Orientation ( GD&T)

ORIENTATION – ANGULAR RELATIONSHIPS OF FLAT SURFACES Training By Kishor Bhatia

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ORIENTATION DEFINITION Orientation refers to the angular relationship, which exists between two or more lines, surfaces, or other features. SYMBOLS FOR GEOMETRIC CHARACTERISTICS. ANGULARITY

PERPENDICULARITY

PARALLELISM

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ANGULARITY WITHOUT DATUM IDENTIFICATION SYMBOLS

Angularity is the condition of a surface, center plane, or axis at a specified angle from a datum plane or axis.

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APPLICATION

The angle between the datum and the controlled features should be stated as the basic angle  It should be enclosed in a rectangular frame to indicate that the general tolerance note does not apply. The angle may also be specified as the rate of taper, by means of a note, such as BASIC TAPER 0.25 PER mm. 4

TOLERANCE ZONES – SURFACES

 The tolerance zone for an angularity, perpendicularity, and parallelism tolerance is the space between two parallel planes separated by the specified tolerance and related to the datum by the basic angle. All points on the controlled surface must be contained within this space. 5

TOLERANCE ZONES – SURFACES PERPENDICULARITY

DEFINITION Perpendicularity is the condition of a surface, center plane, or axis at a right angle to a datum plane or axis. 6

PARALLELISM

DEFINITION

Parallelism equidistant equidistant planes or a

is the at all along datum

condition of a surface, center plane, points from a datum plane; or axis at its length from one or more datum axis. 7

ORIENTATION TOLERANCING OF FLAT SURFACES DRAWING SPECIFICATION

Fig shows three simple parts in which one flat surface is designated as a datum feature and another flat surface is related to it by one of the orientation tolerances. 8

INTERPRETATION

Each of these tolerances are interpreted to mean that the designated surface shall be contained within a tolerance zone consisting of the space between two parallel planes separated by the specified tolerance (0.05mm), and related to the datum by the basic angle specified (30, 90,or 0). 9

MEASURING PRINCIPLES

The part to be measured is set up on a surface plate in such a way that the surface of the part, were it perfectly formed, would be parallel with the surface plate or with an auxiliary square or angle plate. When necessary a sine-bar or an angle plate is used. An indicator gage is used to measure from the surface or angle plate. 10

PRINCIPLE OF INTER RELATIONSHIP

When an orientation tolerance is specified there is no need to specify a form tolerance for the same feature unless a smaller tolerance is necessary.

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SIMILAR SURFACES

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CONTROL IN TWO DIRECTIONS

It may be functionally more important to measure the angle in a direction parallel to a side or perpendicular to the front or back face. In this case one side or face must be chosen as a secondary datum, as shown in Fig. 13

ORIENTATION – LINES RELATED TO SURFACES

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ORIENTATION – LINES RELATED TO SURFACES The axis or centerline of hole is related by an orientation tolerance to a flat surface. The flat surface is designated as the datum feature.

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TOLERANCE ZONE FOR ANGULARITY INTERPRETATION

The center of the hole must be contained within a tolerance zone consisting of the space between two parallel planes.These planes are separated by a specified tolerance of 0.15mm and are related to the datum. 16

TOLERANCE ZONE FOR PERPENDICULARITY

A cylindrical tolerance zone perpendicular to a datum plane, within which the axis of the considered feature must lie. Diameter of tolerance zone is equal to the specified tolerance. Every point on the centerline of the hole falls within the tolerance zone. 17

MEASURING PRINCIPLE - ANGULARITY

A gaging mandrel is fitted in the hole. The part set upon a surface plate, using a sine bar of the basic angle. An indicator gage is used to measure the distance from the top of the mandrel to the surface plate. Indicator readings are then noted at positions A and B. 18

MEASURING PRINCIPLE - PERPENDICULARITY

V = (d R) /D V = Variation in orientation of the hole, which must not exceed the specified tolerance. d = Depth of hole. D = Length between indicator reading positions R = Difference between indicator readings. 19

MEASURING PRINCIPLE - PARALLELISM

B

A

A gaging mandrel is fitted in the hole. An indicator gage is used to measure the distance from the top of the mandrel to the surface plate. Indicator readings are then noted at positions A and B. 20

CONTROL OF DIRECTION OF ANGULARITY

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MEASURING PRINCIPLE

Fig 1

Fig 3

Fig 2

Two separate measurements have to be made,as in Fig 1 and Fig 2, where the part is clamped to a square angle plate. 22

CONTROL OF PARALLELISM IN TWO DIRECTIONS

If control with a side is also required, the side should be designated as a secondary datum. The tolerance zone will be a parallelepiped, and two separate measurements are to be made.

