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# Isometric Drawing with AutoCAD 2020

This chapter is from the book

## Drawing Ellipses in Orthographic Views

The ELLIPSE command is important not only for drawing isocircles but also for drawing true ellipses in orthographic views. There is also an option to create elliptical arcs.

• orthographic view: One of six standard views in which the observer’s point of view is normal to the front, back, left, right, top, or bottom plane of the drawing.

An ellipse is determined by a center point and two perpendicular axes of differing lengths. In AutoCAD, these specifications can be shown in two nearly identical ways, each requiring you to show three points (see Figure 11-16). In the default method, you show two endpoints of an axis and then show half the length of the other axis, from the midpoint of the first axis out. (The midpoint of an axis is also the center of the ellipse.) The other method allows you to pick the center point of the ellipse first, then the endpoint of one axis, followed by half the length of the other axis.

• In preparation for this exercise, return to the standard Snap mode and Grid mode by clicking the ISODRAFT button on the status bar to turn off the isometric snap mode.

• Your grid is returned to the standard pattern of lines, and the crosshairs are horizontal and vertical again. Notice that this does not affect the isometric bracket you have just drawn.

We briefly explore the ELLIPSE command and draw some standard ellipses.

• Ortho should be off for this exercise.

• Pick the Axis, End tool from the Ellipse drop-down list on the Draw panel, as shown in Figure 11-17.

`Specify axis endpoint of ellipse or [Arc Center]:`
• Pick an axis endpoint, as shown by P1 on the ellipse at the lower left in Figure 11-18.

• AutoCAD prompts for the other endpoint:

`Specify other endpoint of axis:`
• Pick a second endpoint, as shown by P2.

• AutoCAD gives you an ellipse to drag and a rubber band so that you can show the length of the other axis. Only the length of the rubber band is significant; the angle is already determined to be perpendicular to the first axis. Because of this, the third point falls on the ellipse only if the rubber band happens to be exactly perpendicular to the first axis.

The prompt that follows allows you to show the second axis distance as before, or a rotation around the first axis:

`Specify distance to other axis or [Rotation]:`

The Rotation option is awkward to use, and we do not explore it here; see the AutoCAD Command Reference for more information.

• Pick P3 as shown.

• This point shows half the length of the other axis.

The first ellipse should now be complete. Now, we draw one showing the center point first, using the Center ellipse tool from the ribbon.

• Pick the Center tool from the Ellipse drop-down list on the Draw panel of the ribbon.

• This automates the entry of the Center option.

AutoCAD gives you a prompt for a center point:

`Specify center of ellipse:`
• Pick a center point, as shown by P1 at the middle left in Figure 11-18.

• Now, you have a rubber band stretching from the center to the end of an axis and the following prompt:

`Specify endpoint of axis:`
• Pick an endpoint, as shown by P2 in Figure 11-18.

• The prompt that follows allows you to show the second axis distance as before, or a rotation around the first axis:

`Specify distance to other axis or [Rotation]:`
• Pick an axis distance, as shown by P3.

• Here again the rubber band is significant for distance only. The point you pick falls on the ellipse only if the rubber band is stretched perpendicular to the first axis. Notice that it is not so in Figure 11-18.

### Drawing Elliptical Arcs

Elliptical arcs can be drawn by trimming complete ellipses or by using the Arc option of the ELLIPSE command. Using the Arc option, you first construct an ellipse in one of the two methods shown previously and then show the arc of the ellipse that you want to keep.

• Pick the Elliptical Arc tool from the Ellipse drop-down list on the Draw panel of the ribbon.

• Pick a first axis endpoint, as shown by P1 at the upper left in Figure 11-18.

• Pick a second endpoint, P2 in the figure.

• Pick P3 to show the second axis distance.

• AutoCAD draws an ellipse as you have specified, but the image is only temporary. Now, you need to show the arc you want drawn. The two options are Parameter and Included angle. Parameter takes you into more options that allow you to specify your arc in different ways, similar to the options of the ARC command. We’ll stick with the default option.

• Pick P4 to show the angle at which the elliptical arc begins.

• Move the cursor slowly now and you can see all the arcs that are possible starting from this angle.

• Pick P5 to indicate the end angle and complete the command.

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