1. Layouts and Lettering
Chapter 2

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

3. 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

4. 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

5. 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

6. Types of Projection

7. 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

8. 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

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

10. 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

11. Types of Projection

12. Types of Projection

13. 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

14. 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

15. 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

17. 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

18. Good and Poor Line Technique

19. 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

20. 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)

21. 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

22. 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

23. Scales
Scales are measuring tools used to quickly enlarge or reduce drawing measurements
Types of scales include:
Metric
Engineers’
Decimal
Mechanical engineers’
Architects’

24. 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

25. 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

26. 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

27. 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

28. 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

29. 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

30. Standard Sheet Sizes

31. Standard Layout Elements
Margins and borders
Zones
Typical letter sizes
Title block

32. 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