# Geometric Dimensioning and Tolerancing

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Geometric Dimensioning and Tolerancing

A LOCATION TOLERANCE FORM TOLERANCES GDT PROBLEMS

Are all of these auto parts made in the same factory by the same company?

What is the purpose of GDT?
It is used on mating parts in order to assure that they are ‘interchangeable’.

Where did GDT come from? THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS (ASME) CREATED A GLOBAL STANDARD TITLED ASME Y FOR DIMENSIONING AND TOLERANCING.

SPEED LIMIT 65 40 MINIMUM What does this sign mean?

65 What are the LIMITS? What happens if you go out of that zone?
Any speed in between the limits is within the acceptable range or zone. SPEED LIMIT 65 40 MINIMUM UPPER LIMIT MAX. MIN. LOWER LIMIT What happens if you go out of that zone?

What is the TOLERANCE? The difference between the upper and lower limit equals the Tolerance zone. 65 UPPER LIMIT -40 LOWER LIMIT 25 = TOLERANCE ZONE SPEED LIMIT 65 40 MINIMUM 25 Tolerance = is the total amount that a dimension is permitted to vary.

What are the LIMITS? 12 .7 5 12.50 + 0.25 12 .25 SPECIFIED DIMENSION
TOLERANCE LIMITS

MMC & LMC MAXIMUM MATERIAL CONDITION AND LEAST MATERIAL CONDITION

What is the difference between these two glazed doughnuts?
Both of these doughnuts cost 90 cents. Which one is the best buy? Why? Which one was made with the most or maximum amount of dough? M MMC = Maximum Material Condition LMC = Least Material Condition L

M MAXIMUM MATERIAL CONDITION (MMC) = IS WHERE A FEATURE CONTAINS THE MAXIMUM AMOUNT OF MATERIAL PERMITTED WITHIN THE STATED LIMITS. (SEE BOOK EXAMPLE 1-8 & 1-9) 1 . 75 1 . 73 n Look at the limits of the O.D. and the I.D. of the washer. Which ones represent the washer at MMC? 0. 75 0. 73 n

n n 1 . 75 MMC OF THE O.D. 1 . 73 0. 75 0. 73 MMC OF THE I.D. M
MAXIMUM MATERIAL CONDITION (MMC) = IS WHERE A FEATURE CONTAINS THE MAXIMUM AMOUNT OF MATERIAL PERMITTED WITHIN THE STATED LIMITS. (SEE BOOK EXAMPLE 1-8 & 1-9) 1 . 75 1 . 73 MMC OF THE O.D. n 0. 75 0. 73 n MMC OF THE I.D.

L LEAST MATERIAL CONDITION (LMC) = IS WHERE A FEATURE CONTAINS THE LEAST AMOUNT OF MATERIAL PERMITTED WITHIN THE STATED LIMITS. (SEE EXAMPLE 1-10, 1-11) 1 . 75 1 . 73 n Look at the limits of the O.D. and the I.D. of the washer. Which ones represent the washer at LMC? 0. 75 0. 73 n

n n 1 . 75 LMC OF THE O.D. 1 . 73 0. 75 LMC OF THE I.D. 0. 73 L
LEAST MATERIAL CONDITION (LMC) = IS WHERE A FEATURE CONTAINS THE LEAST AMOUNT OF MATERIAL PERMITTED WITHIN THE STATED LIMITS. (SEE EXAMPLE 1-10, 1-11) 1 . 75 1 . 73 n LMC OF THE O.D. 0. 75 0. 73 LMC OF THE I.D. n

n n 1 . 75 MMC OF THE O.D. 1 . 73 0. 75 0. 73 MMC OF THE I.D. M
MAXIMUM MATERIAL CONDITION (MMC) = IS WHERE A FEATURE CONTAINS THE MAXIMUM AMOUNT OF MATERIAL PERMITTED WITHIN THE STATED LIMITS. (SEE BOOK EXAMPLE 1-8 & 1-9) 1 . 75 1 . 73 MMC OF THE O.D. n 0. 75 0. 73 n MMC OF THE I.D.

