Engineering Drawing Principles.

PSSD 1.

Mike FelsteadSECaM

October 2005

A Brief Introduction to the Production of Engineering Drawings to BS8888.

Introduction

• What is an engineering drawing?– A concise ‘set’ of instructions to manufacture a component without

need to refer to an external source for further information.• 1 sheet of paper. • 1 component drawn using orthographic layout techniques.• Fully describe all geometry via a series of standard ‘views’. • Dimension to fully define the size and form of all features.• Detail material, finish and tolerances required, and quantities.

• What you need to do…– Learn to ‘read’ and understand engineering drawings.

• Ref: Manual of Engineering Drawing, Simmons & Maguire.– Work to BS8888 (Engineering drawing practice for schools and colleges).

• Copies available in 207, Student Workshop and Library.

Engineering Drawing - Key Features

Title Block

• Title Block contains:– Drawing Name.– Date drawn (version number).– Projection system.– Scale.– Material, tolerances, surface finish, etc…

Engineering Drawing - Key Features

Drawing Views Section

View

Partial View

Types of Engineering Drawing

• Part Drawing– A single component.– Contains all

manufacturing data.– Views are dependent

upon complexity.

Types of Engineering Drawing

• Assembly Drawing– Shows components in their physical relationship.– Small assemblies may feature a ‘Parts List’.– Assemblies can be sub-assemblies.

SolidWorks DrawingsSolidWorks is an advanced 3D CAD modelling system.

These systems will produce your drawings automatically.

But beware! They’re not perfect, you will have to tidy them up manually.

Projection Systems – First AngleFirst Angle – the model view is drawn opposite to the face being viewed.

Remember: COe is FIRST THROUGH the tape.

BS8888 First Angle Projection Symbol.

Projection Systems – Third AngleThird Angle – the model view is drawn adjacent to the face being viewed.

BS8888 Third Angle Projection Symbol.

Drawing Layout – Setting Out The Views

Keep it neat!

Balance the layout on the page.

Don’t forget to leave room for the dimensions!

Drawing ViewsHow many views to describe this

component?

Six views would cover all sides!

Not in this case! But it’s not impossible

Two views will describe it… and some ‘hidden detail’will uncover all the features.

Line TypesDifferent types of line are used to indicate different aspects of the drawing.

Most 3D CAD software will automatically use the correct line type.

With 2D CAD software you generally select the line type required.

Outlines 0.7mm – show boundary of component view.

Dashed 0.35mm – hidden detail...

Chain 0.35mm – centrelines, section views...

Leader 0.35mm – dimensions, leaders…

DimensioningA drawing means little without full dimensioning.

Each dimension should appear only once.

No calculation of dimensions should be necessary.

Dimensioning

Chain Dimensioning.Auxiliary dimensions (in brackets)

avoid need to calculate from primary dimensions.

Parallel Dimensioning.Can require lots of room to layout!

Remember – Clear, well laid out, complete!

DimensioningCarefully compare the layout of the dimensions on the two sides of

this component drawing.

Sections and Sectional ViewsUsed to expose features clearly for dimensioning, important when

hidden detail must be shown.

Partial Views

Used to clarify a specific area or feature. In this example the

double wall of this end of the bracket is made obvious and

additional dimensions can thus be added.

Magnifies small features. In this example the fine detail of the

grooves are magnified 5X, dimensions would be added to

fully define them.

Engineering Drawings – Key Points

What is an Engineering Drawing?

Key Features – Title Block, Views, etc...

Drawing Types – Part and Assembly.

Drawing production with 3D CAD.

Projection Systems – 1st and 3rd Angle.

Drawing Layouts and Views.

Line Types.

Dimensioning.

Sectioning and Partial Views.

Software has made the production of engineering drawings much simpler and quicker – but it still falls to you to ensure the drawing is

correct and to standard.

Sketching

As a professional engineer you will

often be required to produce quick initial sketches of design

concepts.

It may be a freehand sketch, but

engineering drawing principles still apply!

And finally Isometric Projection...

Isometric ProjectionA classical method of showing all 3 axes of space in one 2D representation.

Most easily understood through 3D CAD which shades the model to help the eye ‘see’ a 3D image…

Imagine you’re in a helicopter hovering just off the corner of a building –if your position was precise enough you’d have an isometric view.

The Cube The Swivel Bracket

Summary

• A brief overview of what’s in an Engineering Drawing– Title Block, Layout, Projection, Views, Dimensions, etc…

• 2D and 3D CAD– Drawings can be ‘automatic’ – but will always need tidying up!

• BS8888 Manual – in 207, Student Workshop and Library– Every drawing or sketch you produce should meet this standard!

• And finally…– Don’t fret, the rules are basic! Just keep it neat, tidy and clear!