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Training Course Contents
This goal of this course to help you understand and interpret the fundamentals of GD&T. It is based on the ASME Y14.5 – 2009 standard. Formally the ASME Y14.5M – 1994 standard.
By definition, GD&T establishes uniform practices for stating and interpreting dimensions, tolerancing, and related requirements for use on engineering drawings and in related documents.
Course Info at a glance
In-class 2 day course (6 hours/day)
Or Online 2 days (5 hours/day)
Why take this course
GD&T is essential to ensure functional information and design intent from the assembly to its individual parts. This insures accurate fitting assemblies and spare parts regardless of where they are manufactured.
Designers, toolmakers, inspectors and project managers will greatly benefit from GD&T knowledge.
What the course covers
Our Geometric Dimensioning and Tolerancing course covers the fundamentals and principles of the ASME Y14.5 2009 GD&T standard. The course focuses on the geometric characteristic symbols explaining in detail each symbol, feature control frames, different modifiers and how they affect tolerancing when placed in the feature control frame.
The course also goes into depth on datums and datum reference frames, partial datums and datum target points. You will be exposed to methods of inspection for the characteristics symbols, composite feature control frames and design exercises. The course is delivered with a combination of principles, exercises and drawing examples from an instructor with professional ASME standing and over 20 years of practical experience.
Requirements & Benefits
Basic understanding of mechanical engineering and drawings
No SOLIDWORKS experience required
Able to take two days out for training
Geometric Characteristic Symbols
Feature Control Frames
Datum Frames, Targets & Partial Datums
Skills you will acquire
Able to understand and apply GD&T
Different methods of inspection
An understanding of the ASME Y14.5 – 2009 standard
GD&T Fundamentals Overview & Lessons
The following lessons are included in the course
- Identify the benefits of Geometric Dimensioning and Tolerancing.
- Identify the geometric characteristic symbols used in GD&T and understand their meaning.
- Interpret feature control frames and apply them on drawings.
- Interpret and apply modifiers in feature control frames and how they affect the geometric tolerance specified.
- Interpret Datum Reference Frames illustrating primary, secondary, and tertiary datums.
- Understand the function of datum targets and partial datums.
- Discuss methods of inspection for the different geometric characteristic symbols.
- Recognize composite feature control frames and illustrate how to interpret them on drawings.
- Interpret different examples of GD&T applications from various drawing examples.
Lesson 1: Introduction
- Benefits of Geometric Dimensioning & Tolerancing
- Co-ordinate Tolerancing Vs Diametrical Tolerancing
- Types of Dimensions
Lesson 2: Characteristic Symbols
- Characteristics Symbols
- ASME Y145 – 2009
- Geometric Characteristics and their tolerance zones
- Form Tolerances
- Straightness (of a flat surface)
- Straightness (of an axis)
- Circularity or Roundness
- Profile tolerances
- Profile of a line
- Profile of a surface
- Orientation tolerances
- Location tolerances
- Runout tolerances
- Circular runout
- Total runout
Lesson 3: Feature Control Frames
- Feature Control Frame Breakdown
- Placement of Feature Control Frames on Drawings
- Feature Control Frame Exercise
- Placement of Datums
- Placement of Datums ASME Y145 – 2009 & Y145M – 1994 vs ANSI Y145M – 198236
- Qualifying Datums vs Designated Datums
- Feature Control Frame Exercise #2
- Placing Feature Control Frames on drawings Exercise
Lesson 4: Modifiers
- Maximum Material Condition MMC
- Virtual Condition
- Positional Callout illustrating the effects of MMC
- Straightness Callout illustrating the effects of MMC
- Positional tolerance of a slot in MMC
- Bi-directional Positional Tolerance in MMC
- Simultaneous Requirement
- Interpreting Positional Diametrical Tolerance Zone in MMC
- Least Material Condition (LMC)
- Virtual Condition
- Least Material Condition Exercise
- Regardless of Feature Size (RFS)
- Complete list of modifying symbols
- Projected Tolerance Zone
