GdT _Theory_1st Principle_ Training Manual LEVEL 1

Geometric Dimensioning & Tolerancing (GD & T) Level 1 Training Manual

INDEX Chapter 1. Course Introduction ……………………………………….. Introduction Hexagon quality assurance documentation Agenda Course objectives 2. Introduction to Geometrical Product Specifications……………… Introduction to GPS Requirements of GPS 3. Datums…………………………………………………… Datum’s Reference frames Axis Plane Target 4. Form Tolerances……………………………………………… Circularity(Roundness) Straightness Flatness Cylindricity 5. Location Tolerances…………………………………………… Location Regardless of Feature size Maximum Material Condition (Maximum Material Reference) Concentricity/Coaxiality Symmetry 6. Orientation Tolerances………………………………………………………. Parallelism Perpendicularity Angularity 7. Profile Tolerances…………………………………………. Profile of a line Profile of a surface 8. Runout Tolerances………………………………………….. Runout Circular Runout Total Runout 9. Appendix………………………………………….. Further MMC options Basic Symbols Hexagon contacts

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© Hexagon Metrology GD & T – Issue 1 – May2006

Course Introduction

IN THIS CHAPTER

· · · ·

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Introduction Hexagon quality assurance documentation Agenda Course objectives


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Introduction to GD & T Training Course Welcome to Hexagon Metrology Hexagon metrology welcomes you today to their metrology facility and hopes that your visit will be enjoyable, interesting and informative. During the introduction session we respectively request that you take note of any health and safety requirements and that you complete the Hexagon Metrology quality assurance documentation. The information provided will contribute to future development of both existing and new training courses.

Introduction Overview · Welcome · Introduction to Hexagon Metrology · Health & Safety · Course subsistence arrangements · Course Content and Times · Trainee registration and background · Training manual contents · Workbook principals · Evaluation · Certification · Further courses

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Course Agenda Please see the following overview of the course agenda for both the Day 1 Ø Ø

Introduction/Course aims & Objectives GD & T Theory o Introduction to Geometric Product Specifications (GPS) o Overview of Geometric Dimensioning and Tolerancing (GD & T) o Standards o Datum Systems o Understanding the Basic Symbols of GD & T o Form o Location o Orientation o Runout o Profile o Maximum Material Condition

Please note: Course content and order is subject to change at the discretion of the Training Instructor

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Course Objectives To achieve a Basic understanding of Geometric Dimensioning and Tolerancing (GD & T) in the following areas: · · · · · ·

Introduction to Geometric Product Specifications (GPS) Overview of Geometric Dimensioning and Tolerancing (GD & T) Standards Datum Systems Understanding the Basic Symbols of GD & T Maximum Material Condition

Training Manual and workbook Each trainee will be provided with a training manual and workbook covering different aspects of the level 1 course only What this training manual is! The training manual is provided as a reminder to each student of the important requirements that lead to the successful understanding of GD & T principles and appropriate measurement strategies. What this training manual is not! It is not another version of a technical manual. or standard What is the workbook? The workbook provides evidence of competence achieved by each trainee during the training course. It will include exercises to check that learning has taken place Evaluation As we all know evaluation is very important. The workbook will provide a method of evaluating each trainee’s competence and give the trainee evidence to take back for themselves and their employer of their achievements during the course. Based on the results obtained and evaluated by your training instructor, a certificate will be issued. The assessment of competence can only be judged at the time of the course. This does not mean that the trainee can be classed as an expert, it is important for the trainees to implement the techniques they have learned on their return to their respective company. Course evaluation Hexagon metrology takes pride in the services it provides and continues to strive to improve this quality service. It is important for us to get feedback about our services. As part of this process, we will kindly request that on completion of your course you complete a training evaluation form. During each session of the course the students will be encouraged to participate in both the theoretical and practical elements. Questions and answers sessions for the above elements and any other requirements will be included as requested. 6


Geometrical Product Specification (GPS) IN THIS CHAPTER Ø Ø

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Introduction to GPS Requirements of GPS


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At the first design stages of component parts, the designer imagines the product to be an ideal, perfect object. All component parts are assumed to be of perfect form and size. During the manufacturing processes component parts vary in many different ways, form errors and changes to the surface parameters become apparent when using different manufacturing methods. These errors and parameter changes can have a great effect on the functionality of the component. It is therefore critical that these definitions are standardised and understood, so that the variation that is inherent to manufacturing processes can be taken into account to minimise waste products and assemblies. To be able understand the geometrical variations within component parts a set of requirements have been produced. These are known as Geometrical Product Specifications (GPS), covering requirements on sizes and dimensions, geometrical tolerances and geometrical properties of surface Form of line and surface Ø Independent of datum Ø Dependent on datum

Ø Ø Ø Ø

Size Distance Radius Angle

GPS Model

Ø Ø Ø Ø

Ø

Orientation

Ø

Location

Ø

Circular runout

Ø

Total runout

Ø

Datum

Roughness profile Waviness profile Primary profile Surface imperfections

Extracted from the DTI National Measurement Good Practice guide No 80 Fundamental Good practice in Dimensional Metrology. (Available from the National Physical Laboratory NPL Teddington, Middlesex, United Kingdom

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The GPS standard technical rules are organised into six chain links for any given characteristic 1. 2. 3. 4. 5. 6.

