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CADD PRIMER
Chapter 3: The Drawing Tools
 Contents
About this Chapter
Key Terms in this Chapter
The Drawing Tools of CADD
Using Line Types
Drawing Multiple Parallel Lines
Drawing Flexible Curves
  • Drawing Arcs and Circles
  • Center Point and Radius
  • 3 Points
  • Radius and Rotation Angle
  • 2 Points
  • 2 Tangents and a Point
  • 3 Tangents
Drawing Ellipses and Elliptical Arcs
  • Length and Width
  • Axis and Rotation Angle
Adding Text to Drawings
  • Text Height
  • Height to Width Ratio and Inclination of Letters
  • Special Effects 3-14
  • Alignment of Text (Justification)
  • Text Fonts
Defining a Text Style

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Drawing Dimensions
  • Drawing Horizontal and Vertical Dimensions
  • Dimensioning from a Baseline
  • Dimensioning Arcs and Circles
  • Drawing Dimensions Parallel to an Object
  • Dimensioning Angles
Writing Dimensions with Different Units
Setting Dimension Styles
Adding Hatch Patterns to Drawings
Drawing Symbols
Drawing Arrows
The Artistic Side of CADD
AutoCAD, MicroStation and Cadkey Terms
About this Chapter This chapter focuses on the two-dimensional drawing functions of CADD. It describes in detail how to draw each element of a drawing. You will learn the unique characteristics of different drawing elements that make them suitable for specific drawing tasks.

In this chapter you will learn the following:

    • How to create line types such as dotted lines, dashed lines, multi-lines and splines.
    • How to draw arcs, circles and ellipses.
    • How to write text and dimensions with different styles and how to control various aspects associated with them such as size, fonts and units.
    • How to make drawings presentable using drawing annotations such as symbols, arrows, borders and hatching patterns.
Key Terms in this Chapter
 
Term
Description
Associative dimensions A mode of dimensioning that automatically updates dimension values when the dimension size is changed.
Benchmark A reference point from where all distances are measured.
Spline A flexible curve that can be drawn to fit any shape.
Hatch patterns Ready-made patterns that can be added to a specified area in a drawing.
Justification The alignment of text strings in a specific direction such as to the right, left, or center. 
Polyline A string of lines that may contain a number of line segments connected together.
Tangent A point on a circle that forms 90° angle between the center point of the circle and another point outside the circle. 

The Drawing Tools of CADD AutoCAD Forum

The following are the basic drawing tools found in a CADD program:

    • Line types
    • Multiple parallel lines
    • Flexible curves
    • Arcs and circles
    • Ellipses and elliptical arcs
    • Text
    • Dimensions
    • Hatch patterns
    • Polygons
    • Arrows


Using Line Types

There are a number of line types available in CADD that can be used to enhance drawings. There are continuous lines, dotted lines, center lines, construction lines, etc. Fig. 3.1 shows some examples of common line types used in architectural and engineering drawings.

CADD enables you to follow both geometrical and engineering drawing standards. You can use line types to represent different annotations in a drawing. For example, an engineer can use line types to differentiate between engineering services in a building plan. One line type can be used to show power supply lines, while the others to show telephone lines, water supply lines and plumbing lines.

CADD is preset to draw continuous lines. When you enter the line command and indicate a starting point and end point, a continuous line is drawn. If you want to draw with another line type, you need to set that line type as the current line type. Thereafter, all the lines are drawn with the newly selected line type.

Note:

You can change the line type of an existing line using CADD's editfunctions. Some people prefer to first draw everything with one line typeand later change line types as needed; others prefer to draw everythingwith the right line type the first time.

Drawing Multiple Parallel Lines
CADD allows you draw parallel lines simultaneously just by indicating astarting point and an end point. These lines can be used to draw somethingwith heavy lines or double lines. For example, they can be used to draw thewalls of a building plan, roads of a site map, or for any otherpresentation that requires parallel lines.

Most programs allow you to define a style for multiple parallel lines. Youcan specify how many parallel lines you need, at what distance and if theyare to be filled with a pattern or solid fill.

A number of add-on programs use multiple lines to represent specificdrawing features. For example, an architectural program has a specialfunction called "wall'. When you use this option, it automatically drawsparallel lines representing walls of specified style and thickness.

Note:

Multiple lines are a unified entity. Even though double lines are drawn,they are treated as one line. You cannot erase or edit one line separately.However, there are functions available that can break the entities apart.