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CONTROLS ON MMC BASIS

As a hole is a feature of a size any of the tolerances can be modified on MMC basis. The symbol of MMC m is added after the tolerances. 24

MEASURING PRINCIPLE

On MMC basis feature can be checked with fixed GO gages, rather than measuring instruments

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ORIENTATION OF EXTERNAL CYLINDRICAL FEATURES CONTROL OF CENTER LINES Orientation of the centerline of a feature are applied to drawings.

Perpendicularity is considered to apply in all directions, unless a note is added such as THIS DIRECTION ONLY or DIRECTION OF ARROW ONLY. 26

INTERPRETATION

The center line of the cylindrical feature must be contained within a tolerance zone consisting of the space between two parallel planes separated by the specified tolerance, as shown in Fig. This tolerance is 0.1 mm. As the tolerance planes for perpendicularity can be revolved around the feature axis the tolerance zone effectively becomes a cylinder .The diameter of this cylinder is equal to the specified tolerance. 27

MEASURING PRINCIPLE

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ORIENTATION USING LINES AS DATUMS

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ORIENTATION USING LINES AS DATUMS INTREPRETATION WHEN MMC IS NOT SPECIFIED The tolerance zone is always the space between two parallel planes separated by the specified tolerance and related to the datum by the basic angle. For Perpendicularity and parallelism, either the part or the tolerance zone can be revolved without affecting the angular relationship. Two or more separated measurements must then be made to ensure that the tolerance is met in all positions or directions. It may be found that the resulting tolerance zones effectively become a cylinder of the same diameter as the specified tolerance.

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MEASURING PRINCIPLES WHEN MMC IS NOT SPECIFIED

The part is mounted on a surface plate, using an angle plate of basic angle where necessary, in such a way that the feature or surface requiring control is in a horizontal position. If the datum feature refers to line elements of a cylindrical surface, the datum for an external cylindrical feature is a flat surface on which the feature rests. For an internal cylindrical surface the part is supported on a mandrel slightly smaller than the actual diameter of the feature. 31

ORIENTATION USING LINES AS DATUMS

MEASURING PRINCIPLE ANGULARITY OF FLAT SURFACE WITH AN EXTERNAL CYLINDER. 32

INTERNAL CYLINDRICAL FEATURE

The part must be rotated around this datum axis to a position where the difference in readings over the entire surface is at its minimum. In this position the full indicator movement measured over the surface represents the angularity error. 33

PARALLELISM OF A FLAT SURFACE WITH A CYLINDRICAL HOLE

The part is then rotated to a position where the difference in indicator reading across the surface of the part is at a minimum. The extreme difference in reading over the whole surface with the part in this position constitutes the parallelism error. 34

PERPENDICULARITY OF A HOLE WITH LINE ELEMENTS OF A SURFACE

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ANGLARITY OF A HOLE WITH AN EXTERNAL CYLINDER

The tolerance zone is the space between two parallel planes, 0.08 mm apart related to the datum by the specified angle. 36

MEASURING PRINCIPLE FOR A HOLE WITH AN EXTERNAL CYLINDER

For measuring purposes the feature is supported in an encircling ring on a suitable angle plate. The hole is fitted with a gaging mandrel and the part is then aligned so that the indicator reading at “A” is at a minimum in relation to the reading at “B”.

Indicator readings are then taken and corrected for the length of hole as explained for the part shown in Fig. 37

ANGULARITY WITH TWO HOLES AS PRIMARY DATUM

For measurement purposes the controlled hole is fitted with a gaging mandrel. Indicator readings are then taken over the mandrel and corrected for length of hole. 38

PARALLELISM OF HOLES

V = ( d R ) /D

where:

V = Variation in orientation of the hole, which must not exceed the specified tolerance. d = Depth of hole. D = Length between indicator reading positions

R = Difference between indicator readings. 39