1. Geometric Dimensioning and Tolerancing
Engineering
Drawing and Design
Seventh Edition
Chapter 16
Geometric Dimensioning and Tolerancing

2. GD&T stands for Geometric Dimensioning & Tolerancing
DIMENSION is a geometric characteristic the size of which is specified such as length,angle,location,or center distance
TOLERANCE on a dimension is the total permissible variation in its size, which is equal to the difference between the limits of size.

3. GEOMETRIC DIMENSIONING
AND TOLERANCING
DIMENSIONS OF A PART

4. GEOMETRIC DIMENSIONING
AND TOLERANCING
TOLERANCE SIZES

5. GEOMETRIC DIMENSIONING
AND TOLERANCING
TYPE OF TOLERANCE

6. GEOMETRIC DIMENSIONING
AND TOLERANCING
SIZES OF MATING PARTS

7. Deviations
The difference between the basic size and the maximum and minimum sizes are called the UPPER & LOWER deviations.
The BASIC DIMENSION represents the theoretical exact size or location of a feature.

8. GEOMETRIC DIMENSIONING
AND TOLERANCING
DEVIATIONS

9. GEOMETRIC DIMENSIONING
AND TOLERANCING
BASIC (EXACT) DIMENSIONS
Are shown in a rectangle to indicate that the tolerances in the general tolerance note do not apply

10. Datum
A DATUM is a theoretical exact feature from which dimensions may be taken.
A DATUM is generally chosen as an edge or feature which has the greatest influence in a specific measurement.

11. GEOMETRIC DIMENSIONING
AND TOLERANCING
EXAMPLES OF DEVIATION OF FORM WHEN PERFECT FORM AT THE MAXIMUM MATERIAL CONDITION IS REQUIRED

12. GEOMETRIC DIMENSIONING
AND TOLERANCING
EXAMPLES OF DEVIATION OF FORM WHEN PERFECT FORM AT THE MAXIMUM MATERIAL CONDITION IS REQUIRED

13. Geometric Tolerance
A geometric tolerance is the maximum permissible variation of form, profile, orientation, location, and runout from that indicated or specified on a drawing.
Feature control frame for an individual feature is divided into compartments containing, at the least, the geometric tolerance symbol and the geometric tolerance value

14. Feature control frame (fig.16-16)
Geometric characteristic symbol
Geometric tolerance
Datums (if used)
Modifiers as required (*MMC for example)

15. GEOMETRIC DIMENSIONING
AND TOLERANCING
16-2
16-5
STRAIGHTNESS
FORM
INDIVIDUAL
FEATURES
SEE UNIT
SYMBOL
CHARACTERISTIC
TYPE OF
TOLERANCE
FEATURE
GEOMETRIC CHARACTERISTIC SYMBOLS

16. GEOMETRIC DIMENSIONING
AND TOLERANCING
16-4
MAXIMUM
MATERIAL
CONDITION
SUPPLEMENTARY
SYMBOLS
SEE UNIT
SYMBOL
CHARACTERISTIC
TYPE OF
TOLERANCE
FEATURE
GEOMETRIC CHARACTERISTIC SYMBOLS

17. GEOMETRIC DIMENSIONING
AND TOLERANCING
16-4
LEAST
MATERIAL
CONDITION
SUPPLEMENTARY
SYMBOLS
SEE UNIT
SYMBOL
CHARACTERISTIC
TYPE OF
TOLERANCE
FEATURE
GEOMETRIC CHARACTERISTIC SYMBOLS

18. GEOMETRIC DIMENSIONING
AND TOLERANCING
16-9
PROJECTED TOLERANCE
ZONE
SUPPLEMENTARY
SYMBOLS
SEE UNIT
SYMBOL
CHARACTERISTIC
TYPE OF
TOLERANCE
FEATURE
GEOMETRIC CHARACTERISTIC SYMBOLS

