Engineering Graphics(FST ANGLE).PPT

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Orthographic Projection Table of Contents Master Table of ContentsReturn to the Previous Slide Slide 1 QuitGlossary

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57.6

56.6

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41.3

41.1

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B

M42 X 1.5 - 6g

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6.1

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9.4

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Orthographic

Projection

UnitEngineering Graphics

Principles

Copyright 2002

Brigham Young University

All Rights Reserved
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p


Foreword

Orthographic projection (sometimes referred to as multi-viewprojection), is a geometricprocedure used in the engineering disciplines to project multiple graphic images of three-

dimensional objects, onto a single two-dimensional plane. The procedure is also calledengineering drawingor drafting, and is the primary means of communication used bydesigners and engineers in the design process. Multiple views in an orthogonal orientation(each rotated 90 from the other), is fundamental to the definition of feature and partcharacteristicssuch as size, location, orientation, and functional relationships.

In its simplest form, orthographic projection provides a range of six orthographic-specificviews of an object. In your mind, imagine a physical stationary object that has beensuspended in the center of a glass cube. Each of the six sides of the box represents aviewingorprojectionplane. The orientation of the observers line of sight must alwaysbeperpendicular or normalto the planes on the glass box, and the sides of the box must alsobe perpendicular to their adjacent sides. That being the case, the object could onlybeviewed from the front, top, right side, left side, back, or bottom. With the images indelibly

fixed on the planes, and the box unfolded, the projected images or viewswould always beoriented orthographically, and aligned with each other, from view to view on the drawing.

The process of orthographically projecting parts and/or feature characteristics is notnecessarily complicated, but it is complex. It is essential to the delineation of featuregeometry as an aide to the manufacturing process. This unit will give you practice usingthese principles, and will increase your ability to understand and visualize the process.


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How to Proceed

In order to produce mechanical parts, detailed design information must be provided to the

craftsmaninformation that defines and describes relevant geometry and relationships of

descriptive elements on the part. Graphic images or views, developed from specific

orientations, are major elements in this communication process. A primary objective of thisunit is to acquaint you with the process of generating multiple (albeit, geometrically related)

views of mechanical components. The basic theory, rationale, and production techniques

are presented in a systematic order. It is anticipated that you will complete this unit in one

or possibly two sessions (more time and practice may be required if you are new to the

science of engineering graphics).

Begin with a thoughtful preview of the unit objectives, and carefully consider the related

vocabulary words and terminology. As each topic is considered, keep in mind an overall

objective of being able to read an engineering drawing, or to construct correctly projected

views that would be required to describe part features, thus facilitating the manufacturing

process.

Follow each explanation, and practice each technique as outlined for solving orthographic

projection problems. Review concepts that seem unclear, and do each of the exercises that

are providedespecially the self assessment exercises at the end of the presentation. As

you complete the exercises, carefully compare your own sketched solutions with the those

provided, and review the governing principles where necessary.


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Unit Objectives

When you have completed this unit, you will be able to:

Explain the principles upon which orthographic projection is based.

Recognize and identify horizontal, frontal, and profile planes in engineering drawings, and explain

their relationships to standard planes of projection.

Identify the six principal views which may be generated, using the concept of the viewing cube, and

explain their specific orientation and relationships to each other.

Identify normal, inclined, and oblique planes relative to the six principal projection planes.

Read an engineering drawing, and explain the necessity for creating multiple views.

Use graphic tools such as reference planes and fold lines to solve orthographic projection problems.

Apply standard line and view conventions on an engineering drawing.

Solve orthographic problems using at least two techniques of locating and applying data.

Explain and illustrate the differences between first- and third-angle projection.

Demonstrate the appropriate applications for center lines and hidden lines in multi-view drawings.


