OBJECTIVES 1. Identify six types of technical drawings based on the projection system they use. 2. Identify the line patterns used in technical drawings and describe how they are used. 3. Read and measure with the architects’ scale, engineers’ scale, and metric scale. 4. Identify standard drawing media and sheet sizes. 5. Add lettering to a sketch. 6. Fill in a standard title block
PROJECTIONS Behind every 2D drawing of an object is a space relationship involving the object and three “imagined” things: 1. The observer’s eye, or station point 2. The plane of projection 3. The projectors (also called visual rays or lines of sight ). Perspective Projection Parallel Projection
Types of Projections There are two main types of projection: perspective and parallel . These are broken down into subtypes, as shown below:
ALPHABET OF LINES Thick and Thin Drawing Lines Freehand line technique Line styles
FREEHAND LINES The main difference between an instrument or CAD drawing and a freehand sketch is in the appearance of the lines. A good freehand line is not expected to be precisely straight or exactly uniform, as is a CAD or instrument-drawn line. Freehand lines show freedom and variety. Freehand construction lines are very light, rough lines. All other lines should be dark and clean.
MEASUREMENT SYSTEMS U.S. Customary Units The Metric System Dual-Dimensioned
DRAWING SCALE Drawing scale is the reduction or enlargement of the drawn object relative to the real object Reduced and Enlarged Scale. Many drawings must be shown at reduced scale for the object to fit on the paper.
SPECIFYING THE SCALE ON A DRAWING List the predominant drawing scale in the title block. (Courtesy of Dynojet Research, Inc.) For a part that is shown on the paper at half its actual size, the scale is listed in one of these three ways: SCALE: 1:2 SCALE: 1/2 SCALE: .5 Architectural drawings list the scale based on the number of fractions of an inch on the drawing that represent one foot on the actual object. Example: SCALE: 1/8" 1'
SCALES Scales are measuring tools used to quickly enlarge or reduce Drawing measurements. Types of Scales