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
Copyright 2003 Joseph Greene All Rights Reserved
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GD&T
• Topics
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Introduction
History
Feature Control Frames
Material Condition Modifiers
Form Tolerances
Datums
Orientation Tolerances
Runout
Profiles
Position Tolerances
Applications
Copyright 2003 Joseph Greene All Rights Reserved
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Some Greek Letters
• Alpha: 
•
Nu: 
• beta: 
•
xi: 
• gamma: 
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• delta: 
omicron: 
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pi: 
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rho: 
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sigma: 
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tau: 
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upsilon: 
• kappa: 
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phi:
• lamda: 
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chi: 
• mu: 
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psi: 
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omega:
• epsilon: 
• zeta: 
• eta: 
• theta: 
• iota:

Copyright 2003 Joseph Greene All Rights Reserved
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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 a
manufacturable 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.
Copyright 2003 Joseph Greene All Rights Reserved
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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 A
presented 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.
Copyright 2003 Joseph Greene All Rights Reserved
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• Introduction
GD&T
– 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 (tolerances
are +/-)
– 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 of
changes are between $2500 and $20,000.
Copyright 2003 Joseph Greene All Rights Reserved
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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.
Copyright 2003 Joseph Greene All Rights Reserved
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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 exact
locations 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.
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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 sequence
lists 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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GD&T vs. Coordinate Measuring
• What is a quality drawing (continued)
– 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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GD&T vs. Coordinate Measuring
• What is a quality drawing (continued)
– 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 Pharaoh’s forearm.
– Span: the distance form the tip of the thumb to the tip of the little
finger,
– Standard meter
• 1789: One- ten millionths of the distance from North Pole to the equator
measured through Paris France.
• 1906: U.S. Prototype Meter number 27-as a “value of 1,553,164.13 times
the wavelength of cadmium red in air, at 760 mm of atmospheric pressure at
15 °C.”
• The continual change in the definition of the measurement is to increase the
accuracy of the meters length.
• The current definition of “the meter is the length of the path traveled by
light in vacuum during a time interval of 1/299,792,458 of a second.”
– The standardizing of dimensioning and tolerancing has paralleled
the development of a more accurate unit of measure
Copyright 2003 Joseph Greene All Rights Reserved
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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 of
Mechanical 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 fabricator
what 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 to
inspect form.
– GD&T uses symbols to communicate the information to those involved in
making the part to eliminate any misunderstanding.
– Word explanations can be confusing especially with the global market and the
translations of words into different languages.
– A simple layout of the symbols used in GD&T can be found in below.
Copyright 2003 Joseph Greene All Rights Reserved
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GD&T Definitions and Terms
• Feature Control Frames
• 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 for
that 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.
Geometric Characteristic
Symbol
 .005
Geometric Tolerance
Figure 3a-1 Simple
Feature Control Frame
Copyright 2003 Joseph Greene All Rights Reserved
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GD&T Material Condition Modifiers
• 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.
Copyright 2003 Joseph Greene All Rights Reserved
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GD&T Material Condition Modifiers
• Maximum Material Condition (MMC) External
– Indicates that the tolerance given applies only at the maximum amount of
material 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 or
maximum amount of material, as shown in Figure 3b.ii.1.
MMC for External Features
• 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.
Figure 3b.ii.2 MMC for Internal Feature
– The feature control from the symbol o represents MMC
Copyright 2003 Joseph Greene All Rights Reserved
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GD&T Material Condition Modifiers
• Least Material Condition (LMC) External
– Indicates that the tolerance given applies only at the least amount of material for
that 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.
LMC for External Features
• Least Material Condition (LMC) Internal
– LMC is at the smallest limit, or least amount of material, as shown
LMC for
Features
– The feature control from
theInternal
symbol
 represents LMC
Copyright 2003 Joseph Greene All Rights Reserved
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GD&T Form 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 to
perfectly 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
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GD&T Straightness
• Straightness
Straightness Applied to a Cylinder Surface and Cylinder
• 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.
Copyright 2003 Joseph Greene All Rights Reserved
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GD&T Flatness
• Flatness
– A perfectly flat surface must contain all elements in one plane.