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Orthographic Projection -- Theory and Practice

Terminology / Vocabulary

Orthographic Projection Theory (Third Angle Projection)

Glass Box Theory

Orientation of Object Features in Orthographic ProjectionDirections and Orientation in Orthographic Projection

Orthographic Projection Principles Review

Orthographic Projection Theory (First Angle Projection)

Multi-view Projection Techniques

Miter Line (1)

Miter Line (2)

Miter Line (3)

Miter Line (4)Solid Example Problem

Compass Projection Technique

Projection Orientation -- View Selection

Pictorial Visualization

Measure and Transfer Method (1)


Measure and Transfer Method (3)Measure and Transfer Method (4)

Pictorial Visualization (Pyramid4a)


An Alternative Solution (5a)

Inclined Surfaces in Orthographic Projection

Oblique Surfaces in Orthographic Projection

Additional Examples (Practice Problems in Orthographic Projection)

Concept Mastery Examination (Self Evaluation)

Orthographic Projection Table of Contents

Table of ContentsTopics:

To assist you in your study of the contents of

this presentation, a Table of Contentshas

been prepared. The topics listed are linked

to the specific content by topic. When

selected with the mouse (in show mode), the

presentation materials will open at the

requested location. The navigation bar at the

bottom of the screen allows you to return tothis slide at any time. Similar tables have

been included in all of the presentations that

follow.


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Orthographic Projection

Station Pointany location in 3-dimensional space that is infinitely displaced from the

object being viewed.Line of Sight(LOS)the orientation of an observer relative to a specific object.

Projection Plane(also called a Viewing PlaneorPicture Plane)the plane onto which

the image of an object is projected.

Visual Raysan infinite number of parallel theoretical projectors which emanate from

an object, to form the image of the object on the projection plane.Pierce Pointsintersections created by theoretical visual rays as they pass through or

collide with a projection plane.

Graphic Imagea symbolic representation of a 3-dimensional part or assembly of

parts, or a schematic layout or organization of entities, projected onto a 2-

dimensional plane.

Normal Viewsviews of features or part characteristics that are oriented perpendicular

to the observers line of sight.

Contiguous Viewsadjacent, orthographically projected views of an object.

Orthogonal Viewsprojected, orthographically aligned views of an object.


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Viewing CubeGlass Box concept; six projection planes configured as a cube.

Fold Linesthe representation of intersections between the sides of the viewing cube.Reference Planesa base line for taking and applying measurements.

Principal Viewsalso referred to asPrimary Viewstypically the front, top, and rightside views.

Surface Viewsnon-normal views of feature surfaces that display 3-dimensional areas.

Edge Viewsall points on a planar surface aligned parallel to the line of sight.

Inclined Surfacesperpendicular to 2 of the 6 viewing planes; parallel to none.

Oblique Surfacesneither parallel nor perpendicular to any of the 6 viewing planes.

Line Weightsthere are three distinct line weightson engineering drawings; thin linesapproximately .007 - .010 wide, medium lines, approximately .015 - .020wide, and thick lines approximately .030 - .040 wide.

Line Typesthere are many line typesthat are used on mechanical drawings, but thereare only six distinct line types that will be used in our discussions regardingorthographic projection: construction, object, center, hidden, phantom, andextension lines (also known as projection, or witness lines).


Orthographic Projection


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9/283Orthographic Projection Table of Contents Master Table of ContentsReturn to the Previous Slide Slide 9 QuitGlossary

Orthographic Projection Theory

Observation of an object begins with the direction from which the object is to be

viewedthe line of sight.



Viewing Station

at Infinity


The viewing station for the observer is always an infinite distance from the object.



Line of Sight

Viewing Station

at Infinity

Projection Plane

(Picture Plane

Viewing Plane)


The plane of projection is located between the viewing station and the object (third

angle projection).



Line of Sight

Viewing Station

at Infinity

Projection Plane

(Picture Plane

Viewing Plane)


The line of sight is always normal to the plane of projection



Object

Line of Sight

Viewing Station

at Infinity

Projection Plane

(Picture Plane

Viewing Plane)


The object may be located anywhere behind the plane of projection



Parallel Visual Rays


Object

Line of Sight

Viewing Station

at Infinity

Projection Plane

(Picture Plane

Viewing Plane)

Because the observation location is at infinity,parallelvisual rays extend from the

object to the plane of projection, and produce the image on the projection plane.



