3- Orthographic Projection

MCE216L Engineering Drawing MCE216L Engineering Drawing and Workshopand Workshop

Lecture #3Lecture #3

Orthographic ProjectionOrthographic Projection

Eng. Rami AliEng. Rami AliFall 2015Fall 2015

Line Convention

Multiview drawing (Review )

1st and 3rd Angle projections

Multiviews using Miter line

Contents

Image on a projection plane (or view) depends on a relative orientation between an object and a plane.

Rotate

Tilt

Multiview drawingshows a 2D view of an object.

Axonometric drawing

shows a 3D view ofan object.

View

View comparison

Pictorial drawing

Perspective drawing

Multiview drawing

Difficult to create

Easy to understand Shape and angle distortion

Object looks morelike what our eyesperceive.

Size and shape distortion

Right angle becomes obtuse angle.

Circular hole becomes ellipse

Distortedwidth

Accurate represents an object’s details, i.e. size and shape.

Require an enough practiceto visualization.

Advantage DisadvantageType

Multiview drawing is a set of related images that are created by viewing the object from a different direction.

Width Depth

Height

Width

Hei

ght

Depth

Dep

th

Adjacent view(s)is needed tofulfill the objectdescription.

Multiview Drawing

1. Revolve the object with respect to observer

Methods

2. The observer moves around the object.

Front view Right side view

Top view

Right sideview

Top view

play play

Frontview

Glass box concept

Glass box : Revolution of the planes of projection

Bottom view

Left side view

Rear view

HeightWidth

Dep

th

Relative orientation of views

Left side view Right side view

Bottom view

Top view

Rear view

Front view

Summary : Problem solving steps

1 2

3 4

Given

INTERPRETING VIEWSINTERPRETING VIEWSOne method of interpreting sketches is to reverse the

mental process used in projecting them.

ALIGNMENT OF VIEWSALIGNMENT OF VIEWSAlways draw views in the “standard” arrangement...

Because CAD makes it easy to move whole views, it is tempting to place views where they fit on the screen or plotted sheet and not in the standard arrangement. This is not acceptable.

3D CAD software that generates 2D drawing views as projections of the 3D object usually has a setting to select from third-angle or first-angle projection. Check your software if you are unsure which projection methods are available.

Third-Angle ProjectionThird-Angle Projection

To understand the two systems, think of the vertical and horizontal planes of projection, as indefinite in extent and intersecting at 90° with each other; thefour angles produced are called the first, second, third, and fourth angles (similar to naming quadrants on a graph.) If the

object to be drawn is placed below the horizontal plane and behind the vertical plane, as in the glass box you saw earlier, the object is said to be in the third angle. In third-angle projection, the views are produced as if the observer is outside, looking in.

First-Angle ProjectionFirst-Angle ProjectionIf the object is placed above the horizontal plane and in front of

the vertical plane, the object is in the first angle.

The biggest difference between third-angle projection and first-angle projection is how the planes of the glass box are unfolded.

Transferring Depth DimensionsTransferring Depth Dimensions

You can transfer dimensions between the top and side views either with dividers or

with a scale.

The depth dimensions in the top and side views must correspond point-for-point. When using CAD or instruments,

transfer these distances accurately.The use of MITER LINE provides you fast and accurate method of constructing the 3rd view once two views are established.

Transferring a depth : miter line

miter line 45o

Extension lines

Object featuresEdge is a line that represent the boundary between two faces of an object. Surface limit is a line that represents the last visible part of the curve surface.

Prism Cylinder Sphere

No edges!

Surface is an area that are bounded by edges or surface limit. Surface can be plane or curve.

These features will appear as lines in a multiview drawing.Note

Class activity : Object’s features

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34

5

6

7

8

Identify name of the featuresdenoted by a NO. 1 to 9?

1

2

3

4

5

6

7

8

Edge Surfacelimit

Surface

Skip test Next slideReset all

B

AF BF BRAR

AT

BT

Projection of a normal line

A

Play

Glass box concept Multiview drawing

AR

BR

AT

BT

AF BF

Projection of a normal plane

Play


Projection of an object

Play


Do the same procedures forall remaining edges (or planes)

Hidden line is usedto show existence of

a hidden edge.

Projection of an inclined line

Play


AF

BF

AF

B

A

BF

AR

BR

AR

BR

AT

BT

AT

BT

Projection of an inclined plane

Play


Projection of an obliqued line

Play


AF

B

A

BF

AR

BR

AT

BT

AF

BF

AR

BR

AT

BT

Projection of an obliqued plane

Play


Projection of a curve line

Play


AFBF

CF

BR

AT

BT

CT

AR

CR

B

AC

AFBF CF BRAR CR

AT

BT

CT

Projection of a curve surface

Play


VIEWS OF SURFACESVIEWS OF SURFACESThere are terms used for describing a surface’s orientation to the plane of projection. The three orientations that a plane surface can have to the plane of projection are normal, inclined, and oblique.

Note how a plane surface that is perpendicular to a plane of projection appears on edge as a straight line

ANGLESANGLESIf an angle is in a normal plane (a plane parallel to a plane of projection) it will show true size on the plane of projection to which it is parallel.

If a flat surface is viewed from several different positions, each view will show the same number of sides and a similar shape. This consistency of shapes is useful in analyzing views.

Example

Projection of an object havingcurved surface and plane

In the case of intersection, an edge exists and becomes a line in a multiview drawing

Curved surface can either tangent or intersect with an adjacent plane or adjacent curve surface.

In the case of tangential, there is no edge and line in a multiview drawing

I

I

T

T

T

I

Examples

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3

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4

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1

Examples

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5 6

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Examples

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9

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10

No line exists

Line Convention

Line convention

Precedence of coincide lines

Hidden line drawing

Center line drawing

Precedence of line

When lines coincide witheach other, the moreimportant lines cover upthe other lines.

Order of importance(from high to low) is- visible line- hidden line and- center line.

Line convention

Play

What is an appropriate line type to replace the lines NO. 1-4?

1

2

3

V H C


“V” denotes visible line

“H” denotes hidden line

“C” denotes center line

Class activity : Precedence of lines

12 3

4

4

Hidden line drawingHidden line should join a visible line, except it extends from a visible line.

joinspace

join

space

spacespace

Hidden line drawingIntersection between hidden lines should form L, T, V or Y corner.

L T

inside

VY

L T

A curve hidden line should start on a center line.

Hidden line drawing

Line convention

Center line drawing

In a circular view, short dash of a center line should cross at the center of the circle or arc.

Center line should always start and end with long dash.

Center line should not extend between views.

Leave space Leave space

Play Play

3~4 mm

3~4 mm

Center line drawingFor a small hole, a center line is presented as a thin continuous line.

Leave a gap when centerline forms a continuation with a visible or a hidden line.

Play

Leave space Leave space Leave space

Line convention

Class activity : Hidden line drawing

correct wrong

correct wrong


MultiViews ExamplesMultiViews Examples

Class WorkClass WorkDraw the Front, Plan, and side multiviews (orthographic projections) for the following parts

1 Using 3rd Angle method 2 Using 1st Angle method 1 Using 3rd Angle method

Documents

3- Orthographic Projection