Now that you have taken a quick tour of the AutoCAD and LT screens, you are ready to begin drawing. In this chapter, you will be introduced to a few basic commands used in drawing with AutoCAD and AutoCAD LT. To get you started, I will guide you through the process of drawing a box (see Figure 2.1).
Figure 2.1: The box to be drawn
You need to use only five or six commands to draw the box. First, you’ll become familiar with the Line command and how to make lines a specific length. Then I’ll go over the strategy for completing the box.
In traditional architectural drafting, lines were often drawn to extend slightly past their endpoints (see Figure 2.2). This is no longer done in CAD except for special effects.
Figure 2.2: The box drawn with overlapping lines
The Line command draws a line between locations on existing lines, between geometric figures, or between two points that you can choose anywhere within the drawing area. You can designate these points by clicking them on the screen, by entering the X and Y coordinates for each point in the Command window, or by entering distances and angles at the command line. After you draw the first segment of a line, you can end the command or draw another line segment from the end of the first one. You can continue to draw adjoining line segments for as long as you like. Let’s see how this works.
To be sure that you start with your drawing area set up the way it is set up for this book, choose File Close to close any open drawings. If multiple drawings are open, repeat the Close command for each drawing until you have no drawings open. Your drawing area will be gray and blank with no crosshair cursor, your toolbars will disappear except for five buttons on the Standard toolbar, and you will have only four drop-down menus.
Figure 2.3: The Draw and Modify toolbars docked on the left side of the drawing area, and all status bar buttons except Model turned off
Look at the bottom of the Command window and see how the Command: prompt has changed.
The prompt now tells you that the Line command is started (Command: _line) and that AutoCAD is waiting for you to designate the first point of the line (Specify first point:).
You can also start the Line command by choosing Draw Line or by typing L and pressing the Enter key.
It is now telling you that AutoCAD is waiting for you to designate the next point (Specify next point or [Undo]:).
Figure 2.4: Drawing several line segments
The Command: prompt has returned to the bottom line. This tells you that no command is running.
In this exercise, you used the left mouse button to select the Line button from the Draw toolbar and also to pick several points in the drawing area to make the line segments. You then pressed Enter () on the keyboard to end the Line command.
In the exercises that follow, the Enter symbol () will be used. When I say to “type” or “enter” something, it means to type the data that follows the word type or enter and then to press the Enter key (). For example, rather than writing “type L and press the Enter key,” I’ll write “type L.”
Try using the Line command again, but instead of picking points in the drawing area with the mouse as you did before, this time enter X and Y coordinates for each point from the keyboard. To see how, follow these steps:
You can also start the Erase command by typing e or by choosing Modify Erase.
Now start drawing lines again by following these steps:
The lines will be similar to those you drew previously, but this time you know where each point is located relative to the 0,0 point. In the drawing area, every point has an absolute X and Y coordinate. In steps 2 through 8, you entered the X and Y coordinates for each point. For a new drawing, such as this one, the origin (0,0 point) is in the lower-left corner of the drawing area, and all points in the drawing area have positive X and Y coordinates (see Figure 2.5).
Figure 2.5: The X and Y coordinates on the drawing area
Let’s explore how the cursor is related to the coordinates in the drawing.
In AutoCAD, you will see a readout for the Z coordinate as well, but you can ignore it for now because you will be working in only two dimensions for the majority of this book. The Z coordinate will always read 0 until you work in three dimensions (see the Appendix). AutoCAD LT does not have the readout for the Z coordinate.
The drawing area of a new drawing is preset to be 9 units high and 12–16 units wide, with the lower-left corner of the drawing at the coordinates 0,0.
For the moment, it doesn’t matter what measure of distance these units represent. I’ll address that topic in Chapter 3. And don’t worry about the four decimal places in the coordinate readout. The number of places is controlled by a setting you will learn about soon.
Once you understand the coordinate system used by AutoCAD, you can draw lines to any length and in any direction. Look at the box shown earlier in Figure 2.1. Because you know the dimensions, you can calculate, by adding and subtracting, the absolute coordinates for each vertex—the connecting point between two line segments—and then use the Line command to draw the shape by entering these coordinates from the keyboard. But AutoCAD offers you several tools for drawing this box much more easily. Two of these tools are the relative Cartesian and the relative polar coordinate systems.
When drawing lines, these systems use a set of new points based on the last point designated, rather than the 0,0 point of the drawing area. They are called “relative” coordinate systems because the coordinates used are relative to the last point specified. If the first point of a line is located at the coordinate 4,6, and you want the line to extend 8 units to the right, the coordinate that is relative to the first point is 8,0 (8 units in the positive X direction and 0 units in the positive Y direction), while the actual—or absolute—coordinate of the second point is 12,6.
The relative Cartesian coordinate system uses relative X and Y coordinates in just the manner shown, and the relative polar coordinate system relies on a distance and an angle relative to the last point specified. You will probably favor one system over the other, but you need to know both systems because at times, because of the information you have at hand, you will be able to use only one of the two. A limitation of this nature will be illustrated in Chapter 4.
