# eas 3711 dimensioning and tolerancing

Embed Size (px)

DESCRIPTION

TRANSCRIPT

- 1. Dimensioning & Tolerancing

Dr. Fairuz I. Romli

Semester 2 2009/2010

2. Introduction: Dimensioning

Working drawings must show dimensions and contain notes conveying
sizes, specifications and other information

Techniques of dimensioning presented are based primarily on the
standards of the American National Standards Institute (ANSI)

Two commonly used units of measurement

Metric units in millimeter round the millimeters to the nearest
whole number

English units in inches

always show up to two decimal

places, even for whole numbers

Earle, J. H. Graphics for Engineers, Addison-Wesley Publishing,
1996

3. Dual Dimensioning

On some drawings, both metric and English units might be
required

Place the millimeter equivalent either under or over the inch
units

Place the converted dimension in brackets to the right of the
original dimension

Be consistent in the arrangement throughout the whole drawing

Earle, J. H. Graphics for Engineers, Addison-Wesley Publishing,
1996

4. Metric Designation

In metric system (SI)

First-angle projection positions the front view over the top view
and the right-side view to the left of the front view

American system use third-angle projection places top view over the
front view

Label metric drawings with one of the symbols

Earle, J. H. Graphics for Engineers, Addison-Wesley Publishing,
1996

5. Numeric & Symbolic Dimensioning

Vertical dimensions aligned or uni-directional

Uni-directional all dimensions appear in the standard horizontal
position

Aligned numerals are parallel with vertical and angular dimension
lines and read from the right-hand side of the drawing, never from
the left-hand side

Earle, J. H. Graphics for Engineers, Addison-Wesley Publishing,
1996

6. Numeric & Symbolic Dimensioning

Placement

Dimensions should be placed on the most descriptive views of the
part being dimensioned

First row of dimensions should be at least 3 times the letter
height (3H) from the object

Successive rows of dimensions should be spaced equally at least 2
times the letter height (2H)

Regardless of space limitations numerals have to be the same size
throughout the entire drawing

Earle, J. H. Graphics for Engineers, Addison-Wesley Publishing,
1996

7. Numeric & Symbolic Dimensioning

Earle, J. H. Graphics for Engineers, Addison-Wesley Publishing,
1996

8. Numeric & Symbolic Dimensioning

Symbols

To save some drawing times use these symbols instead of words

Size usually based on the letter height often 1/8 inch

Earle, J. H. Graphics for Engineers, Addison-Wesley Publishing,
1996

9. Dimensioning Rules

To place dimensions and notes on drawings most effectively

However, from time to time, rules of dimensioning must be violated
due to the complexity of the part or shortage of space

Rules for prisms

Place the first row of dimensions at least 3H from the object

Successive rows at least 2H from each other

Earle, J. H. Graphics for Engineers, Addison-Wesley Publishing,
1996

10. Dimensioning Rules

Rules for prisms

Place the dimensions between the views sharing these
dimensions

Earle, J. H. Graphics for Engineers, Addison-Wesley Publishing,
1996

11. Dimensioning Rules

Rules for prisms

Place the dimensions on the most descriptive views of an
object

Earle, J. H. Graphics for Engineers, Addison-Wesley Publishing,
1996

12. Dimensioning Rules

Rules for prisms

Dimension visible features, not hidden features

Earle, J. H. Graphics for Engineers, Addison-Wesley Publishing,
1996

13. Dimensioning Rules

Rules for prisms

Leave the last dimension blank in a chain of dimensions when you
also give an overall dimension