- Established Rules
- Review Exercise
Lesson 5: Inspection Methods
- Straightness of a Flat Surface
- Straightness of an Axis (Relatively Round)
- Straightness of an Axis MMC
- Circularity or Roundness of a Cylinder
- Cylindricity of a Cylinder
- Inspection Methods Exercise (Form Tolerances)
- Perpendicularity of a Surface
- Perpendicularity of a Cylindrical Feature in MMC
- Angularity of a Surface
- Parallelism of a Surface
- Parallelism of a Cylindrical Feature at RFS
- Inspection Methods Exercise (Orientation Tolerances)
- Profile of a Line
- Profile of a Surface
- Profile of a Surface vs Parallelism
- Additional Considerations with Profile Tolerance
- Circular Runout
- Total Runout
- Runout – Circular for Squareness
- Symmetry (non round features)
- Inspection Methods Exercise – Summary
Lesson 6: Datums
- Datum Referencing
- Partial Datums
- Datum Targets
- Datum Reference in a MMB or LMB Condition
- Datum Exercise
Lesson 7: Positional Charts
- Diametrical tolerance VS plus / minus tolerance
- Radial Positional Chart Exercise 1
- Radial Positional Chart Exercise 2
Lesson 8: Composite Feature Control Frames
- Exercise 1
- Exercise 2
- Exercise 3
- Exercise 4
- Exercise 5
- Exercise 6
“As a new topic to me it was very easy to pick up and remember. The GD&T Fundamentals course helped me to understand the true function of the part and its relationship to mating surfaces. The instructor was able to carry the course at an excellent speed leaving students enough time to grasp the concept.”
— Steven Cargnello, Marsh Brothers Aviation.
“Presented the material in a manner that was east to absorb.”
— Paul Bolduc, Bend-All.
“Well organized course, taking it step-by-step. The instructor answered the questions completely and was able to keep the course interesting despite the tough subject.”
— Kevin Lowry, TMI.
“The instructor was very knowledgeable and clearly passionate about the subject matter. This will help greatly with checking our purchased parts.”
— Alexandre Giles, Multimatic Manufacturing.
“Enthusiastic instructor. Small class, solid training manual. Need GD&T to do my GR&R Studies. Oh and an A+ Coffee Machine!”
— Peter Ngyen, Multimatic Manufacturing.
“My overall knowledge of GD&T has vastly improved. I will be able to look at drawings and fully understand them.”
— Jonathan Koot, Exco Engineering.
“Small class made for a pretty thorough learning experience. Very knowledgeable and personable instructor.”
— Graham Jokic, XL Tool.
“Very good instructor with expert knowledge, and was able to answer all the questions I had. Good discussions with real world examples. The small class size provides the opportunity for question and answers sessions.”
— Warner Wong, L3-Wescam.
“The instructor was from the same background as myself and used examples representative of what is done throughout our workplace. He was confident, comfortable and knew his material. I will be able to create improved prints that indicate/ instruct what is required will reduce re-work and scrapped parts. More accurate and complete prints should reduce assumptions made by the machinists.”
— Chris Lishman, Armo-Tool Ltd.
“I liked how GD&T works, and it has very practical applications to communicate fit form and function on drawings. I hope to see this used more at my work to cut down on the hand-written notes we currently use, and aid in our shop floor understanding of what the engineers were thinking as they created the parts.”
— Travis Boyd, Armo-Tool Ltd.
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Geometric dimensioning and tolerancing
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Example of geometric dimensioning and tolerancing
Geometric dimensioning and tolerancing (GD&T) is a system for defining and communicating engineering tolerances . It uses a symbolic language on engineering drawings and computer-generated three-dimensional solid models that explicitly describe nominal geometry and its allowable variation. It tells the manufacturing staff and machines what degree of accuracy and precision is needed on each controlled feature of the part. GD&T is used to define the nominal (theoretically perfect) geometry of parts and assemblies, to define the allowable variation in form and possible size of individual features, and to define the allowable variation between features.
