1. Engineering Drawing and Design Chapter 8 Basic Dimensioning
Sixth Edition
Chapter 8
Basic Dimensioning

2. Chapter 8 Basic
Dimensioning
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3. 8-1 Basic Dimensioning Using dimensioning in engineering drawings
Basic rules for dimensioning
Units of measurement
Unidirectional and aligned systems of dimensioning
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4. Working Drawing
Definition: A drawing from which a part can be produced.
Must be a complete set of instructions
Consists of:
The views needed to describe the shape
Dimensions needed for manufacture
Specifications (materials, etc.)

5. Dimensions are noted using:
Extension lines
Dimension lines
Leader s
Notes
Symbols

6. Basic Rules for Dimensioning
1. Place dimensions between views when possible.
2. Place the dimension line for the shortest length, width, or height nearest the outline of the object. Parallel dimension lines are placed in order of their size, making the longest dimension line the outermost.
3. Place dimensions with the view that best shows the characteristic contour or shape of the object. When this rule is applied, dimensions will not always be between views.
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7. Basic Rules for Dimensioning
4. On large views, dimensions can be placed on the view to improve clarity.
5. Use only one system of dimensions, either unidirectional or aligned, on any one drawing.
6. Dimensions should not be duplicated in other views.
7. Dimensions should be selected so that it will not be necessary to add or subtract dimensions in order to define or locate a feature.
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8. ?
Quick Quiz
What dimensioning rule allows dimensions not to be placed between views?
Place dimensions with the view that best shows the characteristic contour or shape of the object.

9. 8-2 Dimensioning Circular Features
Diameters and radii
Cylindrical and slotted holes

10. Dimensioning Common Features
8-3
Dimensioning Common Features
Chamfers, slopes, tapers,
knurls, &
undercuts
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11. Repetitive features
Dimensioned once with an indication of how many repetitions are required

12. Chamfers
Normally dimensioned using angle and linear length

13. Slopes
Expressed as a ratio of difference in heights at a specified distance apart

14. Tapers
Expressed as the ratio of the difference in sections

15. Knurls
Expressed in terms of type, pitch, and diameter before and after knurling

16. Undercuts
Expressed as width by diameter
Plain Undercut

17. Quick Quiz ? How is a slope dimensioned?
As a ratio of difference in heights at a specified distance apart

18. 8-4 Dimensioning Methods Rectangular coordinate dimensioning
Polar coordinate, chordal, true- position, chain, and datum dimensioning
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19. Rectangular Coordinate Dimensioning
Indicates distance, location, and size
Uses linear dimensions measured
parallel or perpendicular to reference axes
datum planes that are parallel or perpendicular to each other.

20. Polar Coordinate Dimensioning
Commonly used in circular planes or circular configurations of features.
Indicates the position of a point, line, or surface with a linear dimension and an angle.

21. Chordal Coordinate Dimensioning
May be used for the spacing of points on the circumference of a circle relative to a datum.

22. True-Position Coordinate Dimensioning
Covered more completely in chapter 16.

23. Chain Dimensioning
A series of dimensions is applied on a point-to-point basis.
Chain dimensioning may allow undesirable tolerance accumulation.

24. Datum or Common-Point Dimensioning
Several dimensions are measured from a common point or line.

25. ?
Quick Quiz
Which kind of dimensioning is a series of dimensions applied on a point-to- point basis?
Chain dimensioning

26. 8-5 Limits and Tolerances
Permissible variations in form, size, or location
Tolerancing methods
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27. Limit Dimensioning
High limit is placed above the low limit

28. Plus-and-Minus Tolerancing
Bilateral:
Variation is allowed in both directions
Unilateral
Variation is only allowed in one direction

29. Definition: Tolerance Accumulation
The effect of cumulative tolerances caused by the relationship of tolerances to each other.
Chain dimensioning is the method that allows the most accumulation of tolerances.
Direct dimensioning allows for the least tolerance accumulation.

30. 8-6 Fits and Allowances Interchangeability of parts Standard inch fits
Preferred metric limits and fits

31. Fit Types Clearance fit Interference fit Transition fit
A fit between mating parts that leaves space between them
Interference fit
A fit between mating parts in which the parts interfere with each other
Transition fit
A fit in which the limits of size overlap, so that the resulting parts may have either a clearance or an interference
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32. Quick Quiz ? What term refers to the cumulative effect of tolerances?
Tolerance accumulation

33. Interchangeability of Parts
Completely interchangeable assembly
All mating parts are toleranced to assemble and function without machining or fitting
Fitted assembly
Mating features are made to relate to each other. Individual members of mating features are not interchangeable
Selected assembly
All parts are mass-produced, but members of mating features are selected so they will have the required relationship with each other.

34. Further Study
Various systems of limits and fits are outlined on pages of the Engineering Drawing and Design textbook.

35. 8-7 Surface Texture Surface texture characteristics
Representing surface texture on a drawing
Application
Machined surfaces
Janis Christie

36. Surface Texture Characteristics
Roughness
The finer irregularities in surface texture
Roughness-height value
The arithmetic average deviation expressed in microinches or micrometers measured normal to the center line.

37. Surface Texture Characteristics
Roughness spacing
The distance parallel to the nominal surface between the successive peaks of the predominant roughness pattern

38. Surface Texture Characteristics
Lay
The direction of the predominant surface pattern
Flaws
Irregularities that occur infrequently, including defects.

39. Machining symbols Machining symbol Material removal allowance
Amount of material to be removed is shown to the left of the machining symbol
Material removal prohibited