213n456-2 - comments of germany

7/31/2019 213N456-2 - Comments of Germany

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German Comment on ISO CD 5459-3ISO/TC 213 N 443 & ISO/TC 213/WG 2 N 158

The aim of datum targets is to define a set of small supports of theretically exact form,orientation and location relative to each other on which the workpiece can rest unique in

orientation and location without any further constraint. Orientation and location oftolerance zones are related to the set of datum targets.

In order to keep the workpiece in a unique orientation and location the number and thelocation of the datum targets must be chosen according to the degrees of freedom of theworkpiece.

A realisation of the datum targets may be small supports in a manufacturing orinspection device.

Clause 5 of the CD does not meet this philosophy. 5.1 requires filtration, 5.3 requires

that the associated ideal feature is of the same invariance class as the correspondingnon-ideal feature. For the use of datum targets, there shall be no filtration. The selectionof datum targets is a kind of filtration in itself. The associated feature, e.g. 2 points in aplane associated to a cylindrical feature as secondary datum, see figures 3 and 4, andthe datum feature may be of different invariance classes (plane and cylinder in figure 3and 4).

For clause 5 of ISO 5459-3 we propose the following content:

ISO/TC 213 N 456-2


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ISO 5459-3Proposal

5 Datum targets

5.1 General

A datum target is a point or straight line or limited small area of a plane on which theworkpiece feature can rest.

Datum targets can be used to establish a single datum or a common datum or a datumsystem.

Datum target systems define a set of datum targets (small supports) of theretically exactorientation and location relative to each other on which the workpiece can rest unique in

orientation and location without any further constraint. Orientation and location oftolerance zones are related to the set of datum targets.

The relationship between the datum targets is given by theoretically exact dimensions.

The real feature is contacting the datum targets.

Thereby datum targets define situation features (plane, straight line, point) to which theorientations or locations of toleranced features are related, e.g. on a casting to definethe position (orientation and location) of the first machined surfaces forming the datumsystem of the final machined part.

5.2 Operations

5.2.1 Extraction

For the extraction method see 4.1.

5.2.2 Filtration

Using datum targets there is no filtration.

5.2.3 Association

The datum targets shall be associated to the extracted feature. The objective function forthe association is to contact the extracted feature.

The number and the location of the datum targets relative to each other shall be definedaccording to the 6 degrees of freedom of the workpiece.


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In cases of rigid workpieces less or more datum targets lead to an unstable location ofthe workpiece and shall be avoided.

For the specification of datums composed of datum targets there are the following 2methods:

a) to define the targets where each target reduces one degree of freedom, see figures 1to 7.

b) to define the targets where a set of targets define a centre point, see figures 8 and 9.

The number of datum targets for a datum target system is 6 in case a) and 6 + n in caseb) where n is:

1 for a secondary cylinder in the datum system, see figure 82 for a primary cylinder in the datum system, see figure 9.

Fig. 1: 6 datum targets for a datum system of plane-plane-plane

Fig. 2: 6 datum targets for a datum system of plane-plane-plane, drawing indication

Fig. 3: 6 datum targets for a datum system of plane-cylinder-plane

Fig. 4: 6 datum targets for a datum system of plane-cylinder-plane, drawing indication

Fig. 5: 6 datum targets for a datum system of cylinder-plane-plane

Fig. 6: 6 datum targets for a datum system of plane-cylinder-plane

Fig. 7: 6 datum targets for a datum system of cylinder-plane-plane

Fig. 8: 7 datum targets for a datum system of plane-cylinder centre point-plane

Fig. 9: 8 datum targets for a datum system of cylinder centre points-plane-plane


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6 Fixed Points, Primary Plane

HENZOLD

25 - 025

X

Z

Y

6 fixed points determine location and orientation in space


5/12

Datum TargetsHENZOLD

31 - 247

ISO 1101, ISO 5459

datum targets (areas) A1, A2, A3 establish

datum targets (lines) B1, B2 establish

datum target (point) C1 establishes

primary datum

secondary datum

tertiary datum

A

B

C

5A3

5A1

5A2

5B1

5B2

5C1

0,6 M A B CC

A

B

A1, 2, 3

B1, 2

C1


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6 Fixed Points, Secondary Cylinder

HENZOLD

29 - 206

X

Z

Y

6 fixed points determine the location and orientation in space


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Datum Targets

Relationship to Toleranced Feature

HENZOLD

31 - 180

ISO 5459

C

B

A

B2

0,1 A B C

A1, 2, 3

B1, 2

C1

A2 A3

B1A1

C1

B1 B2

C1

datum targets A1, A2, A3 establish

datum targets B1, B2 establish

datum target c1 establishes

primary datum

secondary datum

tertiary datum

A

B

C


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6 Fixed Points, Primary Cylinder

HENZOLD

31 - 245

X

Z

Y

6 fixed points determine the location and orientation in space


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6 Fixed Points, Secondary Cylinder

HENZOLD

25 - 029

X

Z

Y



10/12

6 Fixed Points, Primary Cylinder

HENZOLD

31 - 202

X

Z

Y



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Datum TargetsPoint of an Axis as Secondary Datum HENZOLD29 - 205

X

Z

Y

3 points determine the location of the axis7 points determine the location and orientation of the part

ASME Y14.5


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Datum TargetsPoints of Common Axis as Primary Datum HENZOLD31 - 246

X

Z

Y

6 points determine the location of the axis8 points determine the location and orientation of the part

ASME Y14.5

213n456-2 - comments of germany

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