Agenda-Day 2

• Projections

• Standard Views

• Dimensioning Practices

• AutoCAD Tips for Lab

Engineering Drawing

• Definition:

• Binding legal document that disclosed graphically and in text the form and function of an object.

• Legally binding if created or approved (i.e. stamped) by a professional engineer.

Representing 3D Objects

Projections

• Two basic types

• Perspective

• Parallel

• The objective of technical graphics is not necessarily to present what the eye can see . . .

Perspective Projections

• It essentially what the eye can see

• Common in artistic graphics

• Not as common in technical graphics

• Requires the eye to be a an infinite distance to mitigate distortion

• Exception: virtual environments

Parallel Projections

• Parallel lines of sight

• Define a projection plane• Between the viewer

and object

• Less realistic but much better in terms of accurately representing the features of an object

Parallel vs. Perspective . . .

Types of Parallel Projections

• Oblique-projection direction not orthogonal to viewing plane

• Orthographic - projection plane orthogonal to viewing plane

• Axonometric

• Isometric – shows each direction equally

• Projection plane intersects each coordinate axis at the same distance from the origin

• Multiviews

• Three 2D views

Orthographic vs. Oblique Projections

Axonometric Projections

Isometric Trimetric

30 deg Isometric

1/2 Isometric

Military Isometric

Types ofIsometric

Multiviews for Representing 3D Objects

Movie!

http://highered.mcgraw-hill.com/sites/0073136069/student_view0/chapter5/animations.html#

Standard Multiview Orientation

• Right Side, Top, Front

• Front is the central view

• Top can also be the standard view

Representing 3D Objects with Multiviews

• Number of possible views?

• Answer = 2

• Referred to First and Third Angle Views

First vs. Third Angle Projections

Resulting Standard Views

Front Right

Drafting Practices

• When to use Diameter vs. Radius.

• Over-dimensioning.

• Implied geometry.

Diameter vs. Radius

• Use diameters to dimension holes

• Use radius dimensions for features that have a constant radius but are not a complete hole.

D vs. R

D1.000

R2.0

Dimensioning the Same Feature Twice

O 0.500

O 0.5002.000

0.750

1.250

Default tolerance +/- 0.005

Bad PracticeWrong

(Two different interpretations)

Tolerance Stacking . . .

2.000

0.750

1.250

Default tolerance +/- 0.005

(1.995 to2.005)

(1.990 to2.010)

Implied FeaturesNot typically dimensioned

• Perpendicularness

• Parallelism

• Some symmetric features

FIL E N A M E : Im port_Floor_C hisel-R ev 1.dw g

L A ST R E V ISIO N : 5 /8/03

B A L T IM O R E T O O L W O R K S, IN C .

PA R T : Im port F loor C hisel

D R A W N B Y : J. G lancey, P .E .

D A T E : 5 /8/03

M A T E R IA L : A ISI 6150 (Fine G rain/Special Q uality) S teel H ex

DimensioningOther Rules of Thumb

• Use font sizes that can be read.

• Try not to place dimensions or leader lines on the part.

• Use comments and notes whenever possible to minimize the number of dimensions required.

• Keep dimensions within the drawing boundary.

On-Line Assignment

• Chapters 1 to 6

• Take the Quiz one time only

• True-False or Multiple Choice (you choose)

• No Homework this week

Lab 2

• Directions and Example available on the Schedule Page

• Tips to Cover:

• Status Bar

• Drawing Layers

• Text Style Managers