Viewing an Object From an Infinite

Distance

Assuming a position at infinity, and

looking towards the object, we would see

the image of the object on the projection

plane (notice the line contrast between

object, center and hidden lines).

Projection Plane

A permanent image of the

object is formed on the

projection plane by visual

rays as they pierce theplane.

Parallel Visual Rays

Line of Sight

Projection Plane

Object



Visualizing orthographic views using pictorial views



Three-dimensional (pictorial) views of objects are frequently easier to understand thanmulti-view orthographic projections of the same object. Sketching the object in a mannershown can often help students visualize the details of the part. Students who are new tothese concepts are encouraged to use sketches.



GLASS BOX CONCEPT



The glass box concept theorizes that an object is suspended inside a six-sided glass cube

(notice the use of hidden lines on the glass box, depicting lines that would not be visible

from the given perspective).



As the object is viewed from a specific orientation (perpendicular to one of the sides of the cube) visual

rays project from the object to the projection plane. These projectors arealwaysparallel to each other.



The objects image is formed on the projection plane by the pierce points of the visual rays.



The process is repeated to construct the right side view on the profile plane



Similarly, the top view is projected

to the horizontal plane



For many three-dimensional objects, two to three orthographic views are sufficient

to describe their geometry.



The box can be unfolded to show the

multiple views in a single x-y plane


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FRONT

TOP

RIGHT SIDE

Notice that the projectors or extension lines,are perpendicular to the folding lines of theglass box. (Fold lines and extension lines aredrawn very lightly, when used, and are notpart

of the finished drawing.)


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The Glass Box Concept

Click on image to animate - click outside for next slide


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H i h hbj / i i i h hi j i


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Height = h

Width = w

Depth = dIn each of the six principal orthographic views,two specific dimensional characteristics are

provided

Object/Feature Orientation in Orthographic Projection

Directional Orientation in Orthographic ProjectionH i h h


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RIGHT SIDE

d

h

FRONT

TOP

d

w

w

h

Directional Orientation in Orthographic Projection

Two or three views of a 3-dimensionalobject are often sufficient for a complete

definition of part geometry. Width and

depth are displayed in the top view; height

and width in the front view, height and

depth in the side view.

Height = h

Width = w

Depth = d

Directional Orientation in Orthographic Projection H i ht h


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RIGHT SIDEFRONT

TOP

Directional Orientation in Orthographic Projection Height = h

Width = w

Depth = d

Two of the three size characteristics aredisplayed in each view. Because contiguousviews are always projected 90 to eachother, all three dimension characteristics canbe displayed in a single two-dimensionalplane.


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Direction and Orientation

In each projection plane, specific directionalorientation is described.

(Forward, or infront of)

BACK

BACK

LEFT

(To the left of) RIGHT(To the right of)

FRONT

UP

DOWN

FRONT

UP

DOWN

LEFT RIGHT

H

F P

(Behind, or in

back of)

(Forward, or in

front of)

(Behind, orin back of)

(Above, or

on top of)

(Below, beneath,

or lower than)

(Above, or on

top of)

(Below, beneath

or lower than)

(To the left of) (To the right of)


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REVIEW

ORTHOGRAPHIC PROJECTION PRINCIPLES

(Third-Angle Projection)


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The viewing station is an infinite distance from the object.

The line of sight is always perpendicular to projection plane.

The projection plane is always betweenthe object and viewing station.

Visual rays are always perpendicular to the projection plane.

Projectors (visual rays for a specific view) must always be parallel to each other, and

perpendicular to projectors from adjacent views.


REMEMBER,For Third-Angle Projection Solutions,

Review


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FIRST-ANGLE PROJECTION


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Line of Sight

Viewing Station

at Infinity

Projection Plane

(Picture Plane

Viewing Plane)

The basic difference between third- and first-angle projection is that infirst-angle

projection, the objectis placed between the observer and the projection plane.

First-Angle Projection

The image is always projected onto the projection plane but in the case of first


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Line of Sight

Viewing Station

at Infinity

Projection Plane

(Picture Plane

Viewing Plane)

The image is always projected onto the projection plane, but in the case of first-angle projection, it is actually projected away from, instead of towards theobserver. The image would be projected directly behind the object in each case.

