• Author / Uploaded
• Mahender Kumar

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ANSI And ISO Geometric Tolerancing Symbols There are several standards available worldwide to describe the symbols and the rules. These are American Society of Mechanical Engineers, ASME Y14.5M-2009, (GD&T - Geometric Dimensioning and Tolerancing) and International Organization for Standardization, ISO/TC 213, (GPS - Geometrical Product Specification) and ISO/TC 10 Technical Product Documentation (see the ISO GPS Specifications and verification List). The ISO (GPS) standards are typically only address a single topic at a time.ISO/TC 213 is a technical committee that standardizes tolerancing and related metrological practices. ASME Y14.5M standard has the advantage of providing a fairly complete set of standards for GD & T in one document.

Geometric Tolerancing Reference Chart ASME Y14.5M And ISO/TC 213 Datum Needed

Applicable Modifiers (RMS, LMC, MMC)

Straightness

No

LMC or MMC can apply to feature of size

Form

Flatness

No

Does not apply

Form

Circularity

No

Does not apply

Form

Cylindricity

No

Does not apply

Profile

Line Profile

No

Does not apply

Profile

Surface Profile

No

Does not apply

Orientation

Perpendicularity

Yes

LMC or MMC can apply to feature of size

Orientation

Angularity

Yes

LMC or MMC can apply to feature of size

Orientation

Parallelism

Yes

LMC or MMC can apply to feature of size

Tolerances

Characteristics

Form

Symbols

Location

Symmetry

Yes

RFS always

Location

Positional

Yes And No

LMC or MMC can apply to feature of size

Location

Concentricity

Yes

RFS always

Runout

Circular Runout

Yes

RFS always

Runout

Total Runout

Yes

RFS always

Additional Geometric Tolerancing Symbol Chart ASME Y14.5M And ISO/TC 213 Description

Symbols

References

Max Material Condition (MMC)

ISO 2692/ASME

Least Material Condition (LMC)

ISO 2692/ASME

Regardless Of Feature Size (RFS)

ISO/ASME

Spherical Diameter (SD)

ISO/AMSE

Radius

ISO/ASME

Diameter

ISO/ASME

Envelope Requirement

ISO/ASME

Free State Condition(Non Rigid Parts)

ISO 10579/ASME

Minor Diameter

ISO/ASME

Major Diameter

ISO/ASME

Pitch Diameter

ISO/ASME

Common Zone

ISO/ASME

Exact Dimension

ISO/ASME

Dimension Origin

ISO/ASME

All Round (Profile)

ISO NONE/ASME

Datum Feature Indication

ISO/ASME

Datum Target Indication

ISO 5459

Projected Tolerance Zone

ISO 10578/ASME

Geometric Dimensioning And Tolerancing Reading Geometric Dimensioning And Tolerancing reading is very important to understand detailed drawings. It helps to read drawings for engineers, designers, manufacturers etc. what surface has to be machined carefully. Geometric tolerancing reading helps to understand to specify and control the form, location and orientation of the features of components and manufactured parts. Geometric Dimensioning and Tolerancing is an efficient method for describing the tolerancing mandated by the designer of the part. The Datum axis or Datum planes are to be used for locating other features. With GD&T all inspection will result in the same result. It will help to understand if the dimension is within or out of tolerance. Geometric Dimensioning and Tolerancing forces the designers to totally consider functions, manufacturing processes, and inspection methods. These explanations would be good answers to why GD&T should be used. Chosen geometric tolerance and modifier/modifiers will be shown in Tolerance Feature Indication/Feature Control Frame. Tolerance control frame is a rectangular symbol which contain indications that define the geometrical tolerance for features. Geometric Tolerance defines the form and the size of a tolerance zone. Tolerance zone may be one of the followings; the area within circle, the space between two coaxial cylinders, the area between two parallel lines, the space within a cylinder, the

space between two parallel surfaces or two parallel planes the space within a geometrically a square or rectangular prism or a solid with six faces, the area between two concentric circles,

Tolerance Feature Indication/Feature Control Frame Symbol.

Primary Datum, Secondary Datum, and Tertiary Datum Planes: Datums must be perpendicular to each other.

Primary Datum Plane: The primary datum is selected to provide functional relationships, standardizations and repeatability between surfaces. A standardization of size is desired in the manufacturing of a part. Consideration of how parts are orientated to each other is very important. The chosen primary datum must insure precise measurements.

Secondary Datum Plane: Secondary datums are produced perpendicular to the primary datum so measurements can be referenced from them.

Tertiary Datum Plane: Tertiary datum is always perpendicular to both the primary and secondary datums ensuring a fixed position from three related parts.

Understanding of Geometric Tolerancing Modifiers The Modifiers (MMC,LMC,RFS) are used to clarify implied tolerances. There are three directly implied modifiers to the tolerance value. These are; 1-) Regardless of Feature Size (RFS) 2-) Maximum Material Condition (MMC) 3-) Least Material Condition (LMC)