– The flatness tolerance establishes a set of parallel planes that must
contain 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
Copyright 2003 Joseph Greene All Rights Reserved
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GD&T Circularity
• Circularity
– Controls the roundness of any feature with circular cross section.
• The circular cross-section must be taken perpendicular to the axis of the
cylinder 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
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GD&T Cylindricity
• 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
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GD&T Datums
• 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 by
which toolmakers and machinists create the part and inspectors check the
part to the print.
• Datum features are 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.
Copyright 2003 Joseph Greene All Rights Reserved
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GD&T Datum Identification
• Datum Identification
– A datum feature is identified by using the datum symbol combined
with a datum feature triangle.
Datum Symbol and Application
– 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 Target Symbol and Application
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GD&T Orientation 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
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GD&T Parallelism
• 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
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GD&T Parallelism
• 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 Applied to an Axis
– 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 Line Elements
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GD&T Perpendicularity
• Perpendicular geometric tolerance
– Two parallel planes of cylindrical zones that are a basic 90 to a
datum plane where the surface or axis of the feature must lie.
– The symbol for perpendicularity is 
Perpendicular Tolerance Feature Control Frame
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GD&T Perpendicularity
• The examples below give different applications of
perpendicularity geometric tolerance.
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–
–
–
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 a Surface
Perpendicularity to an Axis
Perpendicularity to a Center Plane
Perpendicularity to Line Elements
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GD&T Angularity
• Angularity geometric tolerance
– A surface, center-plane or axis at a specified angle (other than 90)
form a datum plane or axis.
– The symbol for angularity is 
Angularity Tolerance Feature Control Frame
– Figure 1 the application of angularity to a surface.
– Figure 2 is the application of angularity to an axis.
– Figure 3 is the application of angularity to a center plane.
Angularity to a Surface
Angularity to an Axis
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Angularity to a Center Plane
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GD&T Runout 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 Runout and Total-Runout.
– Of these two types of Runout,
– Circular Runout is the less complex.
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GD&T Circular 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 to
an 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
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GD&T Circular 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 cylindrical
surface.
• Figure 2 gives the application of circular runout as applied to a noncylindrical feature.
• Figure 3 gives the application of circular runout as applied to face surfaces.
Circular Runout Applied to a Cylindrical Surface
Circular Runout Applied to a Non-Cylindrical Surface
Circular Runout Applied to a Face Surface
Copyright 2003 Joseph Greene All Rights Reserved
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GD&T Total 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
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GD&T Total 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
datum’s 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
Copyright 2003 Joseph Greene All Rights Reserved
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GD&T Profile Tolerances
• Profile tolerance
– The outline of an object represented either by an external view or
by a cross section through the object.
– Profile tolerances may be used to control form, orientation and
location.
• The manner in which the profile tolerance is applied,
– How it is dimensioned, and
– How datum’s are utilized all effect the level of control desired by using
profile tolerances.
• There are two profile tolerance types,
– Profile of a line and profile of a surface.
– Note: when the profile is other than flat, basic dimensions must be used
to describe the profile.
» A basic dimension is depicted with a box around the dimension and
is considered an exact dimension
Copyright 2003 Joseph Greene All Rights Reserved
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GD&T Profile 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 is e.
– Figure shows the feature control frame for profile of a line
geometric tolerance.
Profile of a Line Feature Control Frame
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GD&T Profile Tolerances
• Profile of a Line
– Many automobile companies use an exact profile to gage sheet
metal parts that have changing cross sections.
• The hood of an automobile is a good example of such a cross section that
has a changing profile.
• The profile tolerance is assumed a bilateral tolerance, which is the tolerance
both above and below the true profile line.
• The following examples give usage of the profile of a line tolerance.
Figure. Cross section of a Figure 2. Uses profile of a line to Figure 3 is a special case
simple contour that is
control all around a cross section of using profile of a line
controlled by line profile
for a unilateral
of a wing.
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tolerance.
specification.
Copyright 2003 Joseph Greene All Rights Reserved
GD&T Profile 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&T Profile 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 it’s 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
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Figure 2
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GD&T Positional Tolerances
• Position tolerances
– Locate features from datum’s 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
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