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Copyright 2003 Joseph Greene All Rights Reserved1

MFGT 124

Solid Design in Manufacturing

GD&T

Professor Joe Greene

CSU, CHICO

Reference: A. Kruilikowski, Effective Training, Inc.Manufacturing

Engineering, 27 (Feb 1994)

MFGT 124

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GD&T Topics

Introduction

History

Feature Control Frames

Material Condition Modifiers

Form Tolerances Datums

Orientation Tolerances

Runout

Profiles Position Tolerances

Applications

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Some Greek Letters

Alpha:

beta:

gamma:

delta:

epsilon:

zeta: eta:

theta:

iota:

kappa: lamda:

mu:

Nu:

xi:

omicron:

pi:

rho:

sigma: tau:

upsilon:

phi:

chi:

psi:

omega:

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GD&T

Introduction

Drawing quality is an important issue for manufacturing

Flawed drawings can cause mistakes in the product.

Poor drawings can easily double manufacturing costs and delivery time.

Most manufacturing and quality engineers agree that

50% of the drawing they see are flawed and

Require 5 to 10 engineering changes before they define amanufacturable part.

Common problems include:

Undefined reference frames.

Inadequate or overly restrictive tolerances.

Frequently, manufacturing makes assumptions about the intent of the design

engineer and problems ensue.

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GD&T

Introduction

Creating unambiguous part drawings is a demanding thought

process.

Function of part and process to manufacture and inspect it must be

thoroughly understood and communicated.

Example,

Design engineer intends for the part to be inspected with side Apresented to the gage first, with side B as a secondary point of contact,

Inspector puts Side B to the gage first, and A as secondary point.

Results:

Good parts are scrapped since the are measured as out of spec, but

they might be OK.

Bad parts are shipped off since they pass the inspection.

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GD&T Introduction

Creating detailed GD&T drawings take more time and are more

expensive to make than coordinate dimension drawings. Coordinate dimensional drawings are faster to draw and less expensive,

But have more errors on it and can cause manufacturing problems.

Example,

Designer 1 creates drawings with coordinate drawing standards (tolerancesare +/-)

Time is 20 hours for part A.

Cost is $50/hr x 20 hours = $1000.

Designer 2 creates drawing with ASME Y14.5M (GD&T Standards)

Time is 30 hours for part A.

Cost is %50/hr x 30 hours = $1500.

Revisions to correct design problems.

Paperwork cost range for $500 to $2000 per change.

If 5 to 10 changes are needed to correct designer 1 then costs ofchanges are between $2500 and $20,000.

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7/40Copyright 2003 Joseph Greene All Rights Reserved7

GD&T vs. Coordinate Measuring What is a quality drawing?

Compare two drawing styles

Figure 1. GD&T example.

Figure 2. Coordinate dimensioning example of same part.

Part straightness

Both drawings specify a part thickness of 0.25 inches +-0.010.

How straight must the part be?

Fig 1 has GD&T straightness symbol applied to thickness (Area A)

Symbol on part means that the part must be straight enough to pass

between two parallel plates spaced 0.260

Fig 2 has coordinate version says nothing about straightness.

Part could be within thickness tolerance, yet significantly bowed .

Note needs to be added to drawing to require straightness.

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GD&T vs. Coordinate Measuring What is a quality drawing (continued)

Unwanted tolerance accumulation

Fig 1 includes several dimensions (B) called basic dimensions which identify exactlocations from which tolerances are specified.

Fig 2 has no corresponding term and tolerances can accumulate.

Another note needs to be added Dimensions are gage dimensions.

Part inspection Figure 3.

Different inspection points and procedures can lead to different measurements.

GD&T establishes an order of measurement sequence. Coordinate measuring does not.

Two inspectors can get totally different results from same part.

GD&T system

Specifies measurement sequence.

Parts intended to contact gage are datums. (C Fig 1) Geometric tolerance controlling hole locations defines the sequence in which

part surfaces must touch the gage surfaces. (D)

Reading from left side of positional tolerance callout, the letter sequencelists the order in which the part touches the gage. A, B, C

Coordinate measuring system has no equivalent system and as such requires a note.

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Hole location

GD&T system (D) contains a symbol (circle with slant in it) that denotes the

shape of the tolerance zone as a diameter.

Same geometric tolerance includes a circled M symbol (Maximum

material condition) that permits the location tolerance to increase for

larger holes.

Coordinate measuring system show two ways in which is inadequate:

Uses square tolerance zones, Fig 4, which allow more tolerance for hole

centers diagonally than vertically or horizontally. Round tolerance zone

is better.

