194 Part II Drawing in Two Dimensions

Summary

All drawings need to be edited, either as part of the drawing process or to make corrections. In this chapter, you read about:

Erasing objects

Moving objects

Copying objects

Rotating objects

Scaling objects

Using the CHANGE command on lines and circles

The many ways of selecting objects

Customizing the object-selection features

The next chapter covers the more-advanced editing commands and options.

196 Part II Drawing in Two Dimensions

The command then asks if you want to erase the source objects. The source objects are the objects you have selected to mirror. If you want to keep them, type n or press Enter. You keep the source objects when you’re building a symmetrical model and want the mirror image to be added to the original object(s). Type y when you want to edit an object (change its orientation) so that only the mirror image is retained in the drawing.

STEPS: Mirroring Objects

1.Open ab07-02.dwg from the Results folder of the CD-ROM. If you completed the exercise on arcs in Chapter 7, you can open this drawing from your AutoCAD Bible folder.

2.Save the file as ab10-01.dwg in your AutoCAD Bible folder. Make sure OSNAP is on. Set a running object snap for intersections only.

3.Choose Erase on the Modify toolbar. At the Select objects: prompt, pick the line and two arcs to the bottom-right of the two centerlines and then press Enter. The resulting model should look like Figure 10-1.

4.Choose Mirror from the Modify toolbar. At the Select objects: prompt, pick the remaining exterior line and two arcs, and press Enter.

5.At the Specify first point of mirror line: prompt, pick intersection 1in Figure 10-1. At the Specify second point of mirror line: prompt, pick intersection 2.

6.The command prompts: Erase source objects? [Yes/No] <N>: Press Enter to accept the default, No.

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Figure 10-1: A partially completed mounting plate.

7.Again choose Mirror from the Modify toolbar. At the Select objects: prompt, type p to pick the original lines. Then pick the new exterior line and two arcs, and then press Enter.

8.At the Specify first point of mirror line: prompt, pick intersection 2. At the Specify second point of mirror line: prompt, pick intersection 3. Press Enter again at the Erase source objects? [Yes/No] <N>: prompt.

9.The command completes the mounting plate. Save your drawing. It should look like Figure 10-2.

Figure 10-2: The completed mounting plate.

Using the ARRAY command

The ARRAY command creates a rectangular or polar (circular) pattern by copying the object(s) you select as many times as you specify. The ARRAY command is a powerful drawing tool. It can quickly create large numbers of objects, thus saving a huge amount of time and effort.

Rectangular arrays

A rectangular array creates a grid of rows and columns of one or more objects. Figure 10-3 shows an example of a rectangular array. To create a rectangular array, follow these steps:

Figure 10-3: The garage door was drawn with one panel, as shown on the left side. A rectangular array created the rest of the door panels, as shown on the right.

Thanks to Henry Dearborn, AIA, Fairfield, Iowa, for this drawing.

1.Select the object or objects and choose Array from the Modify toolbar. Alternatively,

choose Array from the Modify toolbar and select the object or objects. The Array dialog box opens, as shown in Figure 10-4.

198 Part II Drawing in Two Dimensions

Figure 10-4: The Array dialog box.

2.Click Rectangular Array at the upper-left corner of the dialog box (if it is not already selected).

3.If you’ve already selected one or more objects, the dialog box indicates the number of selected objects. If you haven’t selected any object, click Select Objects to return to your drawing and select objects. Press Enter to end object selection and return to the dialog box.

4.In the Rows and Columns text boxes, type the total number of rows and columns that you want.

5.Type the distance you want between the rows in the Row Offset text box. The preview panel doesn’t display any change when you change the row or column offsets.

6.Type the distance you want between the columns in the Column Offset text box.

7.If you want to specify the offsets by picking points on your screen, click one of the following buttons:

•Pick Both Offsets

• Pick Row Offset

• Pick Column Offset

8.If you want to change the angle of the array, type an angle in the Angle of Array

text box. The preview panel displays the results of this value. To specify the angle by picking, click the Pick Angle of Array button.

9.To preview the array, click Preview. Then choose Accept to create the array, Modify to return to the Array dialog box, or Cancel to end the command.

10.To create the array, click OK.

If you change the Snap angle or the UCS (as explained in Chapter 8), AutoCAD and AutoCAD LT create the rectangular array at the angle of the snap or UCS.

Polar (circular) arrays

A polar array creates copies of one or more objects arrayed in a circle around a center point. An example of a polar array is shown in Figure 10-5.

Figure 10-5: The pulley was drawn with one spoke, as shown on the left.

A polar array created the additional spokes.

Thanks to Robert Mack of the Dexter Company, Fairfield, Iowa, for this drawing.

To create a polar array, follow these steps:

1.Select the object or objects and choose Array from the Modify toolbar. Alternatively, choose Array from the Modify toolbar and select the object or

objects. The Array dialog box opens.

2.Click Polar Array at the top of the dialog box (if it is not already selected).

3.If you’ve already selected one or more objects, the dialog box indicates the number of selected objects. If you haven’t selected any objects, click Select objects to return to your drawing and select objects. Press Enter to end object selection and return to the dialog box.