The rules, symbols and how to understand the specifications of product documentation Theoretical definitions of tolerances and their numerical values. Geometry of a nonideal, real workpiece defined in relation to tolerance symbols on the drawing. The conformance, non conformance of real workpiece deviations to specification taking into account measurement uncertainty General approach to measurement equipment types and requirements Calibration standards, procedures and requirements of the measuring equipment used and there link to National and international Standards

Extracted from the DTI National Measurement Good Practice guide No 80 Fundamental Good practice in Dimensional Metrology. (Available from the National Physical Laboratory NPL Teddington, Middlesex, United Kingdom)

Geometric Dimensioning and Tolerancing (GD&T) is a universal language of symbols, much like the international system of road signs that advise drivers how to navigate the roads. GD&T symbols allow a Design Engineer to precisely and logically describe part features in a way they can be accurately manufactured and inspected. To do this use is made of an engineering drawing or CAD model to provide the information An Engineering Drawing and CAD model has a purpose to show the required design function and therefore allow all parties involved to interpret the design requirements Geometric Dimensioning and Tolerancing (GD & T) is used in conjunction with standard dimensioning to describe the geometry of products and their relationship between various functional parts or assemblies The interpretation of the Technical Drawings using GD & T is done in various ways. The designer will make use of various symbols linked to different categories. Each option available to the designer should be defined by utilising some of the following;

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Ø

Feature Control Frames

Ø

Geometric Characteristics (Symbols)

Ø

Geometric References (Datum’s)

Ø

Tolerance Shapes

Ø

Tolerance Zones (Values)


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Feature Control Frames and Datum Definitions

IN THIS CHAPTER

Ø Ø Ø Ø Ø

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Feature Control Frames Datum’s Axis Plane Target


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Geometric tolerances are normally expresses by using a combination of feature control frames and datum reference symbols. Normally GD & T symbols will only be part of the dimensioning shown on the drawing or CAD model. Remember standard bilateral and unilateral tolerances will be shown along with other parameters about the surface texture requirements and material specifications. Geometric tolerances are defined within feature control frames. These frames are specifically designed. Some are relative to a datum reference, some are relative to themselves. The feature control frame is like a basic sentence that can be read from left to right. Examples of feature control frames are shown below;

Feature Control frames

Geometric Symbol of Control (Symbol)

Tolerance Zone and shape

Primary Datum Secondary Datum Tertiary Datum

1

No Datum Reference

2

3

Two Datum References

4

12

One Datum Reference

Three Datums References


The geometric symbol of control is specified on the left hand side. This will vary depending on the requirement and functionality required from the feature and component part The shape and tolerance within the feature control frame determine the limits of production variability. Datum examples The Primary Datum can be defined by a minimum of 3 point contact on a surface or by the generation of a 3D Axis through a minimum of 2 features. The Secondary Datum can be defined from a minimum of 2 points, of an edge or through an axis relative to the Primary datum The Tertiary Datum can be defined by a minimum of one point in relation to the Primary and secondary datum’s

Technical Drawing showing the datum definitions (Measurement terms: alignment or coordinate system)

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Technical Drawing showing the datum relationships

Feature Control Frames Definitions No Datum Reference

0.035 Single Datum Reference

0.085

A

0.145

AB

Multiple Datum Reference

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Two Datum Reference

0.200

A

B

Three Datum Reference

0.145 Tolerance zones over a specified length

0.01/100

0.01 mm over any 100 mm length

Combined Tolerance Zone

0.2 0.05/190 Overall tolerance 0.2 mm, 0.05 mm over any 190 mm length but

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Theoretically exact dimensions Dimension defining the theoretical exact position are defined in a box. Each of these dimensions should have a feature control frame attached at some stage to define a tolerance otherwise these dimensions should be produced perfectly to these sizes with no variation.