- Dimensioning specifications define the nominal, as-modeled or as-intended geometry. One example is a basic dimension.
- Tolerancing specifications define the allowable variation for the form and possibly the size of individual features, and the allowable variation in orientation and location between features. Two examples are linear dimensions and feature control frames using a datum reference (both shown above).
There are several standards available worldwide that describe the symbols and define the rules used in GD&T. One such standard is American Society of Mechanical Engineers (ASME) Y14.5-2009. This article is based on that standard, but other standards, such as those from the International Organization for Standardization (ISO), may vary slightly. The Y14.5 standard has the advantage of providing a fairly complete set of standards for GD&T in one document. The ISO standards, in comparison, typically only address a single topic at a time. There are separate standards that provide the details for each of the major symbols and topics below (e.g. position, flatness, profile, etc.).
- 1 Origin
- 2 Dimensioning and tolerancing philosophy
- 3 Symbols
- 3.1 Datums and datum references
- 4 Data exchange
- 5 Documents and standards
- 5.1 ISO TC 10 Technical product documentation
- 5.2 ISO/TC 213 Dimensional and geometrical product specifications and verification
- 5.3 ASME standards
- 5.4 GD&T standards for data exchange and integration
- 6 See also
- 7 References
- 8 Further reading
- 9 External links
Origin[ edit ]
The origin of GD&T is credited to Stanley Parker , who developed the concept of “true position”. While little is known about Parker’s life, it is known that he worked at the Royal Torpedo Factory in Alexandria, West Dunbartonshire , Scotland . His work increased production of naval weapons by new contractors.
In 1940, Parker published Notes on Design and Inspection of Mass Production Engineering Work, the earliest work on geometric dimensioning and tolerancing.  In 1956, Parker published Drawings and Dimensions, which became the basic reference in the field. 
Dimensioning and tolerancing philosophy[ edit ]
According to the ASME Y14.5-2009  standard, the purpose of geometric dimensioning and tolerancing (GD&T) is to describe the engineering intent of parts and assemblies. The datum reference frame can describe how the part fits or functions. GD&T can more accurately define the dimensional requirements for a part, allowing over 50% more tolerance zone than coordinate (or linear) dimensioning in some cases. Proper application of GD&T will ensure that the part defined on the drawing has the desired form, fit (within limits) and function with the largest possible tolerances. GD&T can add quality and reduce cost at the same time through producibility.
There are some fundamental rules that need to be applied (these can be found on page 7 of the 2009 edition of the standard):
- All dimensions must have a tolerance. Every feature on every manufactured part is subject to variation, therefore, the limits of allowable variation must be specified. Plus and minus tolerances may be applied directly to dimensions or applied from a general tolerance block or general note. For basic dimensions, geometric tolerances are indirectly applied in a related Feature Control Frame. The only exceptions are for dimensions marked as minimum, maximum, stock or reference.
- Dimensions define the nominal geometry and allowable variation. Measurement and scaling of the drawing is not allowed except in certain cases.
- Engineering drawings define the requirements of finished (complete) parts. Every dimension and tolerance required to define the finished part shall be shown on the drawing. If additional dimensions would be helpful, but are not required, they may be marked as reference.
- Dimensions should be applied to features and arranged in such a way as to represent the function of the features. Additionally, dimensions should not be subject to more than one interpretation.
- Descriptions of manufacturing methods should be avoided. The geometry should be described without explicitly defining the method of manufacture.
- If certain sizes are required during manufacturing but are not required in the final geometry (due to shrinkage or other causes) they should be marked as non-mandatory.
- All dimensioning and tolerancing should be arranged for maximum readability and should be applied to visible lines in true profiles.
- When geometry is normally controlled by gage sizes or by code (e.g. stock materials), the dimension(s) shall be included with the gage or code number in parentheses following or below the dimension.
- Angles of 90° are assumed when lines (including center lines) are shown at right angles, but no angular dimension is explicitly shown. (This also applies to other orthogonal angles of 0°, 180°, 270°, etc.)
