INTRODUCTION TO

TECHNICAL DRAWINGDr. Mark Yuly

PHYS 215 Statics and Engineering Design

Visualization and Drawing

Visualization – ability to create and manipulate mental image.

Drawing – ability to put it on paper.

Why is this important?

I. Images can be visualized by showing how an

objects geometric elements are related.

Faces (“planes”) Reflect the light that we see.

Edges (“lines”) Two faces intersect.

Abrupt change in contrast.

Vertices (“points”) Three or more edges intersect.

Curves Surface limits.

face

edge

vertex

Surface limit

Example:

Semi-Cylinder

II. Pictorial Projections

A. Perspective Projection

1. True depth perception.

2. Most natural looking.

3. Hard to sketch quickly.

Projection

plane

object

II. Pictorial Projections

B. Parallel Projections

1. View at ∞.

2. Projection lines are ∥.

3. Easier to use.

III. Parallel Projections

A. Orthographic Projection

1. LOS is always ⊥ to projection plane.

2. Only see one side of object at a time.

III. Parallel Projections

B. Oblique Projection

1. LOS is intersects

projection plane at

angle other than

90°.

2. Front face is true-

size, other faces are

distorted.

3. Use when most detail

on front face.

III. Parallel Projections

C. Isometric Projection

1. Rotate object so

front face is not ∥ to

projection plane.

2. Use for features on

multiple sides.

V. Orthographic

Projections

A. Formed by taking orthographic projection of each side – then “unfolding”…

B. Views:TopFrontRight

Bottom RearLeft

Only use as many as needed.

C. Hidden linesUse views with fewest hidden lines.

} standard

V. Orthographic projectionsD. Standard location and orientation.

front

rear left

bottom

top

right

V. Orthographic

projections

E. Types of lines

Also: Construction lines

1. Preliminary layout work.

2. Very thin and light.

3. Avoid having to erase.

http://www.ic.arizona.edu/ic/ce210/lines.htm

V. Orthographic

projections

E. Types of lines

Alphabet of Lines

Name Line Description Sizes Examples

Construction

Line

A lightly drawn line

that shows the shape of

an object.

A light thin solid

line.

Border

Line

A very thick line that

frames the drawing.

A very thick solid

line.

Visible

Object

Line

A thick line that shows

the form of an object.

A thick solid line.

Hidden

Object

Line

A thin line that has

broken dashes. It

shows a hidden edge.

Dashes are 3 mm

long with 0.75 mm

spaces.

Centre

Line

A thin line with long

and short dashes. It

indicates the centre of

objects and shows that

an object is symmetrical

about a line.

Long dashes are

25 mm long and the

short dashes are 3

mm with 1.5 mm

spaces.

Extension

Line

A thin line used to

extend the size of the

object so that the

dimension can be

placed near the view.

A thin solid line that

projects from an

object. Starts about

1.5 mm after object

line and ends about

3 mm beyond the

last dimension line.

Dimension

Line

A thin line with

arrowheads on each end

that touch the extension

line. It is opened for

the dimension.

A thin solid line the

length of each

dimension. Should

start at about 10 mm

away from the

object line.

50

30

Leader

Line

A thin line with an

arrowhead on one end

and on the other end is a

dimension or note.

A thin solid line

used to show the

parts related to the

note or dimension.

www.ijs.k12.nf.ca/Tech_Page/grade8_tech/Alphabet%20of%20Lines.doc

The Plan This week: 2D drawings

Download AutoCAD

Download “AutoCAD 2020 Tutorial First Level” sample chapter

Complete the two drawings in the tutorial.

Look up how to add dimensions (Google).

Next week: 3D drawings in Inventor