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CHAPTER 16Engineering Drawings and Symbols
© 2011 Cengage Learning Engineering. All Rights Reserved.
Chapter 16: Sections 1 – 5
Material to be Covered
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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
© 2011 Cengage Learning Engineering. All Rights Reserved.
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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
© 2011 Cengage Learning Engineering. All Rights Reserved.
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Objectives
The objectives of this chapter are to
• Introduce engineering graphical communication principles
• To discuss why engineering drawings are important
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Importance of Engineering Drawing
• “a picture is worth a thousand words”
• In engineering, a good drawing is worth even more than a thousand words
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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
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Orthographic Views
Orthographic views show what an object’s projection looks like when seen from the top, the front, or the side
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Orthographic Views
Relative locations of the top, bottom, front, back, right-side, and left-side view
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Orthographic Views
• Views needed to fully describe an object Top viewFront viewRight-side view
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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
© 2011 Cengage Learning Engineering. All Rights Reserved.
Centerlines represent• Line of symmetry
• Center of holes
• Center of cylinders
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Orthographic Views
centerline of
cylinder
visual edge
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hidden cylindrical hole
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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
© 2011 Cengage Learning Engineering. All Rights Reserved.
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Example 16.1 – Orthographic Views
Given: object as shown
Find: draw the orthographic views
Solution:
Front view
Top view
Side view
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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
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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
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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
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Dimensioning
dimension line
leader
centerline
extension line
Basics of dimensioning practice
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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
© 2011 Cengage Learning Engineering. All Rights Reserved.
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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.
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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
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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
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Isometric Drawings – Procedures
Step 3Create the front, top, and side work faces
Step 4Complete the drawing as marked by the remaining line numbers
Original
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Step 5
Isometric Drawings – Procedures
Step 5Erase unnecessary lines to yield final drawing
Original
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Example 16.3 – Isometric Drawings
Given: object as shown
Find: draw isometric view of object
Solution:
Step 1Draw width, height, and depth axes
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Example 16.3 – Isometric Drawings
Step 2Measure and draw total width, height, and depth of object
Step 3Create the front, top, and side work faces
Original
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Example 16.3 – Isometric Drawings
Step 4Complete the drawing
Step 5Erase unnecessary lines
Original
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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
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Sectional Views
A sectional view of an object
Identifying letter
on solid section
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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
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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
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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
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Sectional Views – Illustrations
Full sectional view
Half-sectional viewRemoved sectional view
Rotated sectional view
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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
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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
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Examples of Engineering Symbols
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Examples of Engineering Symbols
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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.
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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
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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.
Engineering Drawing and Symbols
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