When entering relative coordinates, you need to type an “at” symbol (@) before the coordinates. In the previous example, you would enter the relative Cartesian coordinates as @8,0. The @ lets AutoCAD know that the numbers following it represent coordinates that are relative to the last point designated.
Relative Cartesian Coordinates
The Cartesian system of coordinates, named after the philosopher Ren Descartes, who invented the X,Y coordinate system in the 1600s, uses a horizontal (X) and vertical (Y) component to locate a point relative to the 0,0 point. The relative Cartesian system uses the same components to locate the point relative to the last point picked, so it’s a way of telling AutoCAD how far left or right and up or down to extend a line or to move an object from the last point picked (see Figure 2.6). If the direction is to the left, the X coordinate will be negative. Similarly, if the direction is down, the Y coordinate will be negative. Use this system when you know the horizontal and vertical distances from point 1 to point 2. To enter data using this system, use this form: @x,y.
Figure 2.6: The relative Cartesian coordinate system
Relative Polar Coordinates
This system requires a known distance and direction from point 1 to point 2. Calculating the distance is straightforward: it’s always positive and is simply the distance away from point 1 that point 2 will be placed. The direction requires a convention for determining an angle. AutoCAD defines right (toward three o’clock) as the direction of the 0 angle. All other directions are determined from a counterclockwise rotation (see Figure 2.7). On your screen, up is 90, left is 180, down is 270, and a full circle is 360. To let AutoCAD know that you are entering an angle and not a relative Y coordinate, use the “less than” symbol (<) before the angle and after the distance. So in the previous example, to designate a point 8 units to the right of the first point, you would enter @8<0.
Figure 2.7: The relative polar coordinate system
Remember, use the relative polar coordinates method to draw a line from the first point when you know the distance and direction to its next point. Enter data using this form: @distance<angle.
Now that you have the basics, the following exercises will take you through the steps to draw the four lines that form the outline of the box using both relative coordinate systems.
To begin drawing the box, we’ll use the same drawing.
Figure 2.8: The first four lines of the box
To prepare to draw the box again, use the Erase command to erase the four lines you have just drawn.
You have been introduced to two methods of selecting lines to be erased: typing all and using the pickbox to select them. Throughout the book, you will be introduced to several other ways to select objects. The selection process is important in AutoCAD because you need to be able to quickly and precisely select objects.
Now draw the box again using the polar method by following these steps:
You can see from this exercise that you can use either method to draw a simple shape. When the shapes you are drawing get more complex and the amount of available information about the shapes varies from segment to segment, one of the two relative coordinate systems will turn out to be more appropriate. As you start drawing the floor plan of the cabin in Chapters 3 and 4, you will get more practice using these systems.
Some additional tools make the process of drawing simple, orthogonal lines like these much easier. I’ll introduce these tools in the following three chapters.
The next task is to create the lines that represent the inside walls of the box. Because they are all equidistant from the lines you have already drawn, the Offset command is the appropriate command to use. You will offset the existing lines 0.5 units to the inside.
The Offset command involves three steps:
Here’s how it works:
You can also start the Offset command by choosing Modify Offset or by typing o.
As important as it is to keep an eye on the Command window, some of the prompts may not make sense to you until you get used to them.
Note that the cursor has changed to a pickbox, and the prompt changes to say Select object to offset or <exit>:.
Figure 2.9: The first line to be offset is selected.
Figure 2.10: The first line is offset.
You have three more lines to offset.
Figure 2.11: Four lines have been offset.
You can cancel a command at any time by pressing Esc.
The offset distance stays set at the last distance you specify—0.5, in this case—until you change it.
This command is similar to the Line command in that it keeps running until it is stopped. With Offset, after the first offset, the prompts switch between Select object to offset or <exit>: and Specify point on side to offset: until you press to end the command.
The inside lines are now drawn, but to complete the box, you need to clean up the intersecting corners. To handle this task efficiently, we will use a new tool called the Fillet command.
Specifying Distances for the Offset Command
The prompt you see in the Command window after starting the Offset command is:
Specify offset distance or [Through] <1.0000>:
This prompt is actually describing several options for setting the offset distance.
As you get used to using Offset, you will find uses for each of these options.
The Fillet command lets you round off a corner formed by two lines. You control the radius of the curve, so if you set the curve’s radius to zero, the lines will form a sharp corner. In this way, you can clean up corners such as the ones formed by the lines inside the box.
You can also start the Fillet command by choosing Modify Fillet or by typing f.
The default fillet radius should be 0.0000 units. Like the Offset distance, the Fillet radius remains set at whatever length you specify until you change it.
Figure 2.12: Pick two lines to execute the Fillet command.
Figure 2.13: The first cleaned-up corner
Figure 2.14: The box with all corners cleaned up
Once a command has ended, you can restart it by pressing either or the spacebar or by right-clicking and choosing Repeat from the shortcut menu.
In most cases, you will get the same effect by pressing the spacebar as you get by pressing . The exception is when you are entering data in the Command window; in that case, pressing the spacebar just makes a space.
