Fundamentals Of Geometric Dimensioning And Tolerancing

• Figures have been revised to add a paragraph number(s) in the lower right corner. This notation is provided to assist users in locating the principal paragraph(s) that refers to the illustration.

• All figures have been revised, where applicable, to show the universal International Organization for Standardization (ISO) datum feature symbol being introduced in this issue of the Standard.

• All figures have been revised, where applicable, to remove the RFS symbol, which is no longer necessary.

A3 SECTION 1, SCOPE, DEFINITIONS, AND GENERAL DIMENSIONING

• Added clarification that the definitions, fundamental rules, and practices for general dimensioning that are established in Section 1 apply to coordinate as well as geometric dimensioning methods.

• Revised the designation from ANSI to ASME to reflect The American Society of Mechanical Engineers as the preparing organization. References to the Standard shall now state ASME Y14.5M-1994.

• Added the following references and sources:

ANSI/ASME B1.2-1983, Gages and Gaging for Unified Inch Screw Threads ANSI B4.4M-1981, Inspection of Workpieces ANSI B5.10-1981, Machine Tapers — Self Holding and Steep Taper Series

ANSI B92.1-1970. Involute Splines and Inspection, Inch Version

ANSI B92.2M-I980, Metric Module, Involute Splines

ASME Y1.1-1989, Abbreviations — For Use on Drawings and in Text

ASME Y14.3M-1994, Multiview and Sectional View Drawings

ASME Y14.5.1M-1994, Mathematical Definition of Dimensioning and Tolerancing Principles ANSI Y14.6aM-1981, Screw Thread Representation (Metric Supplement)

ANSI Y14.7.1-1971, Gear Drawing Standards — Part 1: For Spur, Helical, Double Helical, and Rack

ANSI Y 14.7.2-1978, Gear and Spline Drawing Standards — Part 2: Bevel and Hypoid Gears ASME Y14.8M-I989, Castings and Forgings ANSI/IEEE 268-1992. Metric Practice

• Definitions and terms have been enhanced by expansion, addition, clarification, and reorganization.

• New or revised terms and definitions:

boundary, inner boundary, outer datum feature simulator datum, simulated dimension envelope, actual mating feature feature, axis of feature, center plane of feature, derived median plane of feature, derived median line of feature of size plane, tangent resultant condition true geometric counterpart virtual condition

The term size has been expanded to give more explicit meaning and application to the following: size, actual size, actual local size, actual mating size, nominal size, resultant condition size, virtual condition

Fundamental rules added:

Unless otherwise specified, all dimensions and tolerances apply in a free state condition except as specified under certain conditions as described in Section 6.

Unless otherwise specified, all geometric tolerances apply for full depth, length, and width of the feature.

Dimensions and tolerances apply only at the drawing level where they are specified. A dimension specified for a given feature on one level of drawing (for example, a detail drawing) is not mandatory for that feature at any other level (for example, an assembly drawing).

Paragraph and subparagraph numbering is revised to accommodate new and rearranged text. Subparagraph headings are added to identify subject matter more clearly. Some subparagraphs are condensed into preceding paragraphs for clarity and flow of subject matter.

Explanation and use of leader lines is expanded and clarified.

Dimensions "not to scale" coverage is expanded to accommodate differing methods of drawing preparation from manual to computer graphics systems for product definition.

Explanation of round holes and application of a depth dimension is expanded and clarified in text and illustrations.

Explanation of counterbored holes is expanded and clarified in text and illustrations.

For methods of specifying requirements peculiar to castings and forgings, a reference to ASME Y14.8M is added.

To replace words on the drawing, symbology, as described in Section 3 and Appendix C, is included in the figures.

• New figures are added to expand coverage on "Counterbored Holes" and "Countersunk and Counterdrilled Holes."

• Expansion of figures for "Countersink on a Curved Surface" is provided.

A4 SECTION 2, GENERAL TOLERANCING AND RELATED PRINCIPLES

• Notation is made that if CAD/CAM database models are used and they do not include tolerances, then tolerances must be expressed outside of the database to reflect design requirements.

