Layouts and Lettering Chapter 2. 2 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education,

Layouts and Lettering

Chapter 2

2Technical Drawing 13th EditionGiesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

All Rights Reserved.

Objectives

• Identify six types of technical drawings based on the projection system they use

• Identify the line patterns used in technical drawings and describe how they are used

• Read and measure with the architect’s scale, engineer’s scale, and metric scale




Objectives (cont.)

• Identify standard drawing media and sheet sizes

• Add lettering to a sketch• Fill in a standard title block with

the appropriate information• Lay out a drawing sheet




Understanding Projections

• Behind every 2D drawing of an object is a space relationship involving the object and three “imagined” things:• The observer’s eye or station point• The plane of projection• The projectors

• Also called visual rays or lines of sight




Types of Projection

• There are two main types of projection• Perspective projection – the

projectors come together at the station point• Perspective drawings represent objects

as we see them • Parallel projection – the projectors are

parallel




Types ofProjection




Types of Projection

• Orthographic projections are a type of parallel projection• Orthographic (right angle) projections

have parallel projectors that are perpendicular to the plane of projection

• In orthographic projection objects can be presented at true size or scaled at a proportion of their true size




Types of Projection

• Oblique projection – when projectors are parallel to each other but are at an angle other than 90 degrees to the plane of projection




Types of Projection

• Technical drawings of 3D objects usually use one of four standard types of projection• Multiview • Axonometric (isometric)• Oblique• Perspective




Types of Projection

• Multiview projection – shows one or more necessary views of an object• There are two systems used to arrange

the views:• Third angle projection• First angle projection

• Axonometric, oblique, and perspective sketches show objects pictorially




Types ofProjection




Types of Projection




Drawing Vocabulary

• Drawing lines – projected line drawings use specific line patterns to represent object features

• Lettering – the shapes of letters are described as part of drawing standards

• Measurement systems – both the metric system and U.S. customary units may be used




Drawing Vocabulary

• Scale – to clearly convey important information about particularly large or small objects, appropriate sheet size and scale must be selected

• Title blocks – company information, drawing scale, sheet size and other information is included in a standard title block




Alphabet of Lines

• The meaning of each line on a technical drawing is indicated by its width and its particular line style

• All lines should be uniform in width and darkness







Freehand Lines

• The main difference between a CAD drawing and a freehand sketch is in the appearance of lines

• Freehand lines show freedom and variety but, aside from construction lines, should be dark and clean




Good and Poor Line Technique




Measurement Systems

• U.S. Customary Units• Based on inch-foot and yard

measurements• Drawings with these units still follow

ANSI/ASME standards• Drawing units must be clearly stated

on the drawing




Measurement Systems

• The metric system• This is the International System of

Units, commonly referred to as SI• The primary unit of measurement for

engineering drawings and design in the mechanical industries is the millimeter (mm)

• Secondary units are the meter (m) and kilometer (km)




Drawing Scale

• Drawing scale is the reduction or enlargement of the size of a drawn object relative to the real object• Scale is often determined on the size

of drawing sheet used• Scale is stated as a ratio of the

number of drawing units to the number of actual units




Specifying the Scale on a Drawing• There are several acceptable

methods to note scale on a drawing• For example, a part that’s shown on

the paper at half its actual size, the scale may be listed in one of these ways:• SCALE 1:2• SCALE ½• SCALE .5




Scales

• Scales are measuring tools used to quickly enlarge or reduce drawing measurements

• Types of scales include:• Metric• Engineers’ • Decimal• Mechanical engineers’• Architects’




Lettering

• Lettered text is often necessary to describe an object or to provide detailed specifications

• Lettering should be legible, easy to create, and use appropriate styles




Lettering

• The creation of neat freehand lettering has three necessary aspects:• Knowing the proportions and forms of

the letters• Spacing of letters and words for

legibility• Practice




Lettering

• CAD drawings typically use a Gothic lettering style but often use a Roman style for titles

• When lettering a CAD drawing, it is advisable to not use more than two fonts within the same drawing for clarity




The Computer as a Drafting Tool• Most technical drawings are

created using CAD• Advantages of CAD include:

• Accuracy• Speed• The ability to present spatial and

visual information in a variety of ways




The Computer as a Drafting Tool• The advantages of CAD do not

eliminate the need for drawings to be easily and accurately interpreted

• The same general concepts and drafting standards apply to CAD as to drawings created by hand




Sketching and Drawing Media• There are many media available

for sketching and drawing purposes including:• Sketch pads and notebooks• Grid paper• Isometric paper• Polyester film• Coated sheets of aluminum




Standard Sheet Sizes




Standard Layout Elements

• Margins and borders• Zones• Typical letter sizes• Title block




Planning Your Drawing or Sketch• When laying out a drawing sheet

you will need to consider:• Size and scale of the object• Sheet size• Measurement system• Space necessary for notes and title

block

Documents

Layouts and Lettering Chapter 2. 2 Technical Drawing 13 th Edition Giesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart © 2009 Pearson Education,