Layouts and Lettering Chapter 2

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 of Projection

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 of Projection

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