156 4 Ø 6.2

38°

Datum symbols The datum symbols used are normally specified as below. The use of a letter is the convention used of specified within the ASME and ISO standards

A

B

The datum symbols can be positioned in different places on a drawing to define the requirements of the component part. Each time the datum symbols are used this should tell the manufacturing and measurement departments how to set up the part. It is critical that the interpretation of this is correct to avoid any errors in the set up of both the machine tool and the measurement equipment used.

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Datum Axis

Datum Plane or extension Feature Outline

Feature Extension

A

Drawing examples of both axis and plane

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A

Axis and plane with the alternative option of specifying a datum

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Datum Targets Datum’s can be defined for manufacturing purposes as targets. Often used in the casting industry. They could be used to create the final datum’s of the component part. These targets are normally categorised as on of the following; Ø

Point

Ø

Line

Ø

Area

Point Datum target point from the corner is defined as below. This could be located on the component by the use of a predefined fixture

C

6 6

Line Datum target line from the corner is defined as below. This could be located on the component by the use of a predefined fixture

B1

B1

90

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Area Datum target areas from the corner are defined as below. These could be either circular or boxed as shown. This could be located on the component by the use of a predefined fixture

Ø9 A1 4

2x2 4A2

7

7

Three datum target areas specifying the primary datum ‘A’

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12 5 12

Two lines specifying the secondary datum ‘B’ and a point specifying the Tertiary datum ‘C’

Two diameters defining the Datum through a common axis

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Primary and secondary datum’s as checked by a gauge

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Form Tolerance

IN THIS CHAPTER

Ø Ø Ø Ø

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Circularity (Roundness) Straightness Flatness Cylindricity


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Circularity Circularity also known as Roundness — in this example the shape of the diameter to be produced and measured should be round within a tolerance zone of 0.040 The tolerance is specified by a zone bounded by two concentric circles The measurement of circularity can be achieved by different methods normally by a specific roundness measuring machine or by utilising Coordinate measuring machine software

Diameter varying within tolerance of size and form

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0.040

Circularity on a Taper

Circularity measurement example taken using a dial indicator, stand and vee block

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Circularity measurements taken using a roundness measuring machine

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Straightness Straightness can be defined as the maximum allowable deviation away from a straight line or axis within the tolerance zone Definition of tolerance zones

One direction

Two directions, different values

One direction, tapered diameter

One direction, cylindrical zone

One direction, possible shapes of part

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Flatness Flatness can be defined as the maximum allowable deviation on a surface within the tolerance zone

Tolerance zone across three surfaces

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Flatness definition

Measurement on surface table using 3 location supports and a dial indicator and stand

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Cylindricity Cylindricity can be defined as the maximum allowable deviation of all points on a surface of revolution equi distant from a common axis within the a tolerance zone defined by two cylinders

Cylindricity

0.025

0.040

0.025

0.040

Measurements taken using a roundness measuring machine

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Location Tolerances

IN THIS CHAPTER

Ø Ø Ø

Ø Ø

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Location Regardless of Feature size Maximum Material Condition(Maximum Material Requirement) Concentricity/Coaxiality Symmetry


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True Position Location tolerances are also known as true positional tolerances. Either defined as a cylindrical zone or parallelepiped (Boxed/rectangular)

Establishing dimensions

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Regardless of Feature Size (RFS) S Regardless of Feature Size (RFS) The symbol was used next to the tolerance, within the feature control frame in a previous ANSI standard

Cylindrical zone example

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Positional tolerance on an edge at a specific angle

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Bi directional positional tolerance of holes

Cylindrical tolerance zone on a pattern of holes

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Positional tolerance on a surface at a specific angle

Drawing example relative to three Datums

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Position of surface relative to Datums ‘A’ and ‘B’

RFS Calculation

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Actual centre position relative to the nominal centre position

Actual position calculation expressed as a diameter output

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Maximum Material Condition principle

M

Maximum Material Condition (MMC); A product feature has the most amount of material within the allowed tolerance zone Ø Internal feature is the smallest size allowable within the allowed tolerance zone Ø External feature the largest size allowable within the allowed tolerance zone . The MMC symbol M can be positioned within the tolerance frame either next to the tolerance or any datum symbol

M

Maximum Material Condition (MMC) is a basis used for the assembly of different products – for example a pin fitting into a hole or a manifold fitting onto studs. MMC provides the combination of the smallest hole and the largest pin, so as to fit together as an assembly. Once this has been established it is known as the Virtual Condition – the worst condition for the pin and hole to assemble. At virtual condition the two features would just fit and change from this could result in an easier fit between the two features. Virtual Condition is a boundary that is generated by the effects of combining the MMC and the Geometric Tolerance.

