ENGINEERING GRAPHICS Engineering is a creative profession: … engineers create what has never been’ Why graphics ? Why engineering ? … a universal language … used in creation and communication ‘scientists explore what is …

But graphic images from 15,000-18,000 BC communicate very effectively today Red ochre cave painting Vallon-Pont-d'Arc, France

A universal graphic language? Egyptian hieroglyphs were based on recognisable graphic symbols

Chinese characters became much more abstract

Many Western languages use standard symbols, but not in a universal way … Hello Bon Jour Guten Tag G’day...

Sketches Leonardo da Vinci ( ) Perspective projection Parallel projection We will study ‘orthographic’ projection systems in detail

a printer Imagine trying to describe this printer, precisely, using verbal communication

Orthographic projection Multi-view drawings provide the most accurate description of 3D objects and structures for engineering, manufacturing, and construction requirements

Classical Projections

Orthographic Projection The word Orthographic means 'to draw at right angles'. Hence orthographic projection is a means of visualising an object by projecting its edges at right angles onto the projection plane. In practice, orthographic projection uses two main planes, called the principal planes of projection or planes of reference

Orthographic Projection Projectors are orthogonal (90°) to projection surface

Orthographic Projection In engineering, there are two systems of projection: –First Angle Projection – Europe, Asia and former European colonies in Africa and parts of Australia –Third Angle Projection – Used in the USA and Canada, in Africa where American development is taking place and parts of Australia

First Angle Projection Fist Angle Projection - object positioned in space in the First Quadrant. View on the vertical plane - ELEVATION View on the horizontal plane - PLAN To obtain the views as they would appear on a sheet of paper, the horizontal plane is opened out about the intersection of the planes. The line of intersection is called the XY line, ground line or folding line.

Perspective Projection

Parallel Projection

Glass projection box End elevation Plan Elevation

YY line or fold line Vertical plane End vertical plane Horizontal plane XY lines or fold lines

Vertical plane End vertical plane Horizontal plane YY line of fold line XY lines or fold lines Elevation End elevation Plan

End vertical plane Vertical plane Horizontal plane

Front Elevation End Elevation (Left) End Elevation (Right) Plan View

First Angle Plan View Front Elevation End Elevation (Left) End Elevation (Right)

Advantages and Disadvantages Preserves both distances and angles –Shapes preserved –Can be used for measurements Building plans Manuals Cannot see what object really looks like because many surfaces hidden from view –Often we add the isometric (3D)