RFS Sometimes a geometric tolerance will be applied to a dimension at its MMC or it LMC. However……….. REGARDLESS OF FEATURE SIZE (RFS) = IS THE TERM USED WHEN A GEOMETRIC TOLERANCE OR DATUM APPLIES AT ANY INCREMENT OF SIZE WITHIN ITS UPPER OR LOWER LIMIT. (SEE EXAMPLE 4-7)

Review IT IS A GLOBAL STANDARD FOR DIMENSIONING AND TOLERANCING.
1. What does ASME Y stand for?  IT IS A GLOBAL STANDARD FOR DIMENSIONING AND TOLERANCING. 2. What is tolerance? IT IS THE TOTAL AMOUNT THAT A DIMENSION IS PERMITTED TO VARY.  3. What are limits?  ARE THE LARGEST AND SMALLEST (THE MAXIMUM AND MINIMUM) NUMERICAL VALUE THAT A FEATURES DIMENSIONS CAN BE. 4. How do they differ?  TOLERANCE IS THE DIFFERENCE BETWEEN A DIMENSIONS UPPER AND LOWER LIMITS. 5. What is meant by Maximum Material Condition? IS WHERE A FEATURE CONTAINS THE MAXIMUM AMOUNT OF MATERIAL PERMITTED WITHIN THE STATED LIMITS. 6. What is meant by Least Material Condition? IS WHERE A FEATURE CONTAINS THE LEAST AMOUNT OF MATERIAL PERMITTED WITHIN THE STATED LIMITS.  7. What is meant by RFS? REGARDLESS OF FEATURE SIZE

Symbols

Geometric Chacteristic Symbols

Feature Control Frame A SYMBOL MADE UP OF COMPARTMENTS CONTAINING THE GEOMETRIC CHARACTERISTIC SYMBOL AND THE TOLERANCE. (SEE PAGE 44, EXAMPLE 2-10)

A DATUMS

Locate the projector A Plan View
If we wanted to mount our projector from the ceiling what three dimensions would we need……. and in what order? A Screen Projector Plan View

Locate the projector B Screen Projector Plan View

Locate the projector C Elevation View Mounting Bracket A B C Screen
Floor

A DATUMS DATUMS = ARE PLANES, SURFACES, POINTS, LINES OR AXES FROM WHICH MEASUREMENTS ARE MADE. THEY IDENTIFY SURFACES OR AXES THAT ARE IMPORTANT TO THE FUNCTION OF THE DESIGN.

Datum Planes A

Datum Planes A A

Datum Planes A B A

A C B A

Datum Placement on Drawings
B C DATUM FEATURE SYMBOLS ARE PLACED ON THE EDGE VIEW OR ON EXTENSION LINES. THE ORDER IN WHICH THE DATUM REFERENCE LETTERS ARE PLACED IN THE FEATURE CONTROL FRAME SIGNIFY THEIR IMPORTANCE. THIS IS CALLED THE ORDER OF PRECEDENCE.

Datum Axis Placement on Drawings
.25 B DATUM AXIS

Datum Axis Placement on Drawings
ON THE OUTSIDE SURFACE (THE EDGE) OF A CYLINDRICAL FEATURE. ON THE LEADER LINE SHOULDER THE SYMBOL CAN ALSO BE PLACED ON THE EXTENSION LINE.

Datum Axis Placement on Drawings
THE DATUM SYMBOL CAN ALSO BE ATTACHED TO THE FEATURE CONTROL FRAME.

Datum Target Placement on Drawings
At times only a small area on a surface will be used as a datum. To identify these areas a Datum Target Symbol is used. 12 X DATUM TARGET SYMBOL = ARE USED TO DESIGNATE POINTS OR A SPECIFIC SURFACE AREA. THEY ARE USED WHEN IT MAY NOT BE POSSIBLE TO ESTABLISH AN ENTIRE SURFACE AS A DATUM. (SEE EXAMPLE 3-12 PAGE 71)

12 X

Review Edge view Extension lines Leader line shoulder
1. Define Datum?  Are planes, surfaces, points, lines or axes from which measurements are made. They identify surfaces or axes that are important to the function of the design. 2. Describe the Datum Feature symbol? 3. List three areas where datum symbols should be placed? Edge view Extension lines Leader line shoulder Feature control frame A

Review (cont.) 4. When are Datum Target Symbols used?  They are used to designate points or a specific surface area. They are used when it may not be possible to establish an entire surface as a datum. 5. Describe the Datum Target symbol?

GDT Problems

Problem 1 Solution

L L M

Problem 2 Solution

FORM TOLERANCES

Objectives Identify form tolerance symbols, explain their purpose, and apply them to a drawing. Straightness Flatness Cylindricity Circularity

What are Form Tolerances?
Form Tolerances are applied to single features and, therefore, are not related to a datum. They specify a zone in which the dimensioned feature must be controlled.

STRAIGHTNESS

Straightness a Form Tolerance
A condition where an element of a surface or an axis is in a straight line.

What does this mean? HOLE DIA. By requiring a .04 tolerance zone allowance is made for the imperfection of the rod while stating an acceptable range for it use in the assembly.

FLATNESS

Flatness a Form Tolerance
A condition of a surface where all of the elements are in one plane. The problem is….

….can any surface be made perfectly flat?
So the designer must establish a range or zone of allowable variation. The form tolerance ‘Flatness’ is used to control the amount of variation on a flat surface.

