Lockhart begins with instructions for using commands and techniques. In each lesson, the author provides step-by-step instructions with frequent illustrations showing exactly what appears on the AutoCAD screen. Later, individual steps are no longer provided, and readers are asked to apply what they've learned by completing sequences on their own. Carefully developed pedagogy reinforces this cumulative-learning approach and supports readers in becoming skilled AutoCAD users.
These tutorials take you from basics, such as parts of the screen and simple command entry, all the way through customizing your AutoCAD toolbars and creating your own commands. In 15 clear and comprehensive sessions, author Shawna Lockhart guides readers through all the important commands and techniques in AutoCAD As you progress through the step-by-step tutorials you apply what you have learned by completing familiar sequences on your own.
Frequent illustrations clearly depict what you see on your screen to help you in following the steps outlined. Carefully developed pedagogy reinforces this cumulative-learning approach, and support readers in becoming skilled AutoCAD users. 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. Defining Positions In AutoCAD, there are five methods for specifying the locations of points when we create planar geometric entities. The Guide Plate We will next create a mechanical design using the different coordinate entry methods. The rule for creating CAD designs and drawings is that they should be created at full size using real-world units.
The CAD database contains all the definitions of the geometric entities and the design is considered as a virtual, full-sized object. Only when a printer or plotter transfers the CAD design to paper is the design scaled to fit on a sheet. The tedious task of determining a scale factor so that the design will fit on a sheet of paper is taken care of by the CAD system.
This allows the designers and CAD operators to concentrate their attention on the more important issues — the design. Select the Line command icon in the Draw toolbar. In the command prompt area, we will locate the starting point of our design at the origin of the world coordinate system.
We will create a horizontal line by entering the absolute coordinates of the second point. Let us adjust the view of the line by using the Pan Realtime command. Click on the Pan Realtime icon in the Standard toolbar area. The icon is the picture of a hand with four arrows. This function acts as if you are using a video camera. Move the cursor, which appears as a hand inside the graphics window, near the center of the drawing window, then push down the left-mouse-button and drag the display toward the right and top side until we can see the sketched line.
Notice the scroll bars can also be used to adjust viewing of the display. Press the [Esc] key to exit the Pan command. We will create a vertical line by using the relative rectangular coordinates entry method, relative to the last point we specified:. We can mix any of the entry methods in positioning the locations of the endpoints. Create the next line by picking the location, world coordinates 8,2. We will next use the relative polar coordinates entry method, relative to the last point we specified:.
Using the relative rectangular coordinates entry method to create the next line, we can imagine a reference coordinate system aligned at the previous Reference Coordinate System point. Coordinates are measured aligned at the previous point along the two reference axes.
Move the cursor directly to the left of the last point and use the direct distance entry technique by entering 6. For the last segment of the sketch, we can use the Close option to connect back to the starting point.
Inside the graphics window, right-mouse-click and a popup menu appears on the screen. Select Close with the left-mouse-button to connect back to the starting point and end the Line command. Besides using the Draw toolbar, we can also select the different Draw commands through the pull-down menus. AutoCAD expects us to identify the location of a point or enter an option.
We can use any of the four coordinate entry methods to identify the desired location. We will enter the world coordinates 2. Inside the graphics window, right-mouse-click to bring up the popup option menu. Pick Repeat Center, Diameter with the left- mouse-button in the popup menu to repeat the last command. Using the relative rectangular coordinates entry method, relative to the center-point coordinates of the first circle, we specify the location as 2.
The default option for the Circle command in AutoCAD is to specify the radius and the last radius used is also displayed in brackets. Select the folder to store the file. Pick Save in the Save Drawing As dialog box to accept the selections and save the file. Questions: 1. What are the advantages and disadvantages of using CAD systems to create engineering drawings? Schroff Development Corporation www.
Introduction As illustrated in the previous chapters, there are no surfaces in a wireframe model; it consists only of points, lines, and curves that describe the edges of the object. Surface modeling was developed to provide the surface information that is missing in wireframe modeling.
Essentially, defining the skin of a design creates a surface model. Although it is possible to create a surface model without using a wireframe model, in most cases it is much easier to create a surface model on top of a wireframe model.
In surface modeling, a wireframe model can be used to provide information about the edges and corners so that the desired faces can be easily positioned and placed. Surface modeling is more sophisticated than wireframe modeling in that surface modelers define not only the edges of 3D objects, but also the surfaces.
Surface modeling provides hiding, shading, and rendering capabilities that are not available in wireframe modeling. Surface models do not provide the physical properties that solid models provide, such as mass, weight, center of gravity, and so on. The AutoCAD surface modeler defines faceted surfaces using a filled polygon. The created faces of surface models are only planar, which means the surface models can only have approximate curved surfaces.
