06 H191 W02 D02 1-2 V1.4 - Projection Systems - Ortho and Iso 08

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First-Year Engineering Program

1Autumn 2008

Engineering H191

Engineering Fundamentals and Laboratory I

Lecture 06

Projection Systems: Orthographic and

Isometric




2Autumn 2008

Objectives

Orthographic Projections

View Selection

Glass Box Approach First and Third Angle Projections

Line Precedence

Two View Drawings

Tips




3Autumn 2008


Reference: Technical Graphics, Chap 3:

Advantage ± Represent features of an object

more accurately

Example Problem




4Autumn 2008


Orthographic Projections are a collection of 2-Ddrawings that work together to give an accurateoverall representation of an object.




5Autumn 2008

Defining the SixPrincipal Views or

Orthographic Views




6Autumn 2008

Which Views to Present?

General Guidelines

Pick a Front View that is most descriptive of

object

Normally the longest dimension is chosen as the

width (or depth)

Most common combination of views is to use:

± Front, Top, and Side View

Any other view different from the Principal Views

is called an Auxiliary View (see 3.15 in the

Technical Graphics text)




7Autumn 2008




8Autumn 2008

Glass Box Approach

Most powerful technique to understandorthographic projections

Suspend the object with transparent stringsinside a glass box

Freeze the view from each direction (each of the

six sides of the box) and unfold the box

Animation illustrates glass-box approach




9Autumn 2008

Glass Box Approach Available on the FEH website:

Go to : http://feh.osu.edu

± Click ³AU Materials´ on left to find:

Syllabi for FEH courses

Engineering H191 Lecture notes

Other Materials - Glass Box Animation




10Autumn 2008

Glass Box Approach




11Autumn 2008

Glass Box Approach




12Autumn 2008

Glass Box Approach




13Autumn 2008

Glass Box Approach




14Autumn 2008

Glass Box Approach




15Autumn 2008

Glass Box Approach




16Autumn 2008

Third-angle Projection

First-angle Projection

First and Third Angle Projections

First Angle ± International

Third Angle ± U.S.




17Autumn 2008

Conventional Orthographic Views

Height

Depth

Width

Front View

Top View

RightSide

View




18Autumn 2008

Are The Orthographic Views OK?




19Autumn 2008

Orthographic Must Be In Projection




20Autumn 2008

Hidden and Center Lines

Hidden Line ± used to represent features that

cannot be seen in the current view

Centerlines ± used to represent symmetry and to

mark the center of circles and the axes of

cylinders, and the axes of symmetrical parts,

such as cylinders and bolts




21Autumn 2008

For Example:

1. Visible

2. Hidden

3. Center




22Autumn 2008

Visible lines takes precedence over all other lines

H idden lines and cutt ing plane lines take

precedence over center lines

C ent er lines have lowest precedence

Precedence of Lines

0.70 mm

0.35 mm

0.35 mm




23Autumn 2008

Example:

A ppli c at ion of Prec edenc e




24Autumn 2008

Intersecting Lines in Orthographic Projections

Solid Line Intersections

Dashed Line Special Case Intersections

Gap




25Autumn 2008

Two-View Drawings

Some objects can be fully described by two views,

look for:

± Symmetry or Bodies of Rotation

Front View Right Side View Front View

RightSide




26Autumn 2008

Other Two-View Examples




27Autumn 2008

Summary

Introduced to orthographic projections

We recommend the software animation exerciseintroduced in class. Animation can be found on

the FEH web site under additional materials ±

Glass Box Theory.




28Autumn 2008

Review Questions

Rectilinear grids are used for sketching

isometric pictorials « True/False

Based on the lines of sight, orthographicprojection drawings are classified as

___________ projections

There are ____ standard principal views of

orthographic projections

Each view in an orthographic projection

concentrates on ____ dimensions of the object




29Autumn 2008

Hints for Orthographic Projection Sketching

Identify the major features and overall

dimensions of the object

Do not use any straight-edge devices as a pencilguide when sketching by hand

Start by drawing bounding boxes with light

construction lines.

Keep views aligned while sketching




30Autumn 2008


Title Information is required ± follow conventions

Usage of construction lines is encouraged.

± Mandatory for circle or ellipse

Orthographic projection:

± Alignment of the views is important!

± Will not be graded, if not aligned




31Autumn 2008


Follow the precedence of lines

Darken all visible, hidden, and center lines

Map inclined and oblique faces to all three views

± Inclined faces appear foreshortened in two views and as a

line or an edge in the other view.

± Oblique surfaces appear foreshortened in all views buthave the same characteristic shape (triangle in this case)

Foreshortened

Edge or Line

Foreshortened

Inclined surf ace Oblique surf ace




32Autumn 2008

Sketching a Circle

Draw a square whose

sides are the diameter

of the circle.

At the center of eachside define the point of

tangency for the circle.

Draw the diagonals of

the square.

Orient the paper so you

can draw equal arcs to

construct the circle




33Autumn 2008

Today's Assignment

T15

TG 2.6 and 2.17

06 H191 W02 D02 1-2 V1.4 - Projection Systems - Ortho and Iso 08

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