LECTURE 1ENGINEERING GRAPHICS 232

Fundamentals of Engineering Drawing

Introduction

Engineering graphics is is a graphical communication language of engineers, a system of communication, which employs lines,

characters and symbols to represent three-dimensional objects two-dimensionally

used to represent initial concepts and final working drawings

Methods for producing engineering drawings: Sketching Manual Drafting Computer-Aided Drafting / Drawing (CAD)

Sketching/freehand drawing

is one of the quickest ways to graphically express ideas, concepts and designs.

is an integral part of the design and development process.

Materials required for sketching Sketching paper(Graph paper) Lead pencils and erasers Trigonometry set (compass, triangles and ruler) Templates (circles, curves)

Manual Drafting

is created on a paper or polyester film using manual drawing instruments and equipment.

Instruments used Drawing board and T-square or Drafting machine Compass set squares ( 45, 30-60) Protractor Lead pencils Eraser

Widely replaced by CADD in industry

Fig. 1 Manual drafting equipments

Fig. 1 Manual drafting equipments cont’d

Computer-Aided Drafting/Drawing

includes 2D projections and 3D solid modelling.

Some of popular software used for drawing and design of products are: AutoCAD and Inventor (Autodesk, Inc.). CATIA (Dassault Systems) MicroStation (Bentley Systems, Inc.) SolidWorks (SolidWorks Corporation, InterCAD) Solid Edge (UGS, The PLM Company) ArchiCAD Design / Building Series (GraphiSoft)

Drawing Standards

Importance of drawing standardsISO standardAustralian Standard related to engineering

drawing:

Basics of Engineering Drawing

Drawing sheets

Sizes: Factors that affect the selection of drawing sheets size

includes: the complexity of drawing, amount of information contained and the drawing equipment.Table 1: Dimensions of preferred sheets

Layout

Fig 2. Layout of a drawing sheet for detail drawing

Layout

Fig 3. Layout of a drawing sheet for assembly drawing

Borders/Frames

The drawing area on a drawing sheet is enclosed by a border (frame).

Borders/Frames

Table 2: Dimensions for drawing frames and margins

Elements of a drawing sheet

1. Title BlockIts recommended position is in the lower right-

hand corner. It is also allowed to be placed in the upper-right

hand corner if required. The contents of a title block include

drawing identification, company name, confidential statement, sheet size, scale, drafter and engineer’s names, and history of construction and revisions etc.

Recommended dimensions of title blocks

Fig 4. Title blocks for various size sheets

LOCATION INFORMATION

A Name of company, e.g. Curtin University, ABC Engineering, etc.

B Title of drawing, e.g. Crank shaft, bearing pedestal etc.

C Drawing identification number

D Information regarding drawing preparation, e.g. names / signatures of drafter, checker and approver, etc.

E Code identification number of the design authority (if needed)

F Drawing sheet size

G Scale of drawing, e.g. SCALE 1:1, SCALE 1:2, SCALE 5:1, etc

H Miscellaneous information

…. More blocks can be added for general information, such as tolerancing and finishing notes

Table 3: Location of contents of a title block

Elements of a drawing sheet

2. System of Projection: Method of project must be shown in a prominent

position. It could be an appropriate projection symbol or

words .

Fig 5: Method of projection a) third angle projection, b) first angle projection

a b

Elements of a drawing sheet

3. Prohibition of Scaling: Scaling dimensions directly from a drawing is extremely dangerous

and must be prohibited using the phrase “DO NOT SCALE”.

4. Dimensional Units: The correct dimensional units must be indicated on a drawing. For

metric units, this is done by including the phrase “ALL DIMENSIONS IN MILLIMETRES”.

5. Drafting Standard: Conformance to the particular edition of a drafting standard should

be shown. For example, DRAFTING STANDARD AS 1100 – 1992

6. Other Information: Where it is appropriate, space in the area to the left of title block

should be provided for other relevant information such as tolerance notes, heat treatment and machining requirements etc.

Drawing Scale

Why scale?Types of scale1. Full Size:

In this case, the drawing size is equal to the size of the object. This scale is indicated as SCALE 1:1.

2. Reduction Ratios (Scaling down): In this case, the drawing size is smaller than the size of

the object.

3. Enlargement Ratios (Scaling up): In this case, the drawing size is greater than the size of

the object. For small objects, drawn using large scales, a full-size view of the object should be added to the drawing.

Drawing Scale

recommended scales for mechanical engineering drawings are shown below.

Table 4: Engineering drawing scales

Full size and enlargement ratios

5:1 2:1 10:11:1

Reduction ratios

1:2 1:2.5 1:5 1:10

1:20 1:25 1:50 1:100

1:200 1:250 1:500 1:1 000

1:2 000 1:2 500 1:5 000 1:10 000

1:25 000 1:50 000 1:100 000

Drawing Scale

Indicating scale on drawingThe scale of a drawing should be shown by:

Block or graduated scale The “SCALE” word followed by the ratio. For

example, SCALE 1:100. “NOT TO SCALE” words in or near the title block or a

diagonal line through the space reserved for the indication of scale ratio specifies that the drawing is not drawn to any consistent scale.

NOTE: Regardless of the scale used, the actual values of dimensions are indicated on the drawing.

Line styles and application

Lines on a drawing illustrate the shape and size of objects that will later become real parts.

A particular line type is defined by two essential features shape of the line, and thickness (or line weight) of the line.

Fig 6: Commonly used line types

Note that:• Lines on drawing sheets

should be clear, uniform in thickness, dark and must be of a quality that reproduces easily.

• There should be no variation in darkness

Fig 7: Definition and application of the standard line types

Fig 7: Definition and application of the standard line types cont’d

Line styles and application cont’d

Notes on definition and application of the standard line types (Fig 7):

1. It is desired to restrict line thickness to two on any one drawing. A medium thickness line may be used by some drafting disciplines.

2. It is recommended that only one thickness of dashed line be used.

3. Proportion of spaces is as specified for type G. Order of Precedence

Visible outlines and edges Hidden lines Cutting plane lines Centre line Centroidal lines Projection lines

Fig 8: Application of Line types

Fig 9: Poor definition of line types

Letters and Numbers

Letters and numbers are used to represent notes, dimensions, and specifications, which can not be represented graphically.

According to AS 1100.101, the basic form of letters and characters on a drawing should be similar to either Gothic or ISO Type B character sets.

Upper case letters should be used except for conventional applications such as mm, kg etc.

Only one style of characters should be used through a drawing

Vertical characters should be used for titles, drawing and reference numbers

Fig 10: Lettering and numerals suggested by Standards Australia

References: Lecture Note- week 1 Fundamentals of Engineering

Drawing