- Dimensions and tolerances are valid at 20 °C / 101.3 kPa unless stated otherwise.
- Unless explicitly stated, all dimensions and tolerances are only valid when the item is in a free state.
- Dimensions and tolerances apply to the length, width, and depth of a feature including form variation.
- Dimensions and tolerances only apply at the level of the drawing where they are specified. It is not mandatory that they apply at other drawing levels, unless the specifications are repeated on the higher level drawing(s).
(Note: The rules above are not the exact rules stated in the ASME Y14.5-2009 standard.)
Symbols[ edit ]
Tolerances: Type of tolerances used with symbols in feature control frames can be 1) equal bilateral 2) unequal bilateral 3) unilateral 4) no particular distribution (a “floating” zone)
Tolerances for the profile symbols are equal bilateral unless otherwise specified, and for the position symbol tolerances are always equal bilateral. For example, the position of a hole has a tolerance of .020 inches. This means the hole can move +/- .010 inches, which is an equal bilateral tolerance. It does not mean the hole can move +.015/-.005 inches, which is an unequal bilateral tolerance. Unequal bilateral and unilateral tolerances for profile are specified by adding further information to clearly show this is what is required.
|Type of control||Geometric characteristics||Symbol||Character|
( Unicode )
|Can be applied to a surface?||Can be applied to a feature of size?||Can affect virtual condition?||Datum reference used?||Can use||Can use||Can be affected by a bonus tolerance?||Can be affected by a shift tolerance?|
|Profile||Profile of a line|
|Profile||Profile of a surface|
- When applied to a feature-of-size.
- Can also be used as a form control without a datum reference.
- When a datum feature-of-size is referenced with the MMC modifier.
- When an MMC modifier is used.
- Automatic per rule #3.
- The symmetry symbol’s characteristics were not included in the version of the chart that this chart is derived from. The symmetry symbol was dropped from the Y14.5M standard around 1982 and re-added around 1994.
( Unicode )
|Free state||Applies only when part is otherwise restrained|
|Least material condition (LMC)||Useful to maintain minimum wall thickness|
|Maximum material condition (MMC)||Provides bonus tolerance only for a feature of size|
|Projected tolerance zone||Useful on threaded holes for long studs|
|Regardless of feature size (RFS)||Not part of the 1994 version. See para. A5, bullet 3. Also para. D3. Also, Figure 3-8.|
|Tangent plane||Useful for interfaces where form is not required|
|Continuous Feature||Identifies a group of features that should be treated geometrically as a single feature|
|Statistical Tolerance||Appears in the 1994 version of the standard, assumes appropriate statistical process control.|
|Unequal Bilateral||Appears in the 2009 version of the standard, and refers to unequal profile distribution.|
Datums and datum references[ edit ]
A datum is a virtual ideal plane, line, point, or axis. A datum feature is a physical feature of a part identified by a datum feature symbol and corresponding datum feature triangle, e.g.,
These are then referred to by one or more ‘datum references’ which indicate measurements that should be made with respect to the corresponding datum feature .
Data exchange[ edit ]
Exchange of geometric dimensioning and tolerancing (GD&T) information between CAD systems is available on different levels of fidelity for different purposes:
- In the early days of CAD, exchange-only lines, texts and symbols were written into the exchange file. A receiving system could display them on the screen or print them out, but only a human could interpret them.
- GD&T presentation: On a next higher level the presentation information is enhanced by grouping them together into callouts for a particular purpose, e.g. a datum feature callout and a datum reference frame. And there is also the information which of the curves in the file are leader, projection or dimension curves and which are used to form the shape of a product.
- GD&T representation: Unlike GD&T presentation, the GD&T representation does not deal with how the information is presented to the user but only deals with which element of a shape of a product has which GD&T characteristic. A system supporting GD&T representation may display GD&T information in some tree and other dialogs and allow the user to directly select and highlight the corresponding feature on the shape of the product, 2D and 3D.