• Notation is made that tolerances on dimensions that locate features of size are preferably specified by the positional tolerancing method described in Section 5. However, in certain cases, such as locating irregular-shaped features individually or in patterns, the profile tolerancing method as described in Section 6 may be used.

• Clarified and expanded the meaning of implied 90° center lines and surfaces of a part as depicted on engineering drawings versus the meaning of implied 90° basic dimensions when geometric controls are specified.

• The number of decimal places to be used in a dimension and associated tolerances for unilateral, bilateral, basic, or limit dimensioning is presented for both metric or inch applications.

• The number of decimal places to be used with angle dimensions is presented.

• Changes under "limits of size" Rule #1:

Variations in size, referred to as "the actual size of an individual feature" are now referred to as "the actual local size of an individual feature" at each cross section.

In numerous places where the term size was used in the previous Standard, the terms actual local size, actual mating size, and actual mating envelope are substituted as appropriate for design intent and the expansion in distinguishing between the different uses of the term size.

• Regarding applicability of RFS and MMC in controlling straightness of an axis or center plane, the tolerance zone must contain the "derived median line" or the "derived median plane" rather than the "derived axis", "center line", or "derived center plane" of the previous Standard.

Changes under Rules #2 and #3:

Former Rules #2 and #3 regarding applicability of RFS, MMC, or LMC are replaced by a new Rule #2 that states that for all applicable geometric tolerances, "regardless of feature size" (RFS) applies with respect to the individual tolerance, datum reference, or both, where no modifying symbol is specified.

Maximum material condition (MMC) or least material condition (LMC) must be specified on the drawing where it is required.

Since the "regardless of feature size" condition is implied on all applicable geometric tolerancing for features of size, the RFS symbol is no longer necessary. This harmonizes U.S. practices with universal international (ISO) practices.

As an alternative interim practice (Rule 2a), RFS may be specified on the drawing as in the previous Standard.

The "symmetry" characteristic is reactivated and may be applied only on an RFS basis. Likewise, circular runout, total runout, and concentricity are reaffirmed as applicable only at RFS and cannot be modified to MMC or LMC.

Application and explanation of zero tolerance at least material condition (LMC) are added.

Virtual condition explanation is expanded and described as a constant value and as it relates to resultant condition as a worst case value. Inner boundary and outer boundary terms are also introduced as an associated method of identifying extreme limits of the concerned feature tolerances.

Resultant condition is introduced and explained as a worst case inner locus or outer locus condition.

Added figures to explain virtual condition boundary and resultant condition boundary as derived from the material condition specified at MMC or LMC.

"Datum features at virtual condition" explanation .s expanded to include the use of zero tolerance at MMC or LMC where a virtual condition equal to the maximum material condition is desired.

The "dimension origin" symbol and method are expanded for use with angular features.

The definition of radius is added.

A new "controlled radius" symbol replaces the symbol formerly used to specify a tangent radius without flats and reversals. The existing "radius" symbol is retained, but its meaning now permits flats and reversals in the surface contour.

• A standard method is added for identifying tolerances that apply using a statistical basis. The "statistical tolerance" symbol is introduced.

A5 SECTION 3, SYMBOLOGY

• The universal (ISO) datum feature symbol is adopted and replaces the previous one. Construction and application of the datum feature symbol and its use when establishing datums are added. The datum feature symbol is applied to the concerned feature surface outline, extension line, dimension line, feature control frame, dimension leader line, etc., in keeping with the principles established and the options provided.

• Explanation is added for placement of a datum target area size outside the datum target symbol when there is insufficient space within the symbol's upper compartment.

• Use of the material condition symbol for RFS is no longer necessary. The "regardless of feature size" condition applies where the symbols for MMC or LMC are not stated on size features.

• New symbols introduced and explained:

controlled radius statistical tolerance between free state tangent plane

• The "symmetry" characteristic and symbol are reactivated from earlier standards.

• The "all around" symbol explanation is added to the text.

• The "projected tolerance zone" symbol is now placed in the feature control frame, following the stated tolerance and any modifier. The dimension indicating the minimum height of the tolerance zone is also placed in the feature control frame, following the "projected tolerance zone" symbol.