Unlike straightness which controls the form of an object… flatness is used to control only a surface.

CIRCULARITY

Circularity a Form Tolerance
What kind of ride would you get if the wheels on you car were ‘out-of-round’? Is it possible to make a wheel that is perfectly round? How do you control the amount of allowable variation?

Circularity a Form Tolerance
Circularity is established by two concentric circles created by a cross-section thru a rod or the center of a sphere. 0.25 The problem is….

CYLINDRICITY

Cylindricity a Form Tolerance
Cylindricity is established by two concentric cylinders within which the entire surface of the cylinder must lie. 0.25 The problem is….

Cylindricity a Form Tolerance
OUT OF TOLERANCE

ORIENTATION TOLERANCES

Objectives Identify orientation tolerance symbols, explain their purpose, and apply them to a drawing. Parallelism Perpendicularity Angularity

What are Orientation Tolerances?
Orientation Tolerances control the relationship of features to one another. One or more datum features shall be referenced. These Orientation Tolerances are total, meaning that all elements of a related surface or axis fall within the specified tolerance zone.

Parallelism an Orientation Tolerance
Parallelism is a condition of a surface or center plane equidistant from a datum plane or axis. Parallelism an Orientation Tolerance

Parallelism an Orientation Tolerance
NOTICE THAT A DATUM IS REFERENCED A

Perpendicularity is a condition of a surface, center or axis at a right angle (90 degrees) to a datum plane or axis.

PERPENDICULARITY an Orientation Tolerance
.312 A A

PERPENDICULARITY an Orientation Tolerance
.312 A A .312 WIDE TOLERANCE ZONE

ANGULARITY is a condition of a surface, center plane or axis at any specified angle from a datum plane or axis.

Angularity an Orientation Tolerance

LOCATION TOLERANCES

Objectives Identify location tolerance symbols, explain their purpose, and apply them to a drawing. Position Concentricity Symmetry

What are Location Tolerances?
Location tolerances are used for the purpose of locating features from datums. They are also used for establishing coaxiality or symmetry.

Positional Tolerance is used to define a zone in which the center, axis, or center plane of a feature is permitted to vary.

THINK OF THE ARROW AS THE CENTER OR AXIS OF THE DRILL.
CONSIDER THE BULLSEYE ON THE TARGET AS THE ACCEPTABLE TOLERANCE ZONE. ANY HIT WITHIN THAT ZONE IS CONSIDERED TO BE A BULLSEYE.

Positional a Location Tolerance

TRUE POSITION AXIS

WHAT IS THE MEANING OF THE FEATURE CONTROL FRAME SHOWN BELOW?
IT MEANS = THE IDENTIFIED HOLE IS TO BE POSITIONED WITHIN A 0.5 DIAMETER OF ITS TRUE (EXACT) POSITION, AT ITS MAXIMUM MATERIAL CONDITION. THE HOLE WILL BE PERPENDICULAR TO DATUM-A, AND LOCATED FROM DATUM-B AND DATUM-C.

Positional Tolerance Application
B C

Concentricity Tolerance is used to establish a relationship between the axes of two or more cylindrical features of an object. When two or more cylindrical features share the same axis, they are said to be coaxial.

Concentricity a Location Tolerance

Symmetry Tolerance is a center plane relationship of the features of an object establishing a median point to center plane control.

Symmetry a Location Tolerance

GDT Problems A M L

GDT Pin & Ring Problem

GDT Placement Problem 1 Instructions: Ortho sketch, model and detail the Tool Post. Add the required GDT shown below. Top surface is to be a primary datum Top surface to be smooth within .002 Rear surface is to be a secondary datum Right-side surface is to be a tertiary datum .625 Dia hole in top to be positioned within .002 .625 Dia hole in base to parallel to .625 Dia. at top within .002

GDT Placement Problem 2 Instructions: Ortho sketch model and detail the Frame Guide. Add the required GDT shown below. Bottom surface is to be a primary datum Right-side surface is to be a secondary datum Front surface is to be a tertiary datum The two 10 Dia holes in top to be positioned within .01, at maximum material condition The right-side surface is to be at right angles with the base within .02

GDT Placement Problem 3 Instructions: Model and detail the Roller Stud and add the required GDT shown below. Axis of the – Dia is to be a primary datum The – Dia to be on the same center as the – Dia within .01 The – Dia to be straight within .01, at maximum material condition

GDT Placement Problem 4 Instructions: Model and detail the Center Bushing and add the required GDT shown below. Axis of the Dia hole is to be a primary datum Bottom surface is to be a secondary datum Bottom surface is to be flat within .002 1.372 Dia hole is to be 90 degrees to the bottom surface within .005 at LMC. Upper Dia surface to be parallel to the bottom within .005. The three .375 Dia holes are to be positioned within .001 at MMC.