Requires tolerance zone for hole location to remain fixed in size,regardless of hole size.

Small holes have same tolerance zones as larger diameters.

Notes have to be added for round tolerance.

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Counterbore location

GD&T specifies counterbore diameter, depth, and location.

Includes position symbol under counterbore, E.

Specifies location relative to small diameter

Coordinate version only specifies bore diameter and depth, allowing user to

choose between Following smaller diameter location, or

Locating by tolerance dimension for both diameters.

Note must be added to ensure proper location.

Equivalent information on Coordinate Measuring drawing

Fig 6

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GD&T History In ancient Egypt,

Cubit: unit of measure based on length of the Pharaohs forearm.

Span: the distance form the tip of the thumb to the tip of the littlefinger,

Standard meter 1789: One- ten millionths of the distance from North Pole to the equator

measured through Paris France.

1906: U.S. Prototype Meternumber 27-as a value of 1,553,164.13 timesthe wavelength of cadmium red in air, at 760 mm of atmospheric pressure at15 C.

The continual change in the definition of the measurement is to increase theaccuracy of the meters length.

The current definition of the meter is the length of the path traveled bylight in vacuum during a time interval of 1/299,792,458 of a second.

The standardizing of dimensioning and tolerancing has paralleledthe development of a more accurate unit of measure

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GD&T Standards ANSI Y14.5

The ANSI standard was revised in 1982.

In 1994, the standard was moved form ANSI to the American Society ofMechanical Engineers (ASME) and the name changed to ASME Y14.5.

The standard was also revised into its current form of ASME Y14.5-1994.

Geometric Dimensioning and Tolerancing (GD&T) Establishes the standard by which designers can communicate

the intended function of the part to the machinist making the part and the inspector checking the part.

This standard lets the designer inform the machinist, toolmaker or fabricatorwhat are the important features of the design when they are making the part.

The standard also lets the inspector know what are the important features toinspect form.

GD&T uses symbols to communicate the information to those involved inmaking the part to eliminate any misunderstanding.

Word explanations can be confusing especially with the global market and thetranslations of words into different languages.

A simple layout of the symbols used in GD&T can be found in below.

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GD&TDefinitions and Terms

Feature Control F rames

Geometric Tolerance Geometric Characteristic Symbol The feature control frame helps to organize the various symbols into a

sentence.

This sentence communicates the information in an organized manner.

The first is the Geometric Tolerance is the total tolerance band forthat feature.

This means that it is not a +/- tolerance.

An example of this is if we have a dimension of 1.00 and a Geometric

tolerance of .005, we can interpret this as 1.000 +/-.0025.

Figure 3a-1 Simple

Feature Control Frame

Geometric Characteristic

Symbol

Geometric Tolerance

005.

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GD&TMater ial Condition Modif iers Material Condition Modifiers

Indicate at what material condition the tolerance is applicable.

There are three different types of material condition modifiers

Regardless of Feature Size (RFS)

Used if the tolerance is to be met at all possible sizes of the feature

to be produced.

In the current standard, this is assumed if one of the other modifiers

is not specified. In the older standards, the symbol was placed in

the feature control frame to designate the RFS condition.

G &

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GD&TMater ial Condition Modif iers Maximum Material Condition (MMC) External

Indicates that the tolerance given applies only at the maximum amount ofmaterial for that feature. For holes, it is the smallest diameter-Max material

The key words in this modifier are maximum material.

When working with external features the MMC is at the largest limit ormaximum amount of material, as shown in Figure 3b.ii.1.

Maximum Material Condition (MMC)- Internal When working with internal features the MMC is at the smallest limit, or

maximum amount of material, as shown in Figure 3b.ii.2.

The feature control from the symbol orepresents MMCFigure 3b.ii.2 MMC for Internal Feature

MMC for External Features

GD&T C f

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GD&TMater ial Condition Modif iers Least Material Condition (LMC) External

Indicates that the tolerance given applies only at the least amount of material forthat feature. For diameters, it is the smallest diameter. For holes, it is the biggest

diameter-Min material When working with external features the LMC is at the largest limit or least

amount of material, as shown below.

Least Material Condition (LMC)Internal LMC is at the smallest limit, or least amount of material, as shown

The feature control from the symbol represents LMCLMC for Internal Features

LMC for External Features

GD&T F T l

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GD&TForm Tolerances Form tolerances

The control the variations of individual features of a part.

Such features include straightness, flatness, circularity and Cylindricity. Form tolerances do not control the relationship between features.

