Many parts that include elliptical shapes do not use the entire ellipse. To draw these shapes, you can use the ELLIPSE Arc option.
1. Pick the down-facing arrow to the right of the Ellipse Axis, End button and select the Elliptical Arc button.
2. Pick three points similar to those shown in Fig. 5-8.
A temporary ellipse forms.
3. In reply to Specify start angle, pick a point anywhere on the ellipse.
4. As you slowly move the crosshairs counterclockwise, notice that an elliptical arc forms.
5. Pick a point to form an elliptical arc.
Donuts
TheDONUT command allows you to create thick-walled or solid circles, known in AutoCAD as donuts. Drafters commonly use donuts to represent features on a machine part, architectural drawing, or map.
1. Click inside the Draw panel title bar on the Ribbon to display the expanded panel, then select the Donut button.
2. Specify an inside diameter of .4 … 3. … and an outside diameter of .75.
The outline of a small donut locks onto the crosshairs and is ready to be dragged and positioned by its center.
4. Place the donut anywhere in the drawing by picking a point.
As noted in the previous chapter, temporary dotted lines appear when you move the crosshairs over existing objects on the screen. This feature allows you to align and create new points from the existing objects. Take advantage of the dotted horizontal line that appears when creating axis endpoint 2.
DRAW
DRAW
5. Move the crosshairs away from the new solid-fi lled donut and notice the Command line at the bottom of the screen.
6. Place several additional donuts in the drawing.
7. Press ENTER to terminate the command.
Rectangles
One of the most basic shapes used by drafters and designers is the rectangle.
You can create rectangles using the LINE command, but doing so has some disadvantages. For example, you would have to take the time to make sure that the corner angles are exactly 90°. Also, each line segment would be a separate object. Therefore, AutoCAD provides the RECTANG command, which allows you to create a rectangle with perfect corners and as a single object. Clicking anywhere on a rectangle created with the RECTANG command selects the entire rectangle.
1. On the Draw panel of the Ribbon, pick the Rectangle button.
As you can see, AutoCAD is asking for the fi rst corner of the rectangle. Other options appear in brackets at the Command line.
2. In reply to Specify fi rst corner point, pick a point at any location.
3. Move the pointing device in any direction and notice that a rectangle begins to form.
4. Pick a second point at any location to create the rectangle.
5. Create a second rectangle. Since the RECTANG command was just entered, reenter it by pressing the spacebar or ENTER, or right-click and pickRepeat RECTANG from the shortcut menu.
6. Create a third rectangle.
7. Close the drawing without saving it.
Polygons
ThePOLYGON command enables you to create regular polygons with 3 to 1024 sides. A regular polygon is one with sides of equal length. Using the POLYGON command, let’s insert the bolt head into the engine drawing you started earlier in this chapter.
DRAW
1. Open the engine.dwg fi le by picking the Open button from the abbreviated Quick Access toolbar.
2. On the expanded Draw panel of the Ribbon, pick the Polygon button, or enter the POL alias.
Notice the <4> at the end of the AutoCAD prompt. This is the default value, meaning that if you were to press ENTER now, AutoCAD would enter 4 in reply to Enter number of sides. To represent the bolt head shown in Fig. 5-2 on page 49, you will need a hexagon (six-sided polygon).
3. Enter 6.
AutoCAD now needs to know if you want to defi ne an edge of the polygon or select a center point. Let’s specify a center.
4. Move the pointing device over any of the larger circles in the drawing.
When the small yellow symbol appears at the center of the cylinder head, pick a point to select the center of the circle as the center point of the hexagon. (The Object Snap button on the status bar must be depressed.) AutoCAD allows you to create a polygon by inscribing it inside a circle of a specifi ed diameter or by circumscribing it around the specifi ed circle.
Figure 5-9 shows the difference.
5. Press ENTER to select the I (Inscribed) default value.
AutoCAD now wants to know the radius of the circle within which the polygon will appear.
6. With the pointing device, move the crosshairs from the center of the polygon and notice that a hexagon begins to form.
7. Pick a point to create the hexagonal bolt head at an appropriate size relative to the cylinder head. Refer to Fig. 5-2, if necessary.
DRAW
F i g . 5 - 9
To create the polygon with a more accurate size, you could have entered a specifi c numeric value, such as .5, at the key-board. (Entering a 0 before the decimal point is optional.)
The drawing of the cylinder head component is now complete. Your drawing should look similar to the one in Fig. 5-10. Note that the relative diameters of the circles and the size of the bolt head relative to the circles may be dif-ferent on your drawing because we did not use exact sizes in this drawing.
8. Save your work and exit AutoCAD.
QUICK ACCESS
Back up your fi les regularly. The few seconds required to make a backup copy may save you hours of work. Experienced users back up faithfully because they know the consequences of not doing so.
F i g . 5 - 1 0
Continued
• REVIEW QUESTIONS
Answer the following questions on a separate sheet of paper.
1. Briefl y describe the following methods of producing circles.
a. 2 points b. 3 points c. tan tan radius
2. In which Ribbon control panel are the Arc and Circle buttons found?
3. What function does the Arc Continue option serve?
4. Explain the purpose of the DONUT command.
5. When you create a polygon using the Inscribed in circle option, does the polygon appear inside or outside the imaginary circle?
6. What are the practical differences between creating a rectangle using the LINE command and creating it using the RECTANG command? Why might you choose one command instead of the other?
7. In addition to the LINE and RECTANG commands, which other command is capable of creating a rectangle? When might you choose this method?
• CHALLENGE YOUR THINKING
These questions are designed to further your knowledge of AutoCAD by encouraging you to explore the concepts presented in this chapter. Answer each question on a separate sheet of paper.
1. Review the information in this chapter about specifying an angle in degrees. How might you be able to create an arc in a clockwise direction?
Try your method to see if it works, and then write a paragraph describing the method you used.
2. Experiment further with the ARC command. Is it possible to create a single arc that has a noncircular curve using the options available for this command? (A noncircular curve is one in which not all the points are exactly the same distance from a common center point.) Explain your answer.