Mastering AutoCAD 2005 and AutoCAD LT 2005

This section presents some of the more common AutoCAD commands and shows you how to use them to complete a simple drawing. As you draw, watch the prompts and notice how your responses affect them. Also notice how you use existing drawing elements as reference points.

While drawing with AutoCAD, you create simple geometric forms to determine the basic shapes of objects, and you can then modify the shapes to fill in detail.

AutoCAD offers 14 basic drawing object types: lines, arcs, circles, text, traces, polylines, points, 3D Faces, ellipses, elliptical arcs, spline curves, solids, regions , and multiline text. All drawings are built on these objects. In addition, there are five 3D meshes, which are three-dimensional surfaces composed of 3D Faces. You are familiar with lines and arcs; these, along with circles, are the most commonly used objects. As you progress through the book, you will learn about the other objects and how they are used.

Locating an Object in Reference to Others

To define the toilet seat, you will use an ellipse. Use these steps:

1. Click the Ellipse tool in the Draw toolbar or type El . You can also choose Draw   Ellipse   Axis, End.

2. At the Specify axis endpoint of ellipse or [Arc/Center]: prompt, pick the midpoint of the bottom horizontal line of the rectangle. Do this by opening the Osnap pop-up menu and selecting Midpoint; then move the cursor toward the bottom line. (Remember, Shift+click the right mouse button to open the Osnap menu.) When you see the Midpoint Osnap marker on the line, click the left mouse button.

3. At the Specify other endpoint of axis: prompt, move the cursor down until the Polar Tracking readout lists 1 ¢ -10 ² < 270 °. Metric users should use a readout of 55.0000 < 270 °.

4. Pick this as the second axis endpoint.

5. At the Specify distance to other axis or [Rotation]: prompt, move the cursor horizontally from the center of the ellipse until the Polar Tracking readout lists 0 ¢ -8 ² < 180 °. Metric users should use a readout of 20.0000 < 180 °.

6. Pick this as the axis distance defining the width of the ellipse. Your drawing should look like Figure 3.3.

   Figure 3.3: The ellipse added to the tank

   Tip

   As you work with AutoCAD, you will eventually run into NURBS. NURBS stands for Non-Uniform Rational B-Splines ”a fancy term meaning that curved objects are based on accurate mathematical models. When you trim the ellipse in a later exercise, it becomes a NURBS curve known as a spline in AutoCAD . You'll learn more about polylines and spline curves in Chapter 13.

Getting a Closer Look

During the drawing process, you will often want to enlarge areas of a drawing to edit its objects. In Chapter 1, you saw how to use the Zoom capability for this purpose. Follow these steps to enlarge the view of the toilet:

1. Click the Zoom Window tool on the Standard toolbar or type Z W . You can also choose View   Zoom   Window.

2. At the Specify first corner: prompt, pick a point below and to the left of your drawing, at or near coordinate 5 ¢ -0 ² , 3 ¢ -6 ² . Metric users should use the coordinate of 150.0000,102.0000.

3. At the Specify opposite corner: prompt, pick a point above and to the right of the drawing, at or near coordinate 8 ¢ -3 ² , 6 ¢ -8 ² (246.0000,195.0000 for metric users).The toilet should be completely enclosed by the zoom window. To obtain this view, use the Zoom Window tool. You can also use the Zoom Realtime tool in conjunction with the Pan Realtime tool. The toilet enlarges to fill more of the screen (see Figure 3.4).

   Figure 3.4: A close-up of the toilet drawing

   Tip	To open the Zoom Realtime tool from the keyboard, type Z . If you have a mouse with a scroll wheel, you can place the cursor on the toilet and turn the wheel to zoom into the image.

Modifying an Object

Now let's see how editing commands are used to construct an object. To define the back edge of the seat, let's put a copy of the line defining the front of the toilet tank 3 ² (7 cm for metric users) toward the center of the ellipse:

1. Click the Copy Object tool in the Modify toolbar or type co . You can also choose Modify   Copy from the pull-down menu.

   Tip	You can also use the Grip Edit tools to make the copy. See Chapter 2 for more on grip editing.

2. At the Select objects: prompt, pick the horizontal line that touches the top of the ellipse. The line is highlighted. Press to confirm your selection.

3. At the Specify base point or displacement: prompt, pick a base point near the line. Then move the cursor down until the Polar Tracking readout lists 0 ¢ -3 ² < 270 ° or 7.0000 < 270 ° for metric users.

4. Pick this point then press to exit the Copy command. Your drawing should look like Figure 3.5.

   Figure 3.5: The line copied down

   Note	If you've used earlier versions of AutoCAD the Copy command no longer offers the Multiple option. Instead, Copy automatically offers multiple copies. Pressing exits the command.

Notice that the Copy command acts exactly like the Move command you used in Chapter 2, except that Copy does not alter the position of the objects you select.

You might be asking yourself if there is a set of standard architectural measurements for common items, such as the aforementioned toilet tank. Some items, such as doors and kitchen appliances, do have "standard"sizes that architects learn in the course of their professional training. In this particular example, the 3-inch offset is arbitrary because the toilet symbol is just that, a symbol representing a toilet and not necessarily an exact representation of one. When you see a toilet symbol in an architectural drawing, it's saying "put the toilet here."The actual brand of toilet is specified in the written specs that go with the drawings.