Object

The image of the front view is formed as the projectors intersect the projection plane It is


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Projectors

(Visual Rays)

Line of Sight

Viewing Station

an infinite distance

from the object

Projection Plane

(Picture Plane

Viewing Plane)

The image of the front view is formed as the projectors intersect the projection plane. It is

important to note that the front view actually ends upbehindthe back surface of the object.

Let me try to illustrate the concept using three planes of the glass box theory.

Object

Object oriented in first angle


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An illustration of

first-angle

projection. (The

traditional horizontal

(top), frontal, andprofile (right side)

panels of the glass

box have been

removed for clarity.)

You are looking

down on theremaining three

sides of the boxa

birds eye view.

Object oriented in first-angle

projection framework

A bj t h bObject oriented in first angle


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= Line of Sight

An object has been

suspended in the glass

box. Top, front, and

right side views will be

generated using first-

angle projection.

Object oriented in first-angle

projection framework

Fi t A l P j ti Th ll i di t th li


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Front View

First Angle Projection The yellow arrow indicates the lineof sight. The image of the frontview is projected to the projectionplane behind the object.

The top (horizontal) view is projected from above the object but is created on the planeb l


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Front View

Horizontal

or Top View

below.

As with the previous two projections, the right side view is projected to the opposite side of


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Profile or

Right Side

View

Front View

Horizontal

or Top View

the glass box.


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The reference frame can be

unfolded to show the multiple

views in a single X-Y plane

Profile or

Right Side

View

Front View

Horizontal

or Top View

First-angle projection requires that

the box unfold awayfrom theobserver rather than towards the

observer.


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The reference frame can be

unfolded to show the multiple

views in a single X-Y plane

Profile or

Right Side

View

Front View

Horizontal

or Top View

As the box becomes fully two-dimensional, the differencesbetween first- and third-angleprojection become obvious. Theviews are reversed in their order

from third-angle projection; the topview is below the front view and theright side view is to the left of thefront view. If they had beendeveloped, the left side would be tothe right of the front view, the

bottom view would be above thefront view, and the back or aft viewwould be associated with any viewother than the front view.

The United States and Canada are the only two major countries that use third-


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Right Side ViewFront

View

Top

View

angle projection. All other industrial nations throughout the world use first-angle

projection. It is important that you understand the differences because many U.S.

companies are now internationally established. They will expect you to be able to

read and interpret either method used in engineering documentation.


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MULTI-VIEWPROJECTION TECHNIQUES


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Orthographic ProjectionExample Number 1

This is an example of how to use a miter (45) line to assist in constructing an

orthographic solution for the top or horizontal view. The front and right side

views are given.


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1

2

1

2

Explanations regarding solution techniques may vary between instructors, but the

results are the same. Verify the projection by placing extension lines between the

end points of the lineview to view, and label the points (care should be taken to

label the separate views consistently).

Establish a fold line somewhere between the views (make certain that the fold line


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1

2

1

2

(

is perpendicular to the projection lines between the two views). Although the fold

line does not necessarily have to be betweenthe two views, the problem is

simplified by placing it there. Later on, we will discuss placement alternatives.

A second fold line should be constructed perpendicular to the first at some


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1

2

1

2

A second fold line should be constructed perpendicular to the first, at some

convenient location, and extended to overlap both front and side views.


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P j t th i t th t d fi th li (1 2) i th i ht id i i di ti


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1

2

1

2

Project the points that define the line (1,2), in the right side view, in a direction

that isperpendicularto the fold line that is between the view and the 45 miter

line. Remember, when developing a new view, projectors between the views must

alwaysbe perpendicular to the fold lines that separate the two views.

Th i t f d b th i t ti th 45 it li i th j t d


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1

2

1

2

The point formed by the intersection on the 45 miter line is then projected across

the vertical fold line into the horizontal view.

P j t i t 1 d 2 f th f t i i t th h i t l (t ) i N ti


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Project points 1 and 2 from the front view into the horizontal (top) view. Notice

that an intersection is formed by this projection line and the horizontal line

projected from the point on the 45 miter line.

