Technical Drawing

Designing things on paper

Conceptual Sketches

• When you first get an idea for something you want to build you may draw it roughly, without using instruments or accurate scales. This is called a conceptual sketch.

Types of Drawings

Artistic

Sketches (conceptual)

Diagrams

(design & technical)

Drawings

(technical/engineering)

Diagram (design plan)

All Drawings

Technical

Diagram (technical)

simulated

perspective

Oblique projection

Isometric projection

Multi view orthographic

Less technical More technical

• A conceptual sketch…

– Allows an idea to be

expressed quickly in graphic

form

– Is prepared free-hand (without

drawing instruments)

– Is not done to scale, but it

respects the rules of technical

drawing as much as possible,

and is made roughly

proportional to the object

represented.

Technical Drawings

• Serve as a reference to workers, architects or machinists.

• When you are ready to design the details, you make a technical drawing, done with more detail and more accuracy.

Difference:

• Sketch: made without drafting tools...

Just pencil and paper. Scale is

approximate, not accurate, but the sketch

should still look like the object.

• Drawing: made with drafting tools...

Ruler, set squares, protractor and

compass. Scale should be accurate and

the drawing carefully made.

A technical drawing…

Presents all the information necessary for the object’s construction.

Is made with great precision,

Requires the use of rulers, compass and protractor or drafting software.

Is done to scale, and respects the proportions of the object represented.

Respects conventions in the mode of the representation.

Basic Lines (part 1)

Visible

(Object) Line

Represents the

outline

Thick Draw the visible

object edges

with these lines

Hidden Line Shows hidden

details

Medium

dashed

Draw hidden

edges with

these

Construction

Line

Used during

drafting

Fine Faint lines,

sometimes

coloured

Dimension

Line

Used to indicate

a dimension

Fine, with arrows

8cm

Dimension &

extension lines

go together!

Extension

Line

Used with a

dimension line

Fine Near arrows

Center

(Axial) Line

Shows center or

symmetry

Fine With dash in

middle

8 cm

Basic Lines (part 1)

Ghost Line Shows possible

movement

Fine dashed

Sometimes in

other color

Cutting

plane line

Position of a

cross-section

Thick With arrows

Used only if you

plan to draw a

cross section

Hatched

Lines

Surface of a

cross-section

Fine Show where it

is solid (section

view only!!)

Long Break Shows that a

line is shortened

Fine With zig-zag

Used only for

large objects

Short break

(cutaway)

Object shortened

or cut away Medium With curve

Leader Line Points to

something

Fine With bent

arrow

Attaches a comment

or angle or dimension

to an object.

Technical Drawing of Fighter Plane (Isometric Projection, exploded view)

Technical drawings can represent things…

as simple as a spoon,

or…

Technical Drawing of a spoon

Multi-view, Orthographic projection

• as complex as a space ship

Photograph of Mercury Spacecraft

Technical Drawing of Mercury Spacecraft, Top View, Orthographic

Technical Drawing of Mercury Spacecraft, Isometric Projection

Projections

• Perspective projections

• Multi-view projections

• Isometric projection

• Oblique projection

True Perspective

• Objects drawn in true perspective look realistic.

• They have “vanishing points” where straight lines seem to converge

• They can have one, two or three vanishing points, depending on how much the artist wants to work.

• But in true perspective, objects far away will be drawn smaller than nearby objects… not a good idea in technical drawing!

Vanishing Point

Vanishing Points

Vanishing Points

More True Perspective Drawings

• Now that you have seen how nice

perspective drawings can be...

• FORGET ABOUT THEM! – We hardly ever use perspective projections

when doing technical drawing.

– They are too much work, and they don’t show

all the details we may need to show.

– Also, they distort both angles and dimensions.

• Leave them for ART class...

Isometric Projection (a simulated perspective drawing style)

• Isometric (or simulated perspective) drawings look at first like perspective drawings…

• But the lines don’t converge. There are no vanishing points and distant objects are the same size as nearby ones.

• Right angles in isometric projections are usually represented by 60° or 120° angles.

60˚ Represents 90˚

Represents 90°

More isometric drawings

Warning: Your workbook classifies isometric drawings as “perspective”

drawings, but they are not true perspective. They resemble perspective

drawings but in a true perspective drawing, distant objects are drawn smaller.

In isometric drawing, distant objects are not smaller..

Oblique Projection another “simulated” perspective

• Similar to isometric projection, it

is also a “simulated perspective”

• In oblique projections, the side

of the object facing you is drawn

“square” and accurate (that is

with right angles at 90° and its

measurements proportional)

• The sides not facing you are

distorted • Warning: Your workbook calls this oblique

perspective, but it is not a true perspective.

90°

90° =60°

This side is

accurate

This side

is not!

Orthographic Projections

• Orthographic projections “flatten” one view

of the object onto a sheet of paper, while

retaining the correct proportions (angles

and dimensions)

• Maps are an example of orthographic

projection (a top view)

• The trouble with orthographic projections

is that one view usually isn’t enough. • Maps and floor-plans are exceptions, where one

top-view is often enough.

Orthographic Projection (Multi-view)

• Draws an object as it would be seen from several different directions

• The views are “flat”, with all angles shown correctly and all measurements to scale.

Comparing Projections

• Perspective drawings look nicer

when used by an artist, but…

• Isometric, oblique and multi-view

drawings give more accurate

information when used in

technical drawing.

• Isometric drawings show accurate

dimensions, but distorted angles.

• Oblique drawings give accurate

dimensions for one side only.

• Orthographic (multi-view) are the

best choice for most technical

drawing.

Oblique

Orthographic

(multi-view)

Comparison of Projections

Projection Used for Tested on

Orthographic (top view)

Drafting, maps, floor plans Yes

Orthographic (multi-view)

Technical drawings,

drafting, conceptual

sketches (sometimes)

Yes

True Perspective (one, two or three point)

Artistic drawing, conceptual

sketches

No

Isometric (simulated perspective)

Conceptual sketches,

technical drawings (sometimes)

Yes

Oblique (simulated perspective)

Conceptual sketches No

An Isometric Drawing

Scale

• SCALE is the relationship between the

measurement of an object drawn on a sheet

of paper, and the measurements of the actual

object.

• Often technical drawings are made a different

size from the objects they represent.

• Scale-reduction is when the drawing is smaller

than the actual object

• Scale-increase is when the drawing is larger

than the actual object.

Dimensioning

• When a drawing is done to scale, you should

label it with its dimensions. • Use dimension lines to label each dimension, with

extensions where necessary

• You should label just enough edges to show all the

dimensions, but you don’t need to repeat.

• In Canada (at least for science) dimensions are

usually given in millimetres (mm). If you use different

units (cm, in, feet etc.) you need to write the unit. You

do not need to write mm if all of your dimensions are

in millimetres.

• Angles can be shown in degrees (°), diameter by Ø,

and radius by R

Dimensioning 300 means 300mm unless another unit is

specified

Ø means diameter

(R would be radius)

A Toy Truck

How to label

an angle.

How to label small

dimensions.

Dimensioning Dimensions can also be

shown on isometric

drawings, but you have to

be a bit more careful.

Also, you should only

show the most important

dimensions on an

isometric drawing.

Diagrams

• Diagrams are simplified versions of a

drawing. Diagrams show how an object

works, not necessarily how it looks.

• Diagrams often use abstract symbols

rather than actual pictures to represent

things.

A Circuit Diagram

– Doesn’t show what the circuit looks like, but

tells an electrician how its all connected.

Diagram of Energy Conversion Unit

– It doesn’t show what the unit looks like, but rather,

what it does or how it works.

Exploded Views

• A diagram that shows an object “taken

apart” is sometimes called an exploded

view.

Chapter 11 Questions • 1. Two common drawings used in technology are:

Engineering (or technical) Drawings and Diagrams.