If you make a mistake and pick the wrong part of a line or the wrong line, press Esc to end the command and then type u. This will undo the effect of the last command.
Used together like this, the Offset and Fillet commands are a powerful combination of tools to lay out walls on a floor plan drawing. Because these commands are so important, let’s take a closer look at them to see how they work. Both commands are on the Modify toolbar or drop-down menu, both have the option to enter a numeric value or accept the current value—for offset distance and fillet radius—and both hold that value as the default until it is changed. However, the Offset command keeps running until you stop it, and the Fillet command stops after each use and must be restarted for multiple fillets. These two commands are probably the most frequently used tools in AutoCAD. You will learn about more of their uses in later chapters.
The Fillet command has a sister command, the Chamfer command, that is used to bevel corners with straight lines. When the distances for the Chamfer command are set to 0, you can use it to clean up corners in the same way that you use the Fillet command. Some users prefer to use Chamfer rather than Fillet because they don’t bevel corners but may at times use Fillet to round off corners. By using Chamfer to clean up corners, Fillet can have any radius and won’t have to constantly be reset to 0. You will develop your own preference.
The final step in completing the box (see Figure 2.1 earlier in this chapter) is to make an opening in the bottom wall. From the diagram, you can see that the opening is 2 units wide and set off from the right inside corner by 0.5 units. To make this opening, you will use the Offset command twice, changing the offset distance for each offset, to create marks for the opening.
Follow these steps to establish the precise position of the opening:
Figure 2.15: Offsetting the first line of the opening
Figure 2.16: Offsetting the second line of the opening
You now have two new lines indicating where the opening will be. You can use these lines to form the opening using the Extend and Trim commands.
The ”buttons” you have been clicking in this chapter are also referred to as “icons” and “tools.” When they are in dialog boxes or on the status bar, they have icons (little pictures) on them and actually look like buttons to push. When they are on the toolbars, they look like icons. But when you move the pointer arrow cursor onto one, it takes on the appearance of a button with an icon on it. I will use all three terms—button, icon, and tool— interchangeably in this book.
You use the Extend command to lengthen (extend) lines to meet other lines or geometric figures (called boundary edges). Executing the Extend command may be a little tricky at first until you see how it works. Once you understand it, however, it will become automatic. The command has two steps: first, you pick the boundary edge or edges, and second, you pick the lines you want to extend to meet those boundary edges. After selecting the boundary edges, you must press before you begin selecting lines to extend.
The bottom line says Select objects:, but in this case you need to observe the bottom two lines of text in order to know that AutoCAD is prompting you to select boundary edges.
Figure 2.17: Selecting a line to be a boundary edge
You can also start the Extend command by choosing Modify Extend from the Modify drop-down menu or by typing ex.
The Select Objects: prompt would be more useful if it said, “Select objects and press Enter when finished selecting objects.” But it doesn’t. You have to train yourself to press when you finish selecting objects in order to get out of selection mode and move on to the next step in the command.
Figure 2.18: The lines are extended to the boundary edge.
The final step is to trim away the horizontal lines to complete the opening. To do this, you use the Trim command. As with the Extend command, there are two steps. The first is to select reference lines—in this case, they’re called cutting edges because they determine the edge or edges to which a line is trimmed. The second step is to pick the lines that are to be trimmed.
You can also start the Trim command by choosing Modify Trim from the Modify drop-down menu or by typing tr.
Figure 2.19: Lines selected to be cutting edges
Figure 2.20: Lines selected to be trimmed
The opening is trimmed away (see Figure 2.21).
Figure 2.21: Lines are trimmed to make the opening.
If you trim the wrong line or wrong part of a line, you can click the Undo button on the Standard toolbar. This will undo the last trim without canceling the Trim command, and you can try again.
Now let’s remove the extra part of our trimming guide lines.
Figure 2.22: Lines picked to be cutting edges
Figure 2.23: Lines picked to be trimmed
Figure 2.24: The completed trim
Congratulations! You have just completed the first drawing project in this book and have covered all the tools in this chapter. These skills will be useful as you learn how to work on drawings for actual projects.
A valuable exercise at this time would be to draw this box two or three more times, until you can do it without the instructions. This will be a confidence-builder and will get you ready to take on new information in the next chapter, in which you will set up a drawing for a building.
The box you drew was 6 units by 5 units, but how big was it? You really don’t know at this time, because the units could represent any actual distance: inches, feet, meters, miles, and so on. Also, the box was positioned conveniently on the screen so you didn’t have any problem viewing it. What if you were drawing a building that was 200 feet long and 60 feet wide? In the next chapter, you will learn how to set up a drawing for a project of a specific size.
You can exit AutoCAD now without saving this drawing. To do so, choose File Exit. When the dialog box asks if you want to save changes, click No. Or you can leave AutoCAD open and go on to the following practice section or the next chapter.
Draw the following object shown in Figure 2.25.
Figure 2.25: Practice drawing
You can use the same tools and strategy used to draw the box. Choose File New to start a new drawing, and click the Start From Scratch button in the Create New Drawing dialog box. Here’s a summary of the steps to follow: