gdt-true position

Application Seminar 2006

Geometric Dimensioning & Tolerancing

True Position

Carl Zeiss IMT GD&TApplication Seminar 2006

Page 2

GD&T

• Rules

• Use and effect of Material Condition Modifiers

• Datum Reference Frame mobility sources

• Comparison between the traditional and new methods

Page 3

GD&TEarlier generation software

“…. in early generation software packages, the result with MMC is identical to the result without MMC - the actual tolerance will be bigger than the original given tolerance, which means it is easier to be qualified for the evaluated object. So ….users will be happy with the result within the tolerance ….”

Page 4

GD&TUse and effect of MCMs

Material Condition Modifier (MCM) MMC/LMC/RFS are used to define the treatment of size deviations

MCM expand the tolerance zone depending on the considered feature and they mobilize the tolerance zone depending on the datum features

MCM for the considered featureM: expands the tolerance zoneS: size does not influence the tolerance zoneL: expands the tolerance zone

MCM for datum featuresM: gives mobility to the tolerance zoneS: means static tolerance zoneL: gives mobility to the tolerance zone

Mobility of the tolerance zone reduces the actual deviation

Page 5

Page 6

Page 7

Page 8

“Mobility” of the tolerance zone is

the freedom to perform a best fit to

attempt to accept the work piece.

Page 9

GD&TGeneral rules for the handling of DRFs

Längenmessabweichung E

GD&T takes fit and function of the imperfect objects into consideration

Datum reference frames (DRFs) are simulated by perfect inverse datum features with nominal orientation

DRFs eliminate up to three degrees of rotational- and three degrees of translational degrees of freedom

The order of the datum features in the feature control frame specifies the order of adaption to the work piece

If a datum feature can and may eliminate a degree of freedom, it must

Datum features with size shall be fixed at virtual material condition or if specified regardless of features size consume all the space available in- or outside

Page 10

Page 11

Page 12

Page 13

Page 14

Datum features with size shall be fixed at virtual material condition or if specified regardless of features size consume all the space available inside or outside

Page 15

GD&TExamples w/o MMC

Längenmessabweichung EA

BC

0,02 M A B M C M

Page 16

BC

0,02 M A B M C M

Page 17

BC

0,02 M A B M C M

Page 18

BC

0,02 M A B M C M

Incr

ea

sed

M

ob

ility

0,02 M A B M C M

Without best fit the distance

between datum features is

not taken into account!

This is the reason, why the

result with MMC sometimes

is larger than without (GO /

NO GO like a hard gage).

Page 19

GD&TDRF mobility sources

Datum features referenced with MMC or LMC

An inadequate number of datum features to eliminate all degrees of freedom

The second and all lower tiers of a composite feature control frame

Unstable datum features (e.g. convex reference plane)

0,1 A B C M

Static DRF

Highly mobile DRFSlightly mobile DRF

0,4 A B C 0,2 A B 0,1 A

C

B

A

Page 20

GD&TComparison between the methods

Early generation s/w method:

Alignment based on the datum features

MCM for the considered feature expands the tolerance zone

MCM for datum features expands the tolerance zone

Page 21

GD&TComparison between the methods

Correct Method (Calypso):

Best fit based on the previously described rules with a virtual gauge

MCM for datum features gives mobility and does not expand the tolerance zone

Bestfit reduces the deviation of the actuals

Bestfit is limited by the MCM bonus

Traditional method:

Alignment based on the datum features

MCM for datum features expands the tolerance zone

Page 22

Result with Calypso: Out of Tolerance

Actual = 0,72 mm Exp. Tol.= 0,7 mm

x xx

GD&TComparison example 1

Nominals: Actuals:X1 = -39,64Y1 = 0D1 = 20,20X2 = 0Y2 = 0D2 = 30,10X3 = +39,64Y3 = 0D3 = 20,20

B

40 40

30 ±0,1 CA 0,3 M A B M C

2x 20 ±0,2

Page 23

Result with Calypso: Out of Tolerance

x xx

B

40 40

30 ±0,1 CA

1 2 3

0,3 M A B M C 2x 20 ±0,2

Page 24

0,3 M A B M C

Tolerance Zone / MMC with Calypso: Result:Out of Tolerance

B

40 40

30 ±0,1 CA

1 2 3

2x 20 ±0,2

x xx

X

Y

Page 25

0,3 M A B M C

B

40 40

30 ±0,1 CA

1 2 3

2x 20 ±0,2

x xx

X

Y

Tolerance Zone / MMC with Calypso: Result:Out of Tolerance

Page 26

Result with Traditional: In Tolerance

B

40 40

30 ±0,1 CA

1 2 3

x xx

0,3 M A B M C 2x 20 ±0,2

Page 27

B

40 40

30 ±0,1 CA

1 2 3

0,3 M A B M C 2x 20 ±0,2

x xx

X

Y

Tolerance Zone / MMC with Traditional S/W: Result:In Tolerance

Page 28

B

40 40

30 ±0,1 CA

1 2 3

0,3 M A B M C 2x 20 ±0,2

Tolerance Zone / MMC with Traditional S/W: Result:In Tolerance

Actual = 0,72 mm Exp. Tol.= 0,90 mmx xx

X

Y

Page 29

0,3 M A B M C

Nominals: Actuals:X1 = -40,00Y1 = 0,45D1 = 20,20X2 = 0Y2 = 0D2 = 30,10X3 = +40,00Y3 = 0,45D3 = 20,20

B

40 40

30 ±0,1 CA

1 2 3

2x 20 ±0,2

x x

x X

Y

Tolerance Zone / MMC with Calypso: Result:In Tolerance

Page 30

0,3 M A B M C

B

40 40

30 ±0,1 CA

1 2 3

2x 20 ±0,2

x x

x X

Y

Tolerance Zone / MMC with Calypso: Result:In Tolerance

Page 31

B

40 40

30 ±0,1 CA

1 2 3

0,3 M A B M C 2x 20 ±0,2

x

X

Y x

Page 32

B

40 40

30 ±0,1 CA

1 2 3

0,3 M A B M C 2x 20 ±0,2

Tolerance Zone / MMC with Traditional: Result:In Tolerance

x

X

Y x

Sometimes the conclusion from

either method is identical

....despite different

actuals and different

expanded tolerances!

Sometimes the conclusion from

either method is identical

....despite different

actuals and different

expanded tolerances!

gdt-true position

Documents

tolerance zone mcm

tolerance zone mobility

tolerance zone s

static tolerance zone

actual tolerance

original given tolerance

datum features mcm

considered feature