Ø

Internal: MMC Condition value minus the geometric tolerance External: MMC condition value plus the geometric tolerance Note; This is dependent on the features remaining within tolerance

of size. Note; MMC can be applied to other symbols such as the following; Straightness Circularity Angularity, Symmetry, Parallelism, Perpendicularity, Concentricity/ Co axiality and Position 39


Least Material Condition principle Least Material Condition (MMC); A product feature has the least amount of material within the allowed tolerance zone Ø Internal feature is the largest size allowable within the allowed tolerance zone Ø External feature the smallest size allowable within the allowed tolerance zone . The LMC symbol L can be positioned within the tolerance frame either next to the tolerance or any datum symbol

L

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Maximum Material Condition calculation on an actual feature

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Maximum Material Condition calculation on a datum Feature

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Maximum Material Condition calculation on both the actual and datum Features

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Projected Tolerance Zone P where the positional tolerance is projected out from the feature by a specified amount (40 and 60 in this example)

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Concentricity or Coaxiality Concentricity or Coaxiality is defined by the same symbol. All sectional features taken are defined as being common to the datum axis feature. As a simple explanation of the difference consider the geometric elements circle and cylinder, these can be defined as two dimensional and three dimensional features. Both Concentricity and Coaxiality can be thought of in the same terms.

Concentricity

Coaxiality of an axis to a multiple datum axis

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Coaxiality of axis D2 to axis D1 (cylindrical zone around axis)

Concentricity of outside diameter centre to datum A centre

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Deviation as calculated from and axis to axis

Measurement of concentricity on a roundness measuring machine

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Measurement of coaxiality on a roundness measuring machine

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Symmetry Symmetry also known the middle off or equal/equal about the centre. In the example the tolerance is applied to the median plane created by the two inside surfaces of the slot to datum ‘A’ created from the median plane of the two out side surfaces

Tolerance zone in one direction applied to the centre (median plane)

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The tolerance applied to the cross hole centre line is to the centre of datum axis ‘A’

Hole is on centre to multiple datum axes in two directions with different tolerances

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Hole is on centre to median plane created from two surfaces and slot is on centre to datum axis ‘A’

Measurement of slot on centre using Dial indicator, stand, vee blocks, surface plate and gauge block inserted into the slot

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Orientation Tolerances

IN THIS CHAPTER

Ø Ø Ø

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Parallelism Perpendicularity Angularity


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Parallelism Parallelism can be defined in many ways as shown below, whether applied to an axis or a surface

Tolerance zone defined by two parallel planes or lines relative to defined datum face A

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Tolerance zone defined by a cylindrical tolerance zone elative to the datum axis as defined by datum diameter ‘A’

Combining Flatness and Parallelism

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Effects of flatness when dealing with parallelism

Parallelism of a surface on centre line to a multiple datum defined by ‘A’ and ‘B’ (single direction)

Datum Parallelism of a diameter to an axis defined by ‘A’ (two tolerances in each direction)

Datum

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Parallelism of a diameter to an axis defined by ‘A’ (cylindrical tolerance zone)

Datum

Parallelism of an edge to a surface defined by ‘A’ (single direction)

Datum Parallelism of a surface to a diameter defined by ‘A’ (single tolerance across surface)

Datum

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Parallelism of a surface to a surface defined by ‘A’ (single tolerance across surface)

Datum

Parallelism of an edge to a surface defined by ‘A’ (single tolerance across surface and parallelism of and axis to an axis of two pins (cylindrical zone)

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Measurement of the parallelism of a diameter using a dial indicator, stand and surface plate

Measurement of the parallelism of a surface using a dial indicator, stand and surface plate supported of the axis of datum ‘A’

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Perpendicularity Perpendicularity can be defined in many ways as shown below, whether applied to an axis or a surface

Perpendicularity tolerance applied to a surface or edge where the feature is to be at 90 degrees to datum face ‘A’

0.200

A

A

Perpendicularity tolerance applied to the axis defined by both sides or a diameter 0.200

A

A

60


Perpendicularity of an axis to a surface with the tolerance in two directions

Datum axis

Datum surface Perpendicularity of an axis to a surface with the tolerance in one directions and surface to a surface

Datum axis

Datum surface 61


Perpendicularity tolerance applied to an axis to a surface with different tolerances in two directions.