Straightness

The straightness tolerance controls all the elements along a

theoretical straight line on a surface or axis. The tolerance given for straightness specifics how close toperfectly straight the feature must be created.

Depending on the way straightness is defined on the drawing, determines

whether surface elements or an axis is to be controlled.

The symbol for straightness is

Straightness Applied to a Surface

GD&T St i ht

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GD&TStraightness Straightness

Note that straightness is applied only to the view that it is

defined on a drawing The placement of the feature control frame is very important.

Straightness Applied to a Cylinder Surface and Cylinder

GD&T Fl t

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GD&TFlatness Flatness

A perfectly flat surface must contain all elements in one plane.

The flatness tolerance establishes a set of parallel planes that mustcontain all elements of the surface.

The flatness tolerance is not used in conjunction with a material

modifier or datum reference it is a stand-alone tolerance.

The symbol for flatness is . Example, gives the different representations of how flatness tolerance is

used in conjunction with a feature control frame.

Two Flatness Tolerance Callout Methods

GD&T Ci l it

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GD&TCircularity Circularity

Controls the roundness of any feature with circular cross section.

The circular cross-section must be taken perpendicular to the axis of thecylinder or cone, or through a common center of a sphere.

Circularity tolerance is also referred to as the roundness tolerance.

The symbol for Circularity is c. The tolerance zone for a circularity tolerance is bounded by two concentric

circles.

The tolerance value is determined by the radial distance between the circles,

not the distance between the diameters.

Example gives a typical call-out for circularity tolerance.

Circularity Form Tolerance Call-Out

GD&T C li d i it

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GD&TCylindricity Cylindricity

Controls the surface of a cylinder.

This tolerance can be applied to a shaft or a hole. Cylindricity is identified by a radial tolerance zone that establishes

two perfectly concentric cylinders.

The surface of the cylinder that the tolerance is applied to must lie

within this tolerance zone.

The cylindricity tolerance also controls the parallelism of the sides

of the cylinder to prevent the part form being tapered.

Example gives a typical call-out for cylindricity tolerance.

Cylindricity Form Tolerance Call-Out

GD&T D t

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22

GD&TDatums Datums

Theoretically perfect planes, surfaces, points, lines or axes that are

derived form a datum feature. Datums are used by designers to specify important features of reference bywhich toolmakers and machinists create the part and inspectors check the

part to the print.

Datum featuresare actual features of the part, such as a surface, that

establish the datum.

The feature control frames that define tolerances based on datum features

include datum references.

Datums are used to establish an inspection point from a surface.

Checking jigs and fixtures are built based upon datums to inspect

parts.

GD&T D t Id tifi ti

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23

GD&TDatum Identification Datum Identification

A datum feature is identified by using the datum symbol combined

with a datum feature triangle.

A datum target symbol is a circle with a horizontal line across it, with the bottom half of the circle used to identify the datum target and the

top is empty except when specifying the diameter of a datum target area.

Datum Symbol and Application

Datum Target Symbol and Application

GD&T O i t ti T l

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GD&TOrientation Tolerances Orientation tolerances

Control the relationship of features to one another.

Orientation tolerances include parallelism, perpendicularity and angularity. Orientation tolerances are datum related and may be applied with

material modifiers MMC or LMC.

RFS material modifier is always implied unless otherwise stated.

Parallelism Defined as two parallel planes of cylindrical zones that are parallel

to a datum plane where the surface or axis of the feature must lie.

The symbol for parallelism is

Parallelism Tolerance Feature Control Frame

GD&T P ll li

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GD&TParallelism Parallelism

There are three main types of parallelism

call-outs, surface, axis and line. When a surface is to be parallel to a datum, the feature control

frame is either connected by a leader to the surface or directly

connected to the extension line of the dimension.

Parallelism Applied to a Surface

GD&T P ll li

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GD&TParallelism Parallelism

When parallelism is applied to an axis the axis of the hole may be

specified within a tolerance zone that is parallel to a given datum. The feature control frame is place with the diameter dimension

Parallelism to line elements. When it is desirable to control only individual line elements, rather than the

entire surface, the note EACH ELEMENT or EACH RADIAL

ELEMENT

Parallelism Applied to an Axis

Parallelism Applied to Line Elements

GD&T Perpendic larit

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GD&TPerpendicularity Perpendicular geometric tolerance

Two parallel planes of cylindrical zones that are a basic 90to a

datum plane where the surface or axis of the feature must lie. The symbol for perpendicularity is

Perpendicular Tolerance Feature Control Frame

GD&T Perpendicularity

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GD&TPerpendicularity The examples below give different applications of

perpendicularity geometric tolerance.