Trimming an Object

Now you must delete the part of the ellipse that is not needed. You will use the Trim command to trim off part of the ellipse:

1. First, turn off the Snap mode by pressing F9 or clicking the word Snap in the status bar. Snap mode can be a hindrance at this point in your editing session because it can keep you from picking the points you want. Snap mode forces the cursor to move to points at a given interval, so you will have difficulty selecting a point that doesn't fall exactly at one of those intervals.

2. Click the Trim tool in the Modify toolbar. You will see this prompt:

   Current settings: Projection=UCS Edge=None Select cutting edges ... Select objects:

3. Click the line you just created ”the one that crosses through the ellipse ”and press to finish your selection.

4. At the Select object to trim or shift-select to extend or [Project/Edge/Undo]: prompt, pick the topmost portion of the ellipse above the line. This trims the ellipse back to the line.

5. Press to exit the Trim command.

   Tip	By holding down the Shift key in step 4, you can change from trimming an object to extending an object. You'll learn about the Extend command in Chapter 13.

In step 2 of the preceding exercise, the Trim command produces two messages in the prompt. The first prompt, Select cutting edges: , tells you that you must first select objects to define the edge to which you want to trim an object. In step 4, you are again prompted to select objects, this time to select the objects to trim. Trim is one of a handful of AutoCAD commands that asks you to select two sets of objects: the first set defines a boundary, and the second is the set of objects you want to edit. The two sets of objects are not mutually exclusive. You can, for example, select the cutting-edge objects as objects to trim. The next exercise shows how this works.

First you will undo the trim you just did; then you will use the Trim command again in a slightly different way to finish off the toilet:

1. Click the Undo button in the Standard toolbar, or enter U at the command prompt. The top of the ellipse reappears.

2. Start the Trim tool again by clicking it in the Modify toolbar.

3. At the Select cutting edges: prompt, click the ellipse and the line crossing the ellipse (see the first image in Figure 3.6).

   Figure 3.6: Trimming the ellipse and the line

4. Press to finish your selection and move to the next step.

   Tip	These Trim options ”Project, Edge, and Undo ”are described in the section "The Trim Options" next in this chapter.

5. At the Select object to trim or [Project/Edge/Undo]: prompt, click the top portion of the ellipse, as you did in the previous exercise. The ellipse trims back.

6. Click a point near the left end of the trim line, past the ellipse. The line trims back to the ellipse.

7. Click the other end of the line. The right side of the line trims back to meet the ellipse. Your drawing should look like the second image in Figure 3.6.

8. Press to exit the Trim command.

9. Choose File   Save to save the file in its current state. You might want to get in the habit of doing this every 20 minutes.

Here you saw how the ellipse and the line are both used as trim objects, as well as the objects to be trimmed .

Exploring the Trim Options

AutoCAD offers three options for the Trim command: Edge, Project, and Undo. As described in the following paragraphs, these options give you a higher degree of control over how objects are trimmed.

Edge [E]     Enables you to trim an object to an apparent intersection, even if the cutting-edge object does not intersect the object to be trimmed (see the top of Figure 3.7). Edge offers two options: Extend and No Extend. You can also set these options by using the Edgemode system variable.

Figure 3.7: The Trim command's options

Project [P]     Useful when working on 3D drawings. It controls how AutoCAD trims objects that are not coplanar. Project offers three options: None, UCS, and View. The None option causes Trim to ignore objects that are on different planes so that only coplanar objects will be trimmed. If you choose UCS, the Trim command trims objects based on a Plan view of the current UCS and then disregards whether the objects are coplanar (see the middle of Figure 3.7). View is similar to UCS but uses the current view's "line of sight" to determine how non-coplanar objects are trimmed (see the bottom of Figure 3.7).

Undo [U]     Causes the last trimmed object to revert to its original length.

At times, you will want to select an object that is in close proximity to or lying underneath another object, and AutoCAD won't obey your mouse click. It's frustrating when you click the object you want to select, and AutoCAD selects the one next to it instead. To help you make your selections in these situations, AutoCAD provides Object Selection Cycling. To use it, hold down the Ctrl key while simultaneously clicking the object you want to select. If the wrong object is highlighted, press the left mouse button again (you do not need to hold down the Ctrl key for the second time), and the next object in close proximity is highlighted. If several objects are overlapping or close together, just continue to press the left mouse button until the correct object is highlighted. When the object you want is finally highlighted, press and continue with further selections.

You've just seen one way to construct the toilet. However, you can construct objects in many ways.

For example, you could have trimmed only the top of the ellipse, as you did in the first Trim exercise, and then used the Grips feature to move the endpoints of the line to meet the endpoints of the ellipse. As you become familiar with AutoCAD, you will start to develop your own ways of working, using the tools best suited to your style.

If you'd like to take a break, now would be a good time. You can exit AutoCAD and then come back to the Bath drawing file when you are ready to proceed.