Drawing Flexible Curves
CADD allows you to draw flexible curves (often called splines) that can beused to draw almost any shape. They can be used to create the smooth curvesof a sculpture, contours of a landscape plan or roads and boundaries of amap.

To draw a flexible curve, you need to indicate the points through which thecurve will pass. A uniform curve is drawn passing through the indicatedpoints. The sharpness of the curves, the roughness of the lines and thethickness can be controlled through the use of related commands.

Note:

The computer needs a lot of memory to draw flexible curves; they should beused only when necessary.

Drawing Arcs and Circles
CADD provides many ways to draw arcs and circles. There are a number ofadvanced techniques available for drawing arcs and circles, which cansimplify many geometrical drawing problems. You can draw an arc byspecifying circumference and radius, radius and rotation angle, chordlength and radius, etc.

Arcs are drawn so accurately that a number of engineering problems can besolved graphically rather than mathematically. Suppose you need to measurethe circumference of an arc, just select that arc and the exact value isdisplayed.

The following are basic methods for drawing arcs and circles:
(These are essentially the same methods you learn in a geometry class.However, when drawing with CADD the approach is a little different.)

  • Center point and radius
  • 3 points
  • Angle and radius
  • 2 points
  • 2 tangents and a point
  • 3 tangents
  • Note: The above topics are described in detail in CADD PRIMER.
    Drawing Ellipses and Elliptical Arcs
    Ellipses are much easier to draw with CADD than on a drawing board. On adrawing board, you need to find the right size template or draw a series ofarcs individually to draw an ellipse. With CADD, all you need to do isspecify the size of the ellipse.

    The following are two basic methods for drawing ellipses:

  • Length and width
  • Axis and rotation angle
  • Length and Width

    An ellipse has two axes: a major axis and a minor axis (Fig. 3.6). Themajor axis determines the length of the ellipse and the minor axisdetermines the width.

    To draw an ellipse you need to specify length and width, i.e., major axisand minor axis. You can enter the values numerically or by indicatingpoints in the drawing area. When you need to draw an ellipse rotated at anangle, you can indicate the axis rotated at an angle. (Fig. 3.6.) To drawan elliptical arc, enter the starting point and the end point of the ellipse in addition to indicating the axes.

    Axis and Rotation Angle

    When a circle is viewed at an angle, it takes on an elliptical shape. CADDuses the same principle to draw an ellipse. It takes a circle and rotatesit into 3D space around one of the axes. As a result, the width of thecircle is reduced and an ellipse is drawn (Fig. 3.7).

    To draw an ellipse, you need to specify the length of the ellipse (majoraxis) and the rotation angle. The computer automatically calculates itswidth and draws an ellipse.

    Note:

    In advanced engineering systems, a number of additional methods for drawingelliptical arcs are available. These methods enable you to draw a varietyof elliptical shapes, including a parabola and a hyperbola.

    Adding Text to Drawings
    CADD allows you to add fine lettering to your drawings. You can use text towrite notes, specifications and to describe the components of a drawing.Text created with CADD is neat, stylish and can be easily edited. Typingskills are helpful if you intend to write a lot of text.

    Writing text with CADD is as simple as typing it on the keyboard. You canlocate it anywhere on the drawing, write it as big or as small as you likeand choose from a number of available fonts.

    Note:

    When large amounts of text are added to drawings, it slows down the screendisplays. Many programs provide options to temporarily turn off text or todisplay text outlines only. This feature helps save computer memory andspeeds up the display of screen images. The text can be turned back onwhenever needed.

    The following are the basic factors that control the appearance of text:
    (The exact terms and procedures used vary from one program to another.)

    • Text height
    • Height to width ratio and inclination of letters
    • Special effects
    • Alignment of text (justification)
    • Text fonts

    Note: The above topics are described in detail in CADD PRIMER.

    Important Tips:

    The fonts used in a drawing must be supported by the printer or plotterused for printing the drawing. You may want to do a test plot before usingspecific fonts in a drawing.

    When you need to send drawings electronically, make sure to include anyspecial fonts you might have used in the drawing. Otherwise, the recipientmay not be able to open the drawings.

    You can change the appearance of text using the editing functions ofCADD. You can change the height, width, inclination, rotation, spacing,fonts, justification, etc., as needed.

     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
    Note: CADD PRIMER is illustrated with more than 100 diagrams. The above diagram is an example from CADD PRIMER showing line types used in CAD.

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