It is important to note that the AutoCAD surface modeler does not create true curved surfaces. To differentiate these two types of surfaces, faceted surfaces are called meshes in AutoCAD. Because of the use of faceted approximation on true curved surfaces, the computer requirements of most faceted surface modelers are typically much less than that of solid modelers. Faceted surface modeling usually provides reasonably good representations of 3D designs with fast rendering and shading capabilities.
Faceted surface models are also useful for creating geometry with unusual surface patterns, such as a 3D topographical model of mountainous terrain. The three commands were developed parallel to the historical development of the different types of computer modelers. Used mostly to fill an area in the sketch plane of the current UCS. This type of surface is not a true 3D surface. This is the type of surface developed primarily for creating faceted surface models.
This command creates the most flexible and the most complicated type of surface available in AutoCAD. This command was developed to allow manipulation of 2D surfaces using one of the solid modeling construction techniques, namely, the Constructive Solid Geometry method. Although all three commands can be used to create planar surfaces, the resulting surfaces are not equal.
In fact, the three commands are developed for specific tasks in mind. The 2D Solid command is mostly used in 2D drawings to create 2D filled area and the Region command is designed so that general 2D shapes can be easily transformed into solid models. The 3D Face command is the only one that is designed specifically for surface modeling and therefore it is the most suitable for such tasks.
The use of the 2D Solid and Region commands in 3D surface modeling can be somewhat awkward and at times very difficult. Note that the use of the Region command will be focused on in the solid modeling chapters of this text. As one can imagine, sketching each surface manually can be very time consuming and tedious. AutoCAD also provides additional tools for surface modeling, such as Predefined surfaces, Tabulated surfaces, Ruled surfaces and Revolved surfaces.
These tools are basically automated procedures, which can be used to define and create multiple copies of planar surfaces in specific directions.
The principles and concepts used by these tools are also used in creating solid models, which are covered in chapter six through chapter eight of this text. You are encouraged to re-examine these commands after you have finished the solid modeling chapters. In this chapter, the general procedures to create surface models are illustrated. The use of the 2D Solid and 3D Face commands are illustrated and differences discussed. We will also demonstrate the use of the more advanced surface modeling tools.
Two wireframe models, which were created in the previous chapters, will be converted into surface models. Click on the V-block. Use the Browse option to locate the file if it is not displayed. Move the cursor to the Standard toolbar area and right- click on any icon of the Standard toolbar to display a list of toolbar menu groups.
Select Surfaces, with the left-mouse-button, to display the Surfaces toolbar on the screen. On your own, move the cursor on top of the different icons and read the brief description of the individual commands in the help- line area.
Pick the lower-right corner of the front face of the wireframe model as shown. Pick the adjacent corner toward the right side of the model as shown. Pick the right corner of the inclined plane as shown. Place the first corner-point of the 2D solid at the origin of the new UCS. Pick the bottom-right corner of the inclined plane as shown.
Pick the corner directly above the origin of the UCS as shown. This seemly strange way of specifying the third corner was established when the 2D Solid command was first introduced back in the mids.
Pick the corner directly above the second point we selected as shown in the figure. Inside the graphics window, right- mouse-click once to end the 2D Solid command.
Note that in the above steps, we could accept the three-sided polygon after defining the third corner. Using the Shade Toolbar 1. Move the cursor to the Standard toolbar area and right-click on any icon of the Standard toolbar to display a list of toolbar menu groups. Select Shade, with the left-mouse-button, to display the Shade toolbar on the screen.
Shading options 2D Wireframe 3D Wireframe. Linetypes and lineweights are visible with this option. Note that this is the default AutoCAD display mode. Displays a shaded 3D user coordinate system UCS icon. Note that linetypes and lineweights are not visible with this option.
The shaded objects appear flatter and less smooth than Gouraud Shaded objects. This mode generates an image that gives the objects a smooth and realistic appearance. The objects are flat shaded with the wireframe edges showing through. The objects are Gouraud shaded with the wireframe edges showing through. In the Shade toolbar, click on the Gouraud Shaded icon to display the shaded image of the model. There exists only one surface in our model. The surface was created with the 2D Solid command.
Inside the arcball, press down the left-mouse-button and drag it to rotate the model freely in 3D space. On your own, reset the display to the SE Isometric View before continuing to the next section. This option resets the UCS to align to the world coordinate system. The 3D Face command can be used to create true 3D planar surfaces by allowing the X, Y and Z coordinates of the corners to be selected independently of the current UCS.
The created polygon can be a three-sided or four- sided shape. This command is the primary construction tool for surface modeling in AutoCAD. Pick the lower-right corner of the vertical inclined face of the model as shown. Pick the adjacent corner above the previous selected corner of the vertical inclined face as shown. Pick the adjacent corner of the right-vertical face of the model as shown.
