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Tipologia: Exercícios
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AutoCAD Certified User Examination Objectives Coverage
This table shows the pages on which the objectives of the Certified User Examination are covered in Chapter 1.
AutoCAD Fundamentals 1-
Learning to use a CAD system is similar to learning a new language. It is necessary to begin with the basic alphabet and learn how to use it correctly and effectively through practice. This will require learning some new concepts and skills as well as learning a different vocabulary. Today, the majority of the Mechanical CAD systems are capable of creating three-dimensional solid models. Nonetheless, all CAD systems create designs using basic geometric entities and many of the constructions used in technical designs are based upon two-dimensional planar geometry. The method and number of operations that are required to accomplish the basic planar constructions are different from one system to another.
In order to become effective and efficient in using a CAD system, we must learn to create geometric entities quickly and accurately. In learning to use a CAD system, lines and circles are the first two, and perhaps the most important two, geometric entities that one should master the skills of creating and modifying. Straight lines and circles are used in almost all technical designs. In examining the different types of planar geometric entities, the importance of lines and circles becomes obvious. Triangles and polygons are planar figures bounded by straight lines. Ellipses and splines can be constructed by connecting arcs with different radii. As one gains some experience in creating lines and circles, similar procedures can be applied to create other geometric entities. In this chapter, the different ways of creating lines and circles in AutoCAD 2015 are examined.
Once the program is loaded into memory, the AutoCAD 2015 main drawing screen will appear on the screen.
AutoCAD Fundamentals 1-
Every object we construct in a CAD system is measured in units. We should determine the system of units within the CAD system before creating the first geometric entities.
The AutoCAD Menu Bar contains multiple pull-down menus, where all of the AutoCAD commands can be accessed. Note that many of the menu items listed in the pull-down menus can also be accessed through the Quick Access toolbar and/or Ribbon panels.
1-6 AutoCAD 2015 Tutorial: 2D Fundamentals
Next, we will set up the Drawing Limits by entering a command in the command prompt area. Setting the Drawing Limits controls the extents of the display of the grid. It also serves as a visual reference that marks the working area. It can also be used to prevent construction outside the grid limits and as a plot option that defines an area to be plotted/printed. Note that this setting does not limit the region for geometry construction.
1-8 AutoCAD 2015 Tutorial: 2D Fundamentals
We will create a freehand sketch of a five- point star using the Line command. Do not be overly concerned with the actual size or accuracy of your freehand sketch. This exercise is to give you a feel for the AutoCAD 2015 user interface.
Coordinates of the graphics cursor
AutoCAD Fundamentals 1-
AutoCAD Fundamentals 1-
The GRID option creates a pattern of lines that extends over an area on the screen. Using the grid is similar to placing a sheet of grid paper under a drawing. The grid helps you align objects and visualize the distance between them. The grid is not displayed in the plotted drawing. The default grid spacing, which means the distance in between two lines on the screen, is 0.5 inches. We can see that the sketched horizontal line in the sketch is about 4 inches long.
1-12 AutoCAD 2015 Tutorial: 2D Fundamentals
The SNAP option controls an invisible rectangular grid that restricts cursor movement to specified intervals. When SNAP mode is on, the screen cursor and all input coordinates are snapped to the nearest point on the grid. The default snap interval is 0.5 inches, and aligned to the grid points on the screen.
1-14 AutoCAD 2015 Tutorial: 2D Fundamentals
Inside the graphics window, click once with the right-mouse- button to bring up the popup option menu.
AutoCAD 2015 offers many options to accomplish the same task. Throughout this text, we will emphasize the use of the AutoCAD Heads-up Design TM^ interface, which means we focus on the screen, not on the keyboard.
On your own, create a free-hand sketch of your choice using the Line command. Experiment with using the different commands we have discussed so far. Reset the status buttons so that only the GRID DISPLAY option is turned ON as shown.
Second corner
First corner
AutoCAD Fundamentals 1-
Designs and drawings created in a CAD system are usually defined and stored using sets of points in what is called world space. In most CAD systems, the world space is defined using a three-dimensional Cartesian coordinate system. Three mutually perpendicular axes usually referred to as the X-, Y-, and Z-axes, define this system. The intersection of the three coordinate axes forms a point called the origin. Any point in world space can then be defined as the distance from the origin in the X-, Y- and Z- directions. In most CAD systems, the directions of the arrows shown on the axes identify the positive sides of the coordinates.
A CAD file, which is the electronic version of the design, contains data that describes the entities created in the CAD system. Information such as the coordinate values in world space for all endpoints, center points, etc., along with the descriptions of the types of entities are all stored in the file. Knowing that AutoCAD stores designs by keeping coordinate data helps us understand the inputs required to create entities.
The icon near the bottom left corner of the default AutoCAD graphics window shows the positive X-direction and positive Y-direction of the coordinate system that is active. In AutoCAD, the coordinate system that is used to create entities is called the user coordinate system (UCS). By default, the user coordinate system is aligned to the world coordinate system ( WCS ). The world coordinate system is a coordinate system used by AutoCAD as the basis for defining all objects and other coordinate systems defined by the users. We can think of the origin of the world coordinate system as a fixed point being used as a reference for all measurements. The default orientation of the Z-axis can be considered as positive values in front of the monitor and negative values inside the monitor.
3D UCS icon
AutoCAD Fundamentals 1-
In a two-dimensional space, a point can be represented using different coordinate systems. The point can be located, using a Cartesian coordinate system , as X and Y units away from the origin. The same point can also be located using the polar coordinate system , as r and units away from the origin.
For planar geometry, the polar coordinate system is very useful for certain applications. In the polar coordinate system, points are defined in terms of a radial distance, r, from the origin and an angle between the direction of r and the positive X axis. The default system for measuring angles in AutoCAD 2015 defines positive angular values as counter-clockwise from the positive X-axis.
AutoCAD 2015 also allows us to use absolute and relative coordinates to quickly construct objects. Absolute coordinate values are measured from the current coordinate system's origin point. Relative coordinate values are specified in relation to previous coordinates.
Note that the coordinate display area can also be used as a toggle switch; each left- mouse-click will toggle the coordinate display on or off.
In AutoCAD 2015 , the absolute coordinates and the relative coordinates can be used in conjunction with the Cartesian and polar coordinate systems. By default, AutoCAD expects us to enter values in absolute Cartesian coordinates , distances measured from the current coordinate system's origin point. We can switch to using the relative coordinates by using the @ symbol. The @ symbol is used as the relative coordinates specifier , which means that we can specify the position of a point in relation to the previous point.
1-18 AutoCAD 2015 Tutorial: 2D Fundamentals
In AutoCAD, there are five methods for specifying the locations of points when we create planar geometric entities.
Interactive method : Use the cursor to select on the screen.
Absolute coordinates (Format: X,Y) : Type the X and Y coordinates to locate the point on the current coordinate system relative to the origin.
Relative rectangular coordinates (Format: @X,Y) : Type the X and Y coordinates relative to the last point.
Relative polar coordinates (Format: @Distance<angle) : Type a distance and angle relative to the last point.
Direct Distance entry technique : Specify a second point by first moving the cursor to indicate direction and then entering a distance.
