16-1 CHAPTER 16 Engineering Drawings and Symbols © 2011 Cengage Learning Engineering. All Rights Reserved

16-1

CHAPTER 16Engineering Drawings and Symbols

© 2011 Cengage Learning Engineering. All Rights Reserved.

Chapter 16: Sections 1 – 5

Material to be Covered

16-3

Outline

In this chapter we will

• Discuss the need for conventional engineering symbols and drawings

• Show how vital information for an object is communicated to others using

Orthographic viewsIsometric viewsSectional views


16-4

Outline

In this chapter we will

• Introduce basic rules of an engineering drawing

Showing dimensionsSpecifying material sizeIndicating finished surfaces

• Show some common symbols used in civil, electrical, and mechanical engineering


16-5

Objectives

The objectives of this chapter are to

• Introduce engineering graphical communication principles

• To discuss why engineering drawings are important


16-6

Importance of Engineering Drawing

• “a picture is worth a thousand words”

• In engineering, a good drawing is worth even more than a thousand words


16-7

Importance of Engineering Drawing

• Engineering drawings are important in conveying useful information to other engineers and machinists

Allow the readers to visualize what the proposed product would look like

Provide information on dimensions and material used to make the proposed product

Provide views from the top, the side, and the front


16-8

Orthographic Views

Orthographic views show what an object’s projection looks like when seen from the top, the front, or the side


16-9

Orthographic Views

Relative locations of the top, bottom, front, back, right-side, and left-side view


16-10

Orthographic Views

• Views needed to fully describe an object Top viewFront viewRight-side view


16-11

Orthographic Views

• Three types of lines used in orthographical views

Solid lines represent• Visible edges of the planes

• Intersection of two planesHidden or dashed lines represent

• An edge of a plane

• Extreme limits of a cylindrical hole inside the object

• Intersection of two planes not visible from the direction you are looking


Centerlines represent• Line of symmetry

• Center of holes

• Center of cylinders

16-12

Orthographic Views

centerline of

cylinder

visual edge


hidden cylindrical hole

16-13

Orthographic Views

Some objects can be fully described with one view or two views

Washer can be described by 1 view and thickness

This object can be described by 2 views: front and top


16-14

Example 16.1 – Orthographic Views

Given: object as shown

Find: draw the orthographic views

Solution:

Front view

Top view

Side view


16-15

Dimensioning and Tolerancing

• American National Standard Institute (ANSI) sets the standards for the dimensioning and tolerancing practice for engineering drawings

• Every engineering drawing must includeDimensionsTolerancesMaterials from which products will be madeFinished surfaces markedOther notes such as part numbers


16-16

Dimensioning

• Two concepts when specifying dimensionsSizeLocation

• Basic dimensioning practiceDimension lines

• Provide information on the size of the objectExtension lines

• Lines that extend from the points to which the dimension or location is to be specified

• Lines are drawn parallel to each other with dimension line placed between them


16-17

Dimensioning

Leaders• Arrows that point to a circle or a fillet for the

purpose of specifying their sizesFillet

• Rounded edges of an object• Size, radius of roundness must be specified

Information box contains• Name of person who prepared the drawing• Title of the drawing• Date• Scale• Sheet number and drawing number


16-18

Dimensioning

dimension line

leader

centerline

extension line

Basics of dimensioning practice


16-19

1”

Side viewFront view

Top view

Example 16.2 – Dimensioning

Given: an object and its dimensions are shown below

Find: show dimensions in the orthographic views

Solution:

Orthographic views


16-20

Tolerancing

• Engineered products generally consist of many parts

Would everything fit correctly if the actual dimension of machine part is off from the specified value?

• Must specify a tolerance on your drawing regarding the machine part dimension

For example, 2.50 cm +/- 0.01 cm


16-21

Isometric View

• Isometric drawing shows the 3-dimensions of an object in a single view

Use to visualize objects that are difficult to visualize in their orthographic views

• Also called technical illustrations

• Used to show parts or products in parts manuals, repair manuals, and product catalogs


16-22

Isometric Drawings – Procedures

We will use the object shown to illustrate the steps of isometric drawings

Step 1Draw width, height, and depth axes

Step 2Measure and draw total width, height, and depth of object


16-23


Step 3Create the front, top, and side work faces

Step 4Complete the drawing as marked by the remaining line numbers

Original


16-24

Step 5


Step 5Erase unnecessary lines to yield final drawing

Original


16-25

Example 16.3 – Isometric Drawings

Given: object as shown

Find: draw isometric view of object

Solution:

Step 1Draw width, height, and depth axes


16-26


Step 2Measure and draw total width, height, and depth of object

Step 3Create the front, top, and side work faces

Original


16-27


Step 4Complete the drawing

Step 5Erase unnecessary lines

Original


16-28

Sectional Views

• Sectional views are used when objects have complex interiors

Reveal the inside of the objectCreated by making an imaginary cut through

the objectThe direction of the sight is marked using

directional arrows


16-29

Sectional Views

A sectional view of an object

Identifying letter

on solid section


16-30

Sectional Views

• Based on how complex the inside of an object is, different methods are used to show sectional views

• Common section typesFull section views

• Created when the cutting plane passes through the object completely


16-31

Sectional Views

Half-sectional views• Used for symmetrical objects

• Draw half of the object in sectional view

• Draw the other half of the object as exterior view

• Can show interior and exterior views of an object using one view

Rotated section views• Used when the object has a uniform cross

section with a shape that is difficult to visualize

• Section is rotated 90o and is shown in the plane of view


16-32

Sectional Views

Removed sections• Similar to rotated section

• Rotated section views are removed from the view itself and shown adjacent to the view

• Used for objects with a variable cross section

• Generally many cuts through the section are shown


16-33

Sectional Views – Illustrations

Full sectional view

Half-sectional viewRemoved sectional view

Rotated sectional view


16-34

Example 16.4 – Sectional Views

Given: object as shown on the right

Find: draw sectional view of object as marked by the cutting plane

Solution:

Solid material

Sectional view

Original


16-35

Engineering symbols

• Why do we need engineering symbols?Symbols are “language” used by engineers to

convey• Their ideas

• Their solutions to problems

• Their analyses of certain situations

• Conventional engineering symbolsConvey informationEffectively communicate to other engineers


16-36

Examples of Engineering Symbols


16-37

Examples of Engineering Symbols


16-38

Summary

• You should have a good understanding of the importance of engineering drawings in conveying information to other engineers, machinists, and assembly personnel

• You should understand what is meant by orthographic views, isometric drawing, and sectional views.


16-39

Summary

• You should understand basic rules for an engineering drawing

Showing dimensionSpecifying material sizeIndicating finished surfaces

• You should know when to use isometric views and finished surfaces

• You should be familiar with the different types of sectional views


16-40

Summary

• You should know why we need and use engineering symbols to communicate among ourselves

• You should be familiar with some of the common civil, electrical, and mechanical engineering symbols


Engineering Drawing and Symbols

Questions?

Documents

16-1 CHAPTER 16 Engineering Drawings and Symbols © 2011 Cengage Learning Engineering. All Rights Reserved