A6 SECTION 4, DATUM REFERENCING

• The introductory paragraphs have been reorganized and rewritten to expand and clarify the prin ciples of identifying features of a part as datum features.

All illustrations have been revised to show the universal ISO datum feature symbol and remove the RFS material condition symbol.

Immobilization of the part relative to three mutually perpendicular planes in the datum reference frame is discussed and application relative to the "true geometric counterpart" is expanded.

A true geometric counterpart of a feature is further explained and examples are provided.

Subparagraph titles have been added for clarity and organization of subject matter.

A mathematically defined surface, such as a compound curve or contoured surface, can be used as a datum feature relative to a datum reference frame.

The use of "parts with inclined datum features" is introduced and explained in establishing a datum reference frame.

More explicit terms are provided to describe and explain the datum of a cylindrical feature. The datum of a cylindrical surface is the axis of the true geometric counterpart of the datum feature (for example, the actual mating size or the virtual condition boundary).

Paragraphs describing and explaining datum features "not subject to size variations" and datum features "subject to size variation" are reorganized, explained, and clarified.

The role of the "simulated datum" is clarified. The term actual mating envelope is inserted where appropriate.

Text on primary, secondary, and tertiary datums for diameter or width features, and under RFS. MMC, or LMC conditions, is expanded and explained using the terms simulated datum, actual mating envelope, true geometric counterpart, virtual condition, and least material condition.

Expansion of an explanation for the establishment of a single datum plane from two or more coplanar features is included.

An explanation of the use of a pattern of features as a single datum reference is expanded and illustrated.

The "simultaneous requirements" principle, where two or more features, or patterns of features, are related to common datums in the same order of precedence, is expanded and illustrated. Clarified that this principle does not apply to the lower segments of composite feature control frames unless specific notation is added.

• Where datum targets or equalizing datums are used on more complex parts and the datum feature symbol cannot be conveniently tied to a specific feature, the datum feature symbol is not required. The datum reference frame will be established by the collective points, lines, areas, or portions of the surfaces involved.

• On equalizing datums. it is permissible to u*e the datum feature symbol to identify the equalized theoretical center planes of the datum reference frame established. This is an exception and should be done only when necessary and in conjunction with datum targets.

• For irregular or step datum surfaces, the datum plane should contain at least one of the datum targets.

• In expansion of the datum nomenclature, all appropriate figures were expanded or revised to include explanation of the relationships between the datum feature; simulated datum feature; simulated datum plane, axis, or center plane: datum feature simulator; true geometric counterpart; and datum plane, axis, or center plane.

• Numerous figures were expanded to provide more information.

• New figures were added for "Inclined Datum Features", "Orientation of Two Datum Planes Through a Hole", "Secondary and Tertiary Datum Features at LMC". "Hole Pattern Identified as Datum", "Simultaneous Position and Profile Tolerances". "Datum Targets Used to Establish Datum Reference Frame for Complex Part", and 'Two Datum Features, Single Datum Axis."

A7 SECTION 5, TOLERANCES OF LOCATION

• Subparagraph headings are added to identify subject matter more clearly.

• The universal ISO datum feature symbol is inserted in all illustrations replacing the previous datum feature symbol.

• The terms actual mating size and actual mating envelope are substituted for actual size wherever appropriate throughout the section.

A note is added to acknowledge that the axis and surface explanations for positional tolerance at MMC do not always yield equivalent results. In such cases, the surface interpretation shall take precedence.

The explanation of "multiple patterns of features located by basic dimensions relative to common datums" is expanded and explained.

The differences in meaning between "common datum features not subject to size tolerances or size features specified on an RFS basis" and "patterns of features specified on an MMC basis" is explained.

A number of new illustrations arc added to expand the explanation of composite positional tolerancing.

The composite positional tolerancing text is revised, expanded, and rewritten.

The relationship of the Pattern-Locating Tolerance Zone Framework {PLTZF) and the Feature-Relating Tolerance Zone Framework (FRTZF) is expanded and explained in new text and numerous illustrations.

The PLTZF is located by basic dimensions from specified datums and the datum reference frame. It specifies the larger positional tolerance for the location of the pattern of features as a group.

The FRTZF governs the smaller positional tolerance for each feature within the pattern (feature-to-feature relationship). Basic dimensions that locate the PLTZF from datums are not applicable to the FRTZF.

Where datum references are not specified in the lower segment of a composite feature control frame, the FRTZF is free to be located and oriented (shift and/or tilt) within the boundaries established and governed by the PLTZF.

If datums are specified in the lower segment of the composite feature control frame, they govern the orientation only of the FRTZF to the specified datums and relative to the PLTZF.

Where datum references are specified in the lower segment of the composite feature control frame, one or more of the datums specified in the upper segment of the composite frame are repeated, as applicable and in the same order of precedence as the PLTZF. to govern the orientation of the FRTZF.

• If different datum references, different datum modifiers, or the same datums in a different order of precedence are contemplated as upper and lower segments of a composite feature control frame, this constitutes a different datum reference frame and is not to be specified using the composite tolerance method. In such cases, separately specified s.ngle-segment feature control frames are used, each including applicable datums. Each single segment is an independent separate requirement.

• Explanation of the use of two single-segment feature control frames is expanded to denote (or specify) design requirements for independent basic-dimension-related verifications.

• "Radial hole pattern located by composite tolerancing" illustrations are shown using a more common application where the primary datum is a plane feature rather than a size feature.

• Text and illustrations are added where the composite tolerancing principle is extended to addition of a secondary datum in the lower segment of the feature control frame.

• Distinction is made between use of composite positional tolerancing with primary and secondary datums in the lower segment in an "orientation only" requirement versus use of two single-segment feature control frames to depict separale independent design requirements.

• The use of the "projected tolerance zone" symbol within the feature control frame, following the geometrical tolerance and any material condition symbol, is presented.

• To invoke the boundary positional tolerarcing concept as a requirement on an elongated or irregular feature of size, the term BOUNDARY is placed beneath the feature control frame.

• Clarification and expansion of "Positional Tolerancing for Coaxial Holes of Same Size" and for different size, using composite positional tolerancing are provided.

• The definition of concentricity is revised and refined.

• A distinction is made between runout (RFS) as a control for elements of a surface of revolution; positional tolerance. either MMC or RFS, to de-

•vermine the axis of the actual mating envelope; and concentricity, requiring the establishment and verification of the feature's median points and median line. Illustrations were either revised or added :o explain these principles.

• The "symmetry" characteristic and symbol are reactivated from previous standards.

• A distinction is made between positional tolerance for symmetrical relationships, either MMC Dr RFS, to determine the center plane of the actual mating envelope; and symmetry, requiring establishment and verification of the feature's median points. Illustrations were either revised or added to explain these principles.

• The "spherical diameter" symbol is introduced as used in the feature control frame to indicate a spherical diameter tolerance zone.

A8 SECTION 6, TOLERANCES OF FORM, PROFILE, ORIENTATION, AND RUNOUT

• Subparagraphs are given titles for clarity and organization of subject matter.

• The universal ISO datum feature symbol is inserted to replace all former datum feature symbols in illustrations.

• The option is added, where appropriate, to use profile tolerancing for location of features.

• Coverage is added to emphasize the necessity to identify datum features on a part from which dimensions controlling orientation, runout, and where necessary, profile are related.

• The term derived median line replaces axis in the definition of a straightness tolerance.

• A straightness tolerance on a feature of size, normally permitting a violation of the MMC boundary, is not allowed when used in conjunction with an orientation or position tolerance. In such a case, the specified straightness tolerance value shall not be greater than the specified orientation or position tolerance values.

• The term actual local size is inserted where appropriate.

• Where function requires straight line elements to be related to a datum feature, profile of a line, related to datums, should be specified.

• The requirements imposed by circularity tolerancing are relaxed and applicability broadened

• Explanation and illustration are added for combining profile tolerancing with positional tolerancing to control the boundary of a noncylindrical feature. To invoke this control, the term BOUNDARY is placed beneath the positional tolerance feature control frame.

• Composite profile tolerance explanation, application, methodology, and illustrations are added.

• The "tangent plane" concept and symbol are introduced, explained, and illustrated.

• Angularity tolerance using a cylindrical tolerance zone is added.

• Angularity tolerance using a tolerance zone defined by two parallel lines is added.

• Parallelism tolerance zone coverage is expanded to include a center plane relative to the datum plane.

• On specifying straightness at RFS or MMC, the term derived median line of the feature actual local sizes replaces derived axis or center line of the actual feature.

• An example is added for profile bilateral tolerance with unequal distribution.

• The "between" symbol is illustrated.

• An example is added for "profile of a surface for coplanar surfaces to a datum established by two surfaces."

• "Composite profile tolerancing of an irregular surface" and "composite profile of a surface" examples are added.

• The "free state" symbol is introduced and explained. It is to be used instead of the previous equivalent note.

A9 APPENDIX Ar PRINCIPAL CHANGES AND IMPROVEMENTS

• A new Appendix A is added to provide a list of changes, additions, extensions of principles, and resolutions of differences found in this revision compared to the previous issue, ANSI Y14.5M-1982.

• In the 1982 issue, Appendix A was titled "Dimensioning for Computer-Aided Design and Com-

putcr-Aided Manufacturing Mode." It provided guidelines applicable to the newly evolving CAD/ CAM mode of preparing engineering drawings. Now, with interactive computer graphics systems more fully matured, national and international acceptance has been achieved. Correspondingly, this has resulted in recognition that the ASME Y14 series standards are the appropriate source for providing the definition of products, regardless of whether a computer or noncomputer (manual) method is used. Thus, special CAD/CAM explanation is reduced to very basic coverage within *Jie body of the Standard.

A10 APPENDIX B, FORMULAS FOR POSITIONAL TOLERANCING

• Additional formula symbols are added:

D = minimum depth of thread or minimum thickness of part with restrained or fixed fastener P = maximum thickness of part with clearance hole, or maximum projection of fastener, such as a stud

• In the fixed fastener case, clarification is made that 'the same positional tolerance in each of the parts to be assembled" applies when the formulas under para. B4 are used. Also clarified is the point that the total positional tolerances of both holes (27*) can be separated into 71, and T2 in any appropriate manner such that 2T = T} + T2.

• New coverage and formulas replace and are added giving "provision for out-of-squareness when projected tolerance zone is not used" on features such as threaded holes or dowel holes.

A11 APPENDIX C, FORM, PROPORTION, AND COMPARISON OF SYMBOLS

• The explanatory text is reworded and condensed for clarity.

• The universal ISO datum feature symbol replaces the former one. The "symmetry" symbol is reinstated and the "regardless of feature size" (RFS) symbol is removed.

• New symbols introduced:

tangent plane free state controlled radius between statistical tolerance

• Symbols added under the ISO column in the Comparison of Symbols chart:

all around (proposed) least material condition tangent plane (proposed) free state dimension origin arc length spherical radius spherical diameter

A12 APPENDIX D, FORMER PRACTICES

• Information on significant former practices once featured in the 1982 issue of this Standard is provided along with related illustrations.

A13 APPENDIX E, DECISION DIAGRAMS FOR GEOMETRIC CONTROL

• A new appendix is added to assist in the selection of proper geometric tolerancing controls and application. The diagram display will aid in the understanding of the coordinated flow of the geometric dimensioning and tolerancing system.

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Responses

  • Melody
    Where to find true geometric counterpart for a mathematically defined surface?
    7 years ago
  • nora
    How does one derive the tolerance value in the FRTZF?
    1 year ago
  • David
    What is the definition of an actual mating envelope in geometric dimensioning an toleranceing?
    10 months ago
  • Blanco
    CAN frtzf BE LARGER THAN pltzf?
    5 months ago
  • leah
    Where no geomtric tolerance are specified, the worstcase boundary of a hole is referred to?
    10 days ago

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