- Ideally both GD&T presentation and representation are available in the exchange file and are associated with each other. Then a receiving system can allow a user to select a GD&T callout and get the corresponding feature highlighted on the shape of the product.
- An enhancement of GD&T representation is defining a formal language for GD&T (similar to a programming language) which also has built-in rules and restrictions for the proper GD&T usage. This is still a research area (see below reference to McCaleb and ISO 10303-1666).
- GD&T validation: Based on GD&T representation data (but not on GD&T presentation) and the shape of a product in some useful format (e.g. a boundary representation ), it is possible to validate the completeness and consistency of the GD&T information. The software tool FBTol from the Kansas City Plant is probably the first one in this area.
- GD&T representation information can also be used for the software assisted manufacturing planning and cost calculation of parts. See ISO 10303-224 and 238 below.
Documents and standards[ edit ]
ISO TC 10 Technical product documentation[ edit ]
- ISO 128 Technical drawings – Indication of dimensions and tolerances
- ISO 7083 Symbols for geometrical tolerancing – Proportions and dimensions
- ISO 13715 Technical drawings – Edges of undefined shape – Vocabulary and indications
- ISO 15786 Simplified representation and dimensioning of holes
- ISO 16792:2015 Technical product documentation—Digital product definition data practices (Note: ISO 16792:2006 was derived from ASME Y14.41-2003 by permission of ASME)
ISO/TC 213 Dimensional and geometrical product specifications and verification[ edit ]
In ISO/TR 14638 GPS – Masterplan the distinction between fundamental, global, general and complementary GPS standards is made.
- Fundamental GPS standards
- ISO 8015 Concepts, principles and rules
- Global GPS standards
- ISO 14660-1 Geometrical features
- ISO/TS 17, orientation and location
- ISO 1101 Geometrical tolerancing – Tolerances of form, orientation, location and run-out
- Amendment 1 Representation of specifications in the form of a 3D model
- ISO 1119 Series of conical tapers and taper angles
- ISO 2692 Geometrical tolerancing – Maximum material requirement (MMR), least material requirement (LMR) and reciprocity requirement (RPR)
- ISO 3040 Dimensioning and tolerancing – Cones
- ISO 5458 Geometrical tolerancing – Positional tolerancing
- ISO 5459 Geometrical tolerancing – Datums and datum systems
- ISO 10578 Tolerancing of orientation and location – Projected tolerance zone
- ISO 10579 Dimensioning and tolerancing – Non-rigid parts
- ISO 14406 Extraction
- ISO 22432 Features used in specification and verification
- General GPS standards: Areal and profile surface texture
- ISO 1302 Indication of surface texture in technical product documentation
- ISO 3274 Surface texture: Profile method – Nominal characteristics of contact (stylus) instruments
- ISO 4287 Surface texture: Profile method – Terms, definitions and surface texture parameters
- ISO 4288 Surface texture: Profile method – Rules and procedures for the assessment of surface texture
- ISO 8785 Surface imperfections – Terms, definitions and parameters
- Form of a surface independent of a datum or datum system. Each of them has a part 1 for the Vocabulary and parameters and a part 2 for the Specification operators:
- ISO 12180 Cylindricity
- ISO 12181 Roundness
- ISO 12780 Straightness
- ISO 12781 Flatness
- ISO 25178 Surface texture: Areal
- General GPS standards: Extraction and filtration techniques
- ISO/TS 1661 Filtration
- ISO 11562 Surface texture: Profile method – Metrological characteristics of phase correct filters
- ISO 12085 Surface texture: Profile method – Motif parameters
- ISO 13565 Profile method; Surfaces having stratified functional properties
ASME standards[ edit ]
- ASME Y14.41-2009 Digital Product Definition Data Practices
- ASME Y14.5 – Dimensioning and Tolerancing
- ASME Y14.5M-1994 Dimensioning and Tolerancing
- ASME Y14.5.1M-1994 Mathematical Definition of Dimensioning and Tolerancing Principles
ASME is also working on a Spanish translation for the ASME Y14.5 – Dimensioning and Tolerancing Standard.