Datum surface

Perpendicularity of an axis to a surface (cylindrical tolerance zone)

Datum surface

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Drawing example of deviation

Perpendicularity Measurement of the actual surface with a precision or cylindrical square

63


Perpendicularity Measurement of the actual axis to the datum surface using a dial indicator, stand and surface table

An alternative method of measuring Perpendicularity is by means of a laser or auto collimator. Calibration of CMM’s is often done by the laser method

64


Angularity Angularity is a method of checking the deviation of a surface or an axis at a specified angle

Angularity specified as a surface to a surface or a surface to an axis

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Measurement of angularity using a dial indicator, stand, surface plate and an angle gauge. An alternative measurement method is to use a Sine Bar

Angularity of a centre line to an axis

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Angularity of a surface to an axis

Angularity of a surface to a surface

Measurement of angularity using a protractor or clinometer

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68


Profile

IN THIS CHAPTER

Ø Ø

69

Profile of a line Profile of a surface


7

Profile Profile tolerances fall into two main categories Ø

Profile of a Line

Ø

Profile of a surface

These tolerances are normally applied to irregular or normal edges, surfaces or, arcs. The tolerance can be applied either side of the nominal profile (Bilateral) or to one side (unilateral) only. The uniform boundary can be applied relative to the profile only or alternatively can be applied relative to the datum reference system as well as the profile.

Total Tolerance Nominal profile

Total Tolerance

Nominal profile UniLateral (Internal or External)

Bilateral Tolerance

Tolerance of form only

Tolerance of form and location

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Profile of a line tolerance on the form only as indicated

Profile of a surface tolerance on the form of the spherical radius

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72


Runout Tolerances

IN THIS CHAPTER

Ø Ø Ø

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Runout Circular Runout Total Runout


8

Runout Runout is applied to control any circular feature surfaces rotated through 360 degrees. This could apply to a diameter or a surface at any position across that surface of revolution

Circular runout is applied the surface around the datum axis, included within the tolerance are any effects of concentricity and circularity. Axial runout is applied to the surface adjacent to the axis around the datum axis, included within the tolerance are the effects of flatness and Perpendicularity at the position where the results are obtained

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Circular Runout example

Axial Runout example

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Runout tolerance applied to both datum ‘A’ and ‘B’ unable to generate an axis from datum ‘B’

Runout of surface rotated around the axis through datum diameter ‘A’

Runout of tapered surface rotated around the axis through datum diameter ‘A’

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Runout of curved surface rotated around the axis through multiple datum diameters ‘A’ and ‘B’

Runout of outside diameter rotated around the axis through multiple datum diameters ‘A’ and ‘B’

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Runout of the surface rotated around the common axis datum diameters ‘A’ , where datum ‘A’ is defined by locating the component part between centres

Measuring Runout using centres or vee block and dial indicators

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Measuring Runout of a tapered diameter a using centres or vee block and dial indicators

Runout of a diameter to a multiple datum defined through the axis of datum diameters ‘A’ and ‘B’ where ‘A’ and ‘B’ are at a set distance as defined by the boxed dimension

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Total Runout Total Runout controls the surfaces around the axis of 360 degrees revolution. The difference from runout is that this tolerance is applied across the complete surface as one tolerance. As a composite tolerance total runout includes the effects of circularity, Cylindricity, concentricity Coaxiality Perpendicularity, Parallelism, and Flatness

Total runout applied to a Plane surface around an axis of revolution

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Total runout applied to a cylinder around an axis of revolution

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Total circular Runout of outside diameter along its length to the axis created through multiple datum diameters ‘A’ and ‘B’

Total Runout across the surface to the axis created through datum diameter ‘D’

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Appendix

IN THIS CHAPTER

Ø Ø Ø Ø

83

Further MMC options Basic Symbols References Hexagon Contacts


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MMC applied to Straightness

MMC applied to Perpendicularity

84


Maximum Material Condition (MMC) and Least Material Condition (LMC)

85


Maximum Material Condition (MMC) applied to two diameters floating

If the two diameters are at their maximum size then the centre position can vary as shown applying a 0.1 tolerance around each diameter

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If the two diameters are at their minimum size then the centre position can vary as shown applying a 0.1 tolerance around each diameter plus the 0.2 tolerance of size (0.1/side on each diameter)

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Basic Symbols Form

Symbol

Circularity Basic Dimension Straightness

38°

156

Flatness

Ø 6.2 Cylindricity

Location True Position Maximum Material Condition Least Material Condition Projected tolerance

Datum Reference M L P

A

Orientation Parallelism Feature Control Frame Perpendicularity Angularity Concentricity/Coaxiality Symmetry

Profile and Runout Profile of a line Profile of a surface

References; More detailed information is available from various standards throughout the world. As an example Ø ASME Y14.5 Ø BS8888:2004 Technical Product Specifications (TPS)

Runout Total Runout

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Examples of ISO standards used Ø ISO:1101 Ø ISO 2692


Hexagon Details

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GdT _Theory_1st Principle_ Training Manual LEVEL 1

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