CHAPTER 16
Engineering Drawings and Symbols
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-1
Material to be Covered
Chapter 16: Sections 1 – 5
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 views
Isometric views
Sectional views
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-3
Outline
In this chapter we will
• Introduce basic rules of an engineering
drawing



Showing dimensions
Specifying material size
Indicating finished surfaces
• Show some common symbols used in civil,
electrical, and mechanical engineering
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-4
Objectives
The objectives of this chapter are to
• Introduce engineering graphical
communication principles
• To discuss why engineering drawings are
important
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-5
Importance of Engineering Drawing
• “a picture is worth a thousand words”
• In engineering, a good drawing is worth
even more than a thousand words
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-6
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
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-7
Orthographic Views
Orthographic views
show what an object’s
projection looks like
when seen from the top,
the front, or the side
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-8
Orthographic Views
Relative locations of the top, bottom, front, back,
right-side, and left-side view
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-9
Orthographic Views
• Views needed to fully describe an object



Top view
Front view
Right-side view
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-10
Orthographic Views
• Three types of lines used in orthographical
views


Solid lines represent
• Visible edges of the planes
• Intersection of two planes
Hidden 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
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-11
Orthographic Views

Centerlines represent
• Line of symmetry
• Center of holes
• Center of cylinders
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-12
Orthographic Views
Some objects can be fully described with one view
or two views
Washer can be described
by 1 view and thickness
© 2011 Cengage Learning Engineering. All Rights Reserved.
This object can be
described by 2 views:
front and top
16-13
Example 16.1 – Orthographic Views
Given: object as shown
Find: draw the orthographic views
Solution:
Top view
Front view
Side
view
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-14
Dimensioning and Tolerancing
• American National Standard Institute
(ANSI) sets the standards for the
dimensioning and tolerancing practice for
engineering drawings
• Every engineering drawing must include





Dimensions
Tolerances
Materials from which products will be made
Finished surfaces marked
Other notes such as part numbers
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-15
Dimensioning
• Two concepts when specifying dimensions


Size
Location
• Basic dimensioning practice


Dimension lines
• Provide information on the size of the object
Extension 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
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-16
Dimensioning

Leaders
• Arrows that point to a circle or a fillet for the
purpose of specifying their sizes


Fillet
• 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
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-17
Dimensioning
leader
centerline
extension line
dimension line
Basics of dimensioning practice
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-18
Example 16.2 – Dimensioning
Given: an object and its dimensions are shown below
Find: show dimensions in the orthographic views
Solution:
Top view
1”
Front view
Orthographic views
Side
view
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-19
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
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-20
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
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-21
Isometric Drawings – Procedures
We will use the object shown to illustrate the
steps of isometric drawings
Step 1
Draw width, height, and depth axes
Step 2
Measure and draw total width, height, and
depth of object
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-22
Isometric Drawings – Procedures
Step 3
Create the front, top, and
side work faces
Step 4
Complete the drawing as
marked by the remaining
line numbers
© 2011 Cengage Learning Engineering. All Rights Reserved.
Original
16-23
Isometric Drawings – Procedures
Step 5
Erase unnecessary lines to
yield final drawing
Step 5
Original
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-24
Example 16.3 – Isometric Drawings
Given: object as shown
Find: draw isometric view of object
Solution:
Step 1
Draw width, height, and depth axes
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-25
Example 16.3 – Isometric Drawings
Step 2
Measure and draw total width,
height, and depth of object
Original
Step 3
Create the front, top, and
side work faces
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-26
Example 16.3 – Isometric Drawings
Step 4
Complete the drawing
Original
Step 5
Erase unnecessary lines
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-27
Sectional Views
• Sectional views are used when objects
have complex interiors



Reveal the inside of the object
Created by making an imaginary cut through
the object
The direction of the sight is marked using
directional arrows
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-28
Sectional Views
A sectional view of an
object
Identifying letter
on solid section
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-29
Sectional Views
• Based on how complex the inside of an
object is, different methods are used to
show sectional views
• Common section types

Full section views
• Created when the cutting plane passes
through the object completely
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-30
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
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-31
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
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-32
Sectional Views – Illustrations
Rotated sectional
view
Full sectional view
Half-sectional view
© 2011 Cengage Learning Engineering. All Rights Reserved.
Removed sectional
view
16-33
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
Original
Sectional view
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-34
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 symbols


Convey information
Effectively communicate to other engineers
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-35
Examples of Engineering Symbols
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-36
Examples of Engineering Symbols
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-37
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.
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-38
Summary
• You should understand basic rules for an
engineering drawing



Showing dimension
Specifying material size
Indicating finished surfaces
• You should know when to use isometric
views and finished surfaces
• You should be familiar with the different
types of sectional views
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-39
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
© 2011 Cengage Learning Engineering. All Rights Reserved.
16-40
Engineering Drawing and Symbols
Questions?