1

2

1

2


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1

2

1

2

Where the two projectors intersect, is the point (end) view of line 1,2. All of the

points are now accounted for in all three views. Label the points.

From a viewing position above the fold line, with the line of sight perpendicular to the


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1,2

1

2

1

2

g p , g p p

projection plane (represented by the fold line), point 1 would be closer to your eye.

Thus, point 1 is in front of point 2 in the labeling of the horizontal or top view.


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Miter Line Technique (Example Number 2)


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Position a fold line at some convenient location between the views. Remember, in


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1

2

1

2

Position a fold line at some convenient location between the views. Remember, in

everycase where fold lines are constructed between adjacent orthographic views,

they must be perpendicular to the projectors.

At some location along the vertical fold line construct a horizontal fold line


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1

2

1

2

At some location along the vertical fold line, construct a horizontal fold line.

Construct a miter (45) line through the intersection of the two fold lines


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1

2

1

2

Construct a miter (45 ) line through the intersection of the two fold lines.

Project points 1 and 2 from the right side view, up to intersect with the miter line.


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1

2

1

2

Project points 1 and 2 from the right side view, up to intersect with the miter line.

At the points where the intersections are formed on the miter line project lines


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1

2

1

2

At the points where the intersections are formed on the miter line, project lines

into the horizontal (top) view.

F h f i j i 1 d 2 i h h i l i l


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1

2

1

2

From the front view, project points 1 and 2 into the horizontal view to complete

the projection of the line.


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Clean up the drawing by eliminating the construction lines.


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1

2

1

2

1

2

The resulting views represent the correct solution for the top, front, and right side


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1

2

1

2

1

2

view of line 1,2.

Miter Line Technique Example Number 3


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Miter Line TechniqueExample Number 3

This drawing represents the top and front views of a line. Construct the right side

viewusing the miter line technique. Label the end points on the line.

Verify the projection of the two views by extending parallel lines which connect


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1

2

1

2

Verify the projection of the two views by extendingparallel lines which connect

the points of the line.

Construct a fold line between and perpendicular to the views of the line


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1

2

1

2

Construct a fold line between and perpendicular to the views of the line.

Next, construct a second fold line perpendicular to the horizontal one, thus


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1

2

1

2

Next, construct a second fold line perpendicular to the horizontal one, thus

establishing the location for the right side view.

Establish the miter line through the point of intersection of the two fold lines.


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1

2

1

2

Project points 1 and 2 in the top view horizontally across the fold line until they


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1

2

1

2

j p p y y

intersect with the miter line.


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Project points 1 and 2 from the front view, across the vertical fold line, into the


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1

2

1

2

right side view.


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Clean up the drawing by removing the projection lines between the views.


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1

2

1

2

1

2

The drawing is now complete, showing the front, top, and right side views of the


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1

2

1

2

1

2

line.

Miter Line TechniqueExample Number 4


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In this problem, front and top views of a skewed planar triangle in 3-D space is given.

An orthographic projection of the right side view is required. Verify the projection.

Set up the right side view by constructing a projection plane.


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1

2

1

2

3

3


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Project the points from both views into the right side view.


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1

2

1

2

3

3

j p g

Connect the points the same way they are connected in the parent views.


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1

2

1

2

3

3

Clean up the construction lines.


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1

2

1

2

3

31

2

3

The required right side view is now complete.


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Mit Li Fl ibilit A S lid Obj t


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Miter Line FlexibilityA Solid Object

Front and right side views are given. Use a reference plane off of the back of the

object to determine the location of the miter line, and project the top view of thissolid object.


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Project vertically from the front view.

Project the back surface vertically from the right side view.


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Establish a horizontal line at a reasonable location along these projectors.


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Where the two projectors (representing the back surface) intersect, construct a 45 line.


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Project the front surface from the right side view until it intersects with the miterline, then project the point of intersection to the horizontal view to complete the

boundary outline of the top view.


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boundary outline of the top view.

The boundary in the top view can be established with object lines, and the drawing

cleaned up.


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