Pick the corner below the last selected corner as shown. Pick the back corner of the model as shown. Inside the graphics window, right-mouse-click to activate the option menu and select Enter with the left-mouse-button to end the 3D Face command. In the Shade toolbar, click on the Hidden icon to display the model with hidden lines removed.
Rotate the model in 3D space and examine the constructed surface model. For surfaces of irregular shape, the Invisible Edge option is available in conjunction with the 3D Face command.
Note that the Invisible Edge option cannot be applied to polygons created by the 2D Solid command. Pick the top-right corner of the model as shown. Pick the top-front corner of the model as shown. Pick the top corner of the model adjacent to the previously selected corner as shown. On your own, repeat the zigzagging pattern to define polygons until all corners of the inclined surface have been selected and additional polygons are created as shown in the figure.
Note that the last polygon we created is a three- sided polygon. Note that the edges of the polygons are displayed as shown in the above figure. Note that the edges of the polygons are not visible when a shaded command is performed.
Pick the three edges inside the inclined surface as shown. Inside the graphics window, right- mouse-click to activate the option menu and select Enter to end the Edge command. In the Select File window, pick the Locator file that was created in chapter three. Click on the New button to create new layers. Inside the graphics window, pre- select all entities by using the left- mouse-button to create a selection window enclosing all entities.
On the Object Properties toolbar, choose the Layer Control box with the left-mouse-button. AutoCAD creates these models by prompting the user to input specific dimensions for the desired models. For example, the length, width and height dimensions are required for the Box surface model. Predefined surface models. Pick a point that is toward the right of the Locator model. Specify length of Box: 4. Specify width of Box: 3.
Specify height of Box: 2. Note that the surfaces of the box are created automatically and all faces of the model are grouped together as a single object. The main difficulty, and disadvantage, of surface modeling is that the constructed surfaces cannot be easily modified. In AutoCAD, we can use the grip-editing option to resize the constructed faces.
Select any edge of the surface model and note that the entire model is selected. Inside the graphics window, right-mouse-click once to accept the selection and the faces are separated into individual objects. Select the front vertical face of the model by clicking on the inside of the front face as shown. Move the cursor to the left, along the top-edge of the model, of its current location as shown.
Left-mouse-click once to reposition the grip-point. Delete all surface models before proceeding to the next section. These commands allow us to quickly create and duplicate surfaces in specific manners. Advanced surface commands. The resulting mesh is a series of parallel polygons running along a specified path.
The default values are set to six, which means any curve will be approximated with six straight lines. On your own, adjust the display of the wireframe model so that the four vertical lines connecting the two circles are visible as shown.
Note that we can only erase parts of a circle. We will therefore erase a portion of the circle and then split the circle into two arcs. Select the top circle as shown. Note that the selected portion will be erased.
We can override the first point by choosing First point in the option menu. Right-mouse-click once and select First point in the option menu. Choose the top endpoint of the vertical line as shown.
We will next split the circle into two arcs using the Break command. To split an object, choose the same endpoint that was chosen as the first endpoint. Select Extend in the Modify toolbar. Note the Projection type is set to View, as shown in the prompt window. Select the right vertical edge to be the extending boundary as shown.
Inside the graphics window, right-mouse-click once to accept the selection. Pick the shorter arc near the right endpoint to extend the arc in that direction. Inside the graphics window, right- mouse-click once to display the option menu and select Enter to end the Extend command.
Set the Surface layer as the Current Layer by choosing the layer name in the Layer Control box as shown. Pick Tabulated Surface in the Surfaces toolbar as shown. Choose the upper arc as shown. Choose the vertical line near the top endpoint as shown.
Note that the endpoint of the line is used as a reference point to determine the direction of the polygon mesh. On your own, use the Orbit and Shaded commands to examine the constructed polygons. This is set by the SurfTab1 variable. We can adjust number of segments to use by typing the word, surftab1, at the command prompt. We can use two different objects to define the edges of the ruled surface: lines, points, arcs, circles, ellipses, elliptical arcs, polylines, or splines.
The two objects to be used as the rails of a ruled surface mesh must both be either open or closed. For open curves, AutoCAD starts construction of the ruled surface based on the locations of the specified points on the curves.
Choose the lower arc by clicking on the right side as shown. Choose the inside straight edge on the right side as shown. To hide the edges of the polygons, it is necessary to separate the polygon into individual entities. Select any edge of the ruled surface and notice that all six polygons are selected. Inside the graphics window, right-mouse-click once to accept the selection and the polygons are separated into individual objects. Select 2D Wireframe in the Shade toolbar to display the entities in wireframe mode.
Pick the five edges inside the ruled surface as shown. On your own, repeat the above steps and create another ruled surface as shown.
Hint: Use the Realtime Zoom function to assist the selection of the arc.
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