GD&T standards for data exchange and integration[ edit ]
- ISO 10303 Industrial automation systems and integration — Product data representation and exchange
- ISO 10303-47 Integrated generic resource: Shape variation tolerances
- ISO/TS 10303-1130 Application module: Derived shape element
- ISO/TS 10303-1050 Application module: Dimension tolerance
- ISO/TS 10303-1051 Application module: Geometric tolerance
- ISO/TS 10303-1052 Application module: Default tolerance
- ISO/TS 10303-1666 Application module: Extended geometric tolerance
- ISO 10303-203 Application protocol: Configuration controlled 3D design of mechanical parts and assemblies
- ISO 10303-210 Application protocol: Electronic assembly, interconnection, and packaging design
- ISO 10303-214 Application protocol: Core data for automotive mechanical design processes
- ISO 10303-224 Application protocol: Mechanical product definition for process planning using machining features
- ISO 10303-238 Application protocol: Application interpreted model for computerized numerical controllers (STEP-NC)
See also[ edit ]
- Specification of surface finish
- Engineering fit
- Engineering tolerance
References[ edit ]
This article includes a list of references , but its sources remain unclear because it has insufficient inline citations . Please help to improve this article by introducing more precise citations. (April 2010) ( Learn how and when to remove this template message )
- ^ a b MacMillan, David M.; Krandall, Rollande (2014). “Bibliography for Dimensioning and Tolerancing” . Circuitous Root. Retrieved October 24, 2018.
- ^ Dimensioning and Tolerancing, ASME y14.5-2009. NY: American Society of Mechanical Engineers. 2009. ISBN 0-7918-3192-2 .
Further reading[ edit ]
- McCale, Michael R. (1999). “A Conceptual Data Model of Datum Systems” (PDF). Journal of Research of the National Institute of Standards and Technology. 104 (4): 349–400. doi : 10.6028/jres.104.024 .
- Henzold, Georg (2006). Geometrical Dimensioning and Tolerancing for Design, Manufacturing and Inspection (2nd ed.). Oxford, UK: Elsevier. ISBN 978-0750667388 .
- Srinivasan, Vijay (2008). “Standardizing the specification, verification, and exchange of product geometry: Research, status and trends”. Computer-Aided Design. 40 (7): 738–49. doi : 10.1016/j.cad.2007.06.006 .
- Drake, Jr., Paul J. (1999). Dimensioning and Tolerancing Handbook. New York: McGraw-Hill. ISBN 978-0070181311 .
- Neumann, Scott; Neumann, Al (2009). GeoTol Pro: A Practical Guide to Geometric Tolerancing per ASME Y14.5-2009. Dearborn, MI: Society of Manufacturing Engineers. ISBN 978-0-87263-865-5 .
- Bramble, Kelly L. (2009). Geometric Boundaries II, Practical Guide to Interpretation and Application ASME Y14.5-2009,. Engineers Edge.
- Wilson, Bruce A. (2005). Design Dimensioning and Tolerancing. US: Goodheart-Wilcox. p. 275. ISBN 978-1-59070-328-1 .
External links[ edit ]
|Wikimedia Commons has media related to Geometric dimensioning and tolerancing .|
- General tolerances for linear and angular dimensions according to ISO 2768
- Interactive map of GD&T
- What is GD&T
- The importance of GD&T
- GD&T Glossary of Terms and Definitions
- GDT: Introduction
- ASME Certification
- Changes and Additions to ASME Y14.5M
- NIST MBE PMI Validation and Conformance Testing Project Tests implementations of GD&T in CAD software
- STEP File Analyzer and Viewer – Analyze GD&T in a STEP file
- Technical drawing
- Articles lacking in-text citations from April 2010
- All articles lacking in-text citations
- Commons category link is on Wikidata
- This page was last edited on 6 November 2018, at 17:56 (UTC).
- Text is available under the Creative Commons Attribution-ShareAlike License ;
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