• 2. Technology is a set of techniques used by humans to

design, build, and maintain objects and systems that we

need or want.

• 3. (a) Basic Line (b) Function

1 Dimension Line Indicates the length of an object

2 Extension Line Shows boundaries of a measurement

3 Visible (or Object) Line Shows Visible outlines of an object

4 Hatching Indicates surface in a section view

5 Leader (or Reference) Line Ties a dimension (or a label) to a feature

6 Hidden Line Indicates hidden outlines

7 Centre (or symmetry) Line Indicates the center of a circle

(c) Cutting Plane lines and Construction Lines are not shown.

• 4. Geometric Lines • A) the main drafting instruments are: T-square,

set-squares, ruler, pencil and compass

• B) The three types of straight line are: horizontal,

vertical, and oblique.

• C) Two drafting instruments that can draw circles

are the compass and the circle template.

• 5. The Stop Signs: The stop sign on the left is a

sketch, since it appears to be drawn freehand. The one

on the right was drawn using tools.

• 6. Projections: • A) The rays are perpendicular in multi-view and

isometric projections

• B) these are called orthogonal projections

• 7. The six views are: • Top view, Front view, Right Side view

• Bottom view, Back (or Rear) view, Left Side view

• 8. The three drawings: • #1 oblique projection, #2 isometric, #3 multi-

view (or orthographic view)

• #1 and #2 are the “perspective” drawings. (actually

they are “simulated perspective” drawings rather than true

artistic perspective)

• 9. Views • A matches 3, B matches 1

• C matches 4, D matches 2

• 10. Jonathan is building a model car. He is

reducing the measurements 40 times.

• The scale he is using is a scale reduction.

• It is indicated by 1:40

• The finished model will be 100 mm long (or 10 cm)

• 11. The diagram of the soccer field has a scale

of 1:2000, so... (hint: use your ruler)

• The width of the actual field is 68000 mm (or 68m)

• The length of the actual field is 104000 mm (104m)

• 12. The dimensions of the skateboard are:

• Length = 790 mm (or 79 cm)

• Width = 210 mm (or 21 cm)

• Diameter of wheels = 60 mm

• 13. The maximum difference between the

measurement on the diagram, and the real-life

measurement is called the tolerance.

• 14. Match the objects to their cross sections:

• A matches 1

• B probably matches 3, (but could match 2)

• C probably matches 2, (but could match 3)

• 15. Look at the diagram of the wrench. • Section [B] is octagonal

• Section [C] is circular (or round)

• The sections are aligned, they are shown inside

the drawing of the wrench instead of outside of it.

• 16. Diagram of kitchen scale • A) The force is exerted on the tray

• B) 7 regular screws were used, plus one bolt (which

is a type of screw) so I would also accept an answer

of 8.

• C) The rod can move up and down ( or, more

accurately, has bidirectional translation)

• D) The coil spring allows the rod to return to its

initial position.

Define: • Technology Technical Drawing

• Basic Lines Geometric Lines

• Sketch Projection

• Isometric (projection) Oblique (projection)

• Orthagonal (proj.) Multiview (projection)

• General drawing Exploded drawing

• Detail drawing Scale

• Dimensioning Tolerance

• Section Cross section

• Diagrams: design, technical, and circuit

Basic Lines to Know

• Visible(or object)

• Hidden

• Construction

• Centre

• Dimension and extension

• Cutting Plane

• Hatching

• Leader (or reference)

Geometric Lines to know

• Horizontal (straight)

• Vertical (straight)

• Oblique

• Ellipse (and circle)

• Curve

Methods of Drawing

• Sketching

• Drafting

• Computer Assisted Design (C.A.D.)

Projections

• Multiview (orthagonal)

• Isometric

• Oblique

Scale

• Dimensioning

• Calculating Scale

Diagrams

• Design plan diagrams

• Technical diagrams

• Circuit diagrams

• Symbols for

– Forces or constraints

– Movement

– Parts (screw or bolt, nut, guides)

– Electrical circuits