Figure 1 is the application of perpendicularity to a surface. Figure 2 is the application of perpendicularity to an axis.

Figure 3 is the application of perpendicularity to a center plane.

Figure 4 is the application of perpendicularity of line elements.

Perpendicularity to an AxisPerpendicularity to a Surface Perpendicularity to a Center Plane

Perpendicularity to Line Elements

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GD&T Runout Tolerances

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GD&TRunout Tolerances Runout

Combination of geometric tolerances used to control the

relationship of one or more features of a part to a datum axis. The geometric tolerances associated with Runout Form, Orientation and Location tolerances.

The features that may be controlled by Runout are surfaces around, or

perpendicular to, a datum axis.

There are two types of Runout error, Circular Runoutand Total-Runout.

Of these two types of Runout,

Circular Runoutis the less complex.

GD&T Circular Runout

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GD&TCircular Runout Circular runout

Is the error on a single circular element and provides the control of

these elements on a surface. The surface must have circular cross sections that are controlled relative toan axis of rotation.

Typical surfaces that are controlled by circular runout include

cylinders, cones, spherical surfaces and flat surfaces.

The symbol for circular runout is .

Circular Runout Tolerance Feature Control Frame

GD&T Circular Runout

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GD&TCircular Runout Circular runout

The following three examples give some of the different

applications of circular runout. Figure 1 gives the application of circular runout as applied to a cylindricalsurface.

Figure 2 gives the application of circular runout as applied to a non-

cylindrical feature.

Figure 3 gives the application of circular runout as applied to face surfaces.

Circular Runout Applied to a Face Surface

Circular Runout Applied to a Cylindrical Surface

Circular Runout Applied to a Non-Cylindrical Surface

GD&T Total Runout

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GD&TTotal Runout Total runout

Is the variation across the entire surface of a cylindrical feature or

perpendicular face surface. Total runout is used to control the combined variations of circularity, straightness, coaxiality, angularity, taper and profile when

applied to surfaces around and at right angles to a datum axis.

The symbol for total runout is .

Circular Runout Tolerance Feature

GD&T Total Runout

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GD&TTotal Runout Total runout

Note that total runout cannot be applied to conical or curved

surfaces as can circular runout. The following two examples give some of the different

applications of total runout. Figure 1 gives the application of total runout as applied to a cylinder.

The total runout feature control frame, in this figure, references a

compound datum of A and B. When checking the feature that references a compound datum both

datums A and B must be used together to establish an axis of rotation.

Figure 2 gives the application of total runout as applied to face surfaces.

Total Runout Applied to a Cylinder with Compound Datum Total Runout Applied to a Face Surface

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GD&T Profile Tolerances

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GD&TProfile Tolerances Profile of a Line

A two-dimensional cross section tolerance that extends along the

length of the feature. The line profile tolerance is used where parts have changing cross

section along their length and do not have to be along the entire

feature.

The symbol for profile of a line ise.

Figure shows the feature control frame for profile of a linegeometric tolerance.

Profile of a Line Feature Control Frame

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GD&TProfile Tolerances Profile of a Surface

Used to control all the elements of a surface and treats them as a

single entity. Profile of a surface, as its definition states, covers all points on a

surface in three dimensions.

The symbol for profile of a surface is f.

Figure shows the feature control frame for profile of a line

geometric tolerance.

Profile of a Surface Feature Control Frame


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GD&TProfile Tolerances Profile of a Surface

As with profile of a line, profile of surface can be measured with a

mater gage to control features of the surface or profile. The following examples give usage of the profile of a surface

tolerance. Figure 1 is a cross section of a plate with a slot. The slot is controlled by a

profile of a surface tolerance. That means that the depth of the slot as well

as its cross sectional profile is controlled. Figure 2 uses profile of a surface to control the surface of a part similar to

that seen in figure 3g.i.2.

Figure 1 Figure 2

GD&T Positional Tolerances

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GD&TPositional Tolerances Position tolerances

Locate features from datums or for establishing coaxiality or symmetry.

Positional tolerances define A zone where the center, axis or center plane of a feature of size is permitted to

vary form true position.

The true position is the theoretically exact position of the feature.

Basic dimensions are used to establish the location of the feature in

relationship to datum features. When using positional tolerances MMC and LMC must be specified in the

feature control frame after the tolerance otherwise RFS is assumed. Positional tolerances are also applied only to features of size; they are not applied to

features of form.

The format for the positional feature control frame is given below.

Position Tolerancing Feature Control Frame

Documents

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