3 places
X0 Y0 D1
X10.1 Y0 D1
B
10.0
17
Calypso Report
Calypso Characteristic
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Why the Answer?
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.
Bonus on Clocking Ø 0.1
-C- Center
Y
True Position Result Ø 0.1
Bonus on Center Ø 0.1
True Position Tolerance Ø 0.1
Feature Target Center
-B- Center
X
Feature Actual Center
10.0
10.05
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Feature Actuals and True Position Callout
-A-
X0 Y10 D1
C
Ø 0.1 M A B M C M
Ø 1.0 0.1 typ 3 places
X0 Y0 D1
X10.1 Y0 D1
B
10.0
20
Calypso Report
Calypso Characteristic
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Why the Answer?
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.
Bonus on Clocking Ø 0.1
-C- Center
Y
True Position Result Ø 0.150
Bonus on Center Ø 0.1
True Position Tolerance with Bonus Ø 0.2
Feature Target Center
-B- Center
X
Feature Actual Center
10.0
10.075