19. GEOMETRIC DIMENSIONING
AND TOLERANCING
16-9
16-11
BASIC DIMENSION
SUPPLEMENTARY
SYMBOLS
SEE UNIT
SYMBOL
CHARACTERISTIC
TYPE OF
TOLERANCE
FEATURE
GEOMETRIC CHARACTERISTIC SYMBOLS

20. GEOMETRIC DIMENSIONING
AND TOLERANCING
16-6
DATUM
FEATURE
SUPPLEMENTARY
SYMBOLS
SEE UNIT
SYMBOL
CHARACTERISTIC
TYPE OF
TOLERANCE
GEOMETRIC CHARACTERISTIC SYMBOLS

21. GEOMETRIC DIMENSIONING
AND TOLERANCING
16-11
DATUM
TARGET
SUPPLEMENTARY
SYMBOLS
SEE UNIT
SYMBOL
CHARACTERISTIC
TYPE OF
TOLERANCE
FEATURE
GEOMETRIC CHARACTERISTIC SYMBOLS

22. Form Tolerances
FORM TOLERANCES control the straightness, flatness, circularity and cylindricity
Form tolerances apply to individual features and as such do not require locating dimensions.
ORIENTATION TOLERANCES control angularity, parallelism, and perpendicularity

23. More on FORM TOLERANCES
Straightness-a condition in which the element of a surface or a median line is a straight line
Flatness of a surface is a condition in which all surface elements are in one plane

24. GEOMETRIC DIMENSIONING
AND TOLERANCING
FEATURE CONTROL FRAME

25. GEOMETRIC DIMENSIONING
AND TOLERANCING
ATTACHED USING
A LEADER
APPLICATION OF FEATURE CONTROL FRAME

26. MMC, RFS, LMC applies to features subject to variations in size
MMC (Maximum Material Condition) is when a feature or part is at the limit of size, which results in its containing the maximum amount of material.
LMC (Least Material Conditon) refers to the size of a feature that results in the part containing the minimum amount of material. Thus it is the minimum limit of size for an external feature.
RFS (Regardless of feature size) indicates that a geometric tolerance applies to any size of a feature that lies within its size tolerance.

27. Datums and the 3-plane concept (16-5)
Datum is a theoretical point, line, plane, or other geometric surface fromwhich dimensions are measured when so specified or to which geometric tolerances are referenced
Datum feature is a feature of a part, such as a surface, that forms the basis for a datum or is used to establish its location

28. 3-plane system
The three planes constitue a datum system from which measurements can be taken. They will appear on the drawing.
Datum feature symbol is used on the drawing to identify these surfaces

29. GEOMETRIC DIMENSIONING
AND TOLERANCING
THE DATUM PLANES

30. GEOMETRIC DIMENSIONING
AND TOLERANCING
THE DATUM PLANES

31. GEOMETRIC DIMENSIONING
AND TOLERANCING
THE DATUM PLANES

32. Orientation tolerancing (16-6)
Angularity, parallelism and perpendicularity are orientation tolerances applicable to related features
Angularity is the condition of a surface or axis at a specified angle (other than 90⁰or 0⁰) from a datum plane or axis
Perpendicularity is the condition of a surface at 90⁰ to a datum plane or axis. *A perpendicularity tolerance for a flat surface specifies a tolerance zone defined by two parallel planes perpendicular to a datum plane or axis
Parallelism is the condition of a surface equidistant at all points from a datum plane. Parallelism for a flat surface specifies a tolerance zone defined by two planes or lines parallel to a datum plane or axis.

33. Datum Targets (16-11)
Datum target symbols are used to locate specific reference positions to be used on large datum surfaces*
the surface of a feature may be so large that a gage designed to make contact with the full surface may be too expensive or cumbersome to use
Functional requirements of the part may necessitate the use of only a portion of a surface as a datum feature

34. CAD APPLICATIONS
TOLERANCE DIALOG BOX

35. CAD APPLICATIONS
TOLERANCE SYMBOL DIALOG BOX