Lecture 2ASASA

7/28/2019 Lecture 2ASASA

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Engineering 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 th is chapter we wi l l

• 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




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Outline

In th is chapter we wi l l

• 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




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Objectives

The object ives of th is 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 theproposed product would look like

Provide information on dimensions and

material used to make the proposed product

Provide views from the top, the side, and thefront




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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 view

Front view

Right-side view




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Orthographic Views

• Three types of lines used in orthographical

views

Sol id l ines represent

• Visible edges of the planes• Intersection of two planes

Hidden or dashed l ines represent

• An edge of a plane

• Extreme limits of a cylindrical hole inside theobject

• Intersection of two planes not visible from the

direction you are looking




Centerl ines represent

• Line of symmetry

• Center of holes

• Center of cylinders

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Orthographic Views




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Orthographic Views

Some objects can be fully described with one viewor two views

Washer can be described

by 1 view and thickness

This object can be

described by 2 views:

front and top




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Example 16.1 – Orthographic Views

Given : object as shown

Find : draw the orthographic views

Solut ion :

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 include

Dimensions

Tolerances Materials from which products will be made

Finished surfaces marked

Other notes such as part numbers




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Dimensioning

• Two concepts when specifying dimensions Size

Location

• Basic dimensioning practice Dimension l ines

• Provide information on the size of the object

Extension l ines

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

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




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Dimensioning

Leaders

• Arrows that point to a circle or a fillet for thepurpose of specifying their sizes

Fil let

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

Inform ation 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 belowFind : show dimensions in the orthographic views

Solut ion :

Orthographic views




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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 thespecified value?

• Must specify a tolerance on your drawing

regarding the machine part dimension For example, 2.50 cm +/- 0.01 cm




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Isometric View

• Isometr ic 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 i l lustrat ions

• Used to show parts or products in parts

manuals, repair manuals, and productcatalogs




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Isometric Drawings – Procedures

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

Step 1

Draw width, height, and depth axes

Step 2

Measure and draw total width, height, and

depth of object




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Step 3Create the front, top, and

side work faces

Step 4

Complete the drawing asmarked by the remaining

line numbers

Original




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Step 5


Step 5Erase unnecessary lines to

yield final drawing

Original




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Example 16.3 – Isometric Drawings

Given : object as shownFind : draw isometric view of object

Solut ion :

Step 1

Draw width, height, and depth axes




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Step 2Measure and draw total width,

height, and depth of object

Step 3

Create the front, top, and

side work faces

Original




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Step 4Complete the drawing

Step 5

Erase unnecessary lines

Original




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Sectional Views

• Sectional views are used when objects

have complex interiors

Reveal the inside of the object

Created by making an imaginary cut throughthe object

The direction of the sight is marked using

directional arrows




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Sectional Views

A sectional view of anobject

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 types

Full 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 rightFind : draw sectional view of object as marked by

the cutting plane

Solut ion :

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 symbols

Convey information

Effectively 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 dimension

Specifying material size Indicating finished surfaces

• You should know when to use isometric

views and finished surfaces

• You should be familiar with the differenttypes of sectional views




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Summary

• You should know why we need and useengineering symbols to communicateamong ourselves

• You should be familiar with some of thecommon civil, electrical, and mechanicalengineering symbols




Engineering Drawing and Symbols

Questions?

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Lecture 2ASASA