chapter 2

Layouts and LetteringChapter 2

*Technical Drawing 13th EditionGiesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart 2009 Pearson Education, Upper Saddle River, NJ 07458.All Rights Reserved.

ObjectivesIdentify six types of technical drawings based on the projection system they useIdentify the line patterns used in technical drawings and describe how they are usedRead and measure with the architects scale, engineers scale, and metric scale


Objectives (cont.)Identify standard drawing media and sheet sizesAdd lettering to a sketchFill in a standard title block with the appropriate informationLay out a drawing sheet


Understanding ProjectionsBehind every 2D drawing of an object is a space relationship involving the object and three imagined things:The observers eye or station pointThe plane of projectionThe projectorsAlso called visual rays or lines of sight


Types of ProjectionThere are two main types of projectionPerspective projection the projectors come together at the station pointPerspective drawings represent objects as we see them Parallel projection the projectors are parallel


Types ofProjection


Types of ProjectionOrthographic projections are a type of parallel projectionOrthographic (right angle) projections have parallel projectors that are perpendicular to the plane of projectionIn orthographic projection objects can be presented at true size or scaled at a proportion of their true size


Types of ProjectionOblique projection when projectors are parallel to each other but are at an angle other than 90 degrees to the plane of projection


Types of ProjectionTechnical drawings of 3D objects usually use one of four standard types of projectionMultiview Axonometric (isometric)ObliquePerspective


Types of ProjectionMultiview projection shows one or more necessary views of an objectThere are two systems used to arrange the views:Third angle projectionFirst angle projectionAxonometric, oblique, and perspective sketches show objects pictorially


Types ofProjection


Types of Projection


Drawing VocabularyDrawing lines projected line drawings use specific line patterns to represent object featuresLettering the shapes of letters are described as part of drawing standardsMeasurement systems both the metric system and U.S. customary units may be used


Drawing VocabularyScale to clearly convey important information about particularly large or small objects, appropriate sheet size and scale must be selectedTitle 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 styleAll 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 linesFreehand lines show freedom and variety but, aside from construction lines, should be dark and clean


Good and Poor Line Technique


Measurement SystemsU.S. Customary UnitsBased on inch-foot and yard measurementsDrawings with these units still follow ANSI/ASME standardsDrawing units must be clearly stated on the drawing


Measurement SystemsThe metric systemThis is the International System of Units, commonly referred to as SIThe 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 ScaleDrawing scale is the reduction or enlargement of the size of a drawn object relative to the real objectScale is often determined on the size of drawing sheet usedScale is stated as a ratio of the number of drawing units to the number of actual units


Specifying the Scale on a DrawingThere are several acceptable methods to note scale on a drawingFor example, a part thats shown on the paper at half its actual size, the scale may be listed in one of these ways:SCALE 1:2SCALE SCALE .5


ScalesScales are measuring tools used to quickly enlarge or reduce drawing measurementsTypes of scales include:MetricEngineers DecimalMechanical engineersArchitects


LetteringLettered text is often necessary to describe an object or to provide detailed specificationsLettering should be legible, easy to create, and use appropriate styles


LetteringThe creation of neat freehand lettering has three necessary aspects:Knowing the proportions and forms of the lettersSpacing of letters and words for legibilityPractice


LetteringCAD drawings typically use a Gothic lettering style but often use a Roman style for titlesWhen 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 ToolMost technical drawings are created using CADAdvantages of CAD include:AccuracySpeedThe ability to present spatial and visual information in a variety of ways


The Computer as a Drafting ToolThe advantages of CAD do not eliminate the need for drawings to be easily and accurately interpretedThe same general concepts and drafting standards apply to CAD as to drawings created by hand


Sketching and Drawing MediaThere are many media available for sketching and drawing purposes including:Sketch pads and notebooksGrid paperIsometric paperPolyester filmCoated sheets of aluminum


Standard Sheet Sizes


Standard Layout ElementsMargins and bordersZonesTypical letter sizesTitle block


Planning Your Drawing or SketchWhen laying out a drawing sheet you will need to consider:Size and scale of the objectSheet sizeMeasurement systemSpace necessary for notes and title block

chapter 2

Documents

Transcript of chapter 2