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

• 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.

• 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.

• A technical drawing…– Presents all the information necessary for the

object’s construction.– Is made with great precision, requiring the use

of rulers, compass and protractor.– Is done to scale, and respects the proportions

of the object represented.– Respects conventions in the mode of the

representation.

• A technical drawing…– Presents all the information necessary for the

object’s construction.– Is made with great precision, requiring the use

of rulers, compass and protractor.– Is done to scale, and respects the proportions

of the object represented.– Respects conventions in the mode of the

representation.

Basic Lines (part 1)

Object Line Represents the outline

Thick

Hidden Line Shows hidden details

Medium dashed

Construction Line

Used during drafting

Fine

Dimension Line

Used to indicate a dimension

Fine

Extension Line

Used with a dimension line

Fine

Axial Line Shows center or symmetry

Fine

Basic Lines (part 1)

Ghost Line Shows possible movement

Fine Sometimes in other color

Cutting plane line

Position of a cross-section

Thick

Hatched

Lines

Surface of a cross-section

Fine

Long Break Shows that a line is shortened

Fine

Short break

(cutaway)

Object shortened or cut away

Medium

Leader Line Points to something

fine

• As simple as a spoon,

• Or…

• Or as complex as a space ship

Projections

• Perspective projections

• Multi-view projections

• Isometric projection

• Oblique projection

Perspective

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

Multi-view projection

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

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

Isometric Projection

• Isometric (or false 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.

More isometric drawings

Oblique Projection

• Similar to isometric projection, it is a “false perspective”

• In oblique projections, the side of the object facing you is drawn “square” that is with right angles at 90°

Isometric vs. Perspective• Perspective drawings

look nicer, but…• Isometric drawings give

more accurate information.

• Perspective drawings are used by artists, isometric are used in technical drawing.