Earle, J. H. Graphics for Engineers, Addison-Wesley Publishing,
1996

14. Dimensioning Rules

Rules for prisms

Place dimensions in well-organized lines for uncluttered
drawings

Earle, J. H. Graphics for Engineers, Addison-Wesley Publishing,
1996

15. Dimensioning Rules

Rules for prisms

Do not duplicate dimensions on a drawing to avoid errors or
confusion

Earle, J. H. Graphics for Engineers, Addison-Wesley Publishing,
1996

16. Dimensioning Rules

Rules for prisms

Dimension lines should cross any other lines unless absolutely
necessary

Earle, J. H. Graphics for Engineers, Addison-Wesley Publishing,
1996

17. Dimensioning Rules

Rules for prisms

Extension lines may cross other extension lines or object if
necessary

Earle, J. H. Graphics for Engineers, Addison-Wesley Publishing,
1996

18. Dimensioning Rules

Rules for prisms

Leave a small gap from the edges of an object to extension lines
that extend from them. Do not leave gaps where extension lines
cross object lines or other extension lines

Earle, J. H. Graphics for Engineers, Addison-Wesley Publishing,
1996

19. Dimensioning Rules

Rules for prisms

Earle, J. H. Graphics for Engineers, Addison-Wesley Publishing,
1996

20. Dimensioning Rules

Rules for angles

Place angular dimensions outside angular notches by using extension
lines

Earle, J. H. Graphics for Engineers, Addison-Wesley Publishing,
1996

21. Dimensioning Rules

Rules for angles

Dimension a bent surface rounded corner by locating its theoretical
point of intersection with extension lines

Earle, J. H. Graphics for Engineers, Addison-Wesley Publishing,
1996

22. Dimensioning Rules

Rules for cylindrical parts and Holes

Dimension the diameter (not the radius) of a cylinder in the
rectangular view

Earle, J. H. Graphics for Engineers, Addison-Wesley Publishing,
1996

23. Dimensioning Rules

Rules for cylindrical parts and Holes

Dimensions on concentric cylinders are easier to read if they are
staggered within their dimension lines

Earle, J. H. Graphics for Engineers, Addison-Wesley Publishing,
1996

24. Dimensioning Rules

Rules for cylindrical parts and Holes

Dimension holes in their circular view with leaders whenever
possible, but dimension them in their rectangular views if
necessary

Earle, J. H. Graphics for Engineers, Addison-Wesley Publishing,
1996

25. Dimensioning Rules

Rules for cylindrical parts and Holes

Draw leaders pointing toward the centers of holes

Earle, J. H. Graphics for Engineers, Addison-Wesley Publishing,
1996

26. Dimensioning Rules

Rule for leaders

Extend leaders from the first or the last word of a note with a
horizontal elbow

Earle, J. H. Graphics for Engineers, Addison-Wesley Publishing,
1996

27. Dimensioning Rules

Rule for arcs and radii

When space permits, place dimensions and arrows between the center
and the arc

When space is not available for the numbers, place the arrow
between the center and the arc number outside

If there is no space for the arrow inside, place both the dimension
and arrow outside the arc with a leader

Earle, J. H. Graphics for Engineers, Addison-Wesley Publishing,
1996

28. Dimensioning Rules

Rule for location dimensions

Locate cylindrical holes in their circular views by coordinates to
their centers

Earle, J. H. Graphics for Engineers, Addison-Wesley Publishing,
1996

29. Introduction: Tolerancing

Technique of dimensioning parts within a required range of
variation

Each dimension is allowed a certain degree of variation within a
specified zone

A tolerance should be as large as possible without interfering with
the function of the part to minimize production costs

Manufacturing costs increase as tolerances become smaller

Positioning of tolerances

Earle, J. H. Graphics for Engineers, Addison-Wesley Publishing,
1996

30. Rules of Tolerancing

Order of numbers

Place upper limits either above or to the right of lower
limits

In plus minus tolerancing, place the plus limits above the minus
limits

Earle, J. H. Graphics for Engineers, Addison-Wesley Publishing,
1996

31. Rules of Tolerancing

Positioning of numbers

Spacing and ratios of numerals used to specify tolerances on
dimensions

Earle, J. H. Graphics for Engineers, Addison-Wesley Publishing,
1996

32. Q1

33. Q1

34. Q1

35. Q2

36. Q2

37. Q2