4.Specify the center point by typing X and Y coordinates, or click the Pick Center Point button. If you selected an object first, check that the center point displayed

is what you want.

5.Select the two items that you want to specify from the Method drop-down box. You can choose any two from the three choices:

•Total Number of Items: Sets the total number of items in the resulting array, including the one that you are arraying.

•Angle to Fill: Sets the number of degrees that the polar array covers. For example, to array around half of a circle, specify 180°.

•Angle Between Items: Specifies the number of degrees between each item in the polar array.

200 Part II Drawing in Two Dimensions

6.Complete the values of the two items that you specified. You can click the buttons to pick the angle to fill or the angle between items on the screen.

7.Check the Rotate Items as Copied check box to rotate the objects that you are arraying. Uncheck the box to leave them unrotated.

8.Click Preview to preview the array. Then choose Accept to create the array, Modify to return to the dialog box, or Cancel to cancel the command.

9.Click OK to create the array.

You can specify which point on the last object selected that AutoCAD and AutoCAD LT uses to array the objects. The command makes a calculation of the distance from the center point of the array to a base point on the last object selected. Otherwise, the command uses a default point based on the type of object selected. Table 10-1 lists the default base points. If you are arraying more than one object, you may not obtain the result you want without specifying the base point. Even for one object, you may want to change the base point that is used.

To specify the base point, click the More button at the bottom of the dialog box. The dialog box opens up to display the Object Base Point section. Uncheck Set to Object’s Default. You can then either type in coordinates or, more likely, click the Pick Base Point button and use an object snap to pick the desired point on an object. The preview box adjusts according to your choice but, because the preview only shows rectangles in the place of your object, the display may not be very helpful.

You can use the Express Tools COPYM command to enhance your copying options. Choose Express Modify Multiple Copy. You can create evenly spaced copies between two points, copy objects according to a specified measurement, and create arrays. For information on installing the Express Tools, see Appendix A.

Table 10-1: Object Base Points for Arrays

STEPS: Arraying Objects

1.Open ab10-a.dwg from the CD-ROM.

2.Save the file as ab10-02.dwg in your AutoCAD Bible folder. It looks like Figure 10-6. OSNAP should be on. Set center and intersection running object snaps.

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Figure 10-6: A partially completed mounting bracket.

3. Choose Array on the Modify toolbar. The Array dialog box opens.

4.Click the Select Objects button of the Array dialog box. In the drawing, pick the horizontal centerline 1 in Figure 10-6 and then press Enter. You return to the dialog box.

5.Make sure that Rectangular Array is selected at the top of the dialog box.

6.In the Rows text box, type 4. In the Columns text box, type 1.

7.In the Row Offset text box, type 1. (You don’t need to specify the column offset because you are creating only one column.)

8.Click Preview. You should see a total of four horizontal lines, as shown in Figure 10-7. Click Accept in the small dialog box that appears. (If you don’t see the four lines, click Modify and recheck the settings in the Array dialog box.)

9.To add the holes to the pattern, again choose Array from the Modify toolbar.

10.Click the Select Objects button in the Array dialog box. In the drawing, pick circle 2 in Figure 10-6 and then press Enter.

11.Back in the Array dialog box, type 4 in the Rows text box and type 2 in the Columns text box.

12.Click the Pick Both Offsets button. In the drawing, pick the center of circle 2 and the intersection of centerlines near 3 in Figure 10-6. (You can also pick the intersection of centerlines at the center of circle 2. If necessary, press Tab until you see the object snap that you want.)

202 Part II Drawing in Two Dimensions

13.Click Preview to preview the array. If the circles look like Figure 10-7, click Accept. Otherwise, click Modify and check your settings. After you’re done, the command arrays the holes to fit the centerlines.

14.To create a six-hole bolt circle, pick hole 4 in Figure 10-6.

15.Choose Array from the Modify toolbar.

16.In the Array dialog box, choose Polar Array.

17.Next to the Center Point text boxes, click the Pick Center Point button. In the drawing, pick the center of the large circle at 5 in Figure 10-6.

18.The Method should read “Total number of items and Angle to fill.” In the Total Number of Items text box, type 6. In the Angle to Fill text box, type 360.

19.Click Preview to see the array. It should look like Figure 10-7. If it does, click Accept. Otherwise, click Modify and recheck the settings in the Array dialog box. AutoCAD or AutoCAD LT completes the mounting bracket.

20.Save your drawing. It should look like Figure 10-7.

Figure 10-7: The completed mounting bracket.

Offsetting objects

The OFFSET command creates lines or curves parallel to one existing object. The beauty of this command is apparent when you start to create complex objects, such as polylines, which are covered in Chapter 16. Polygons and rectangles are polylines, which means that they’re treated as one object. For example, using OFFSET, you can create concentric polygons in one step. Figure 10-8 shows two concentric polygons. The outside polygon was created with the POLYGON command, and the inside polygon was created by using OFFSET.

To offset an object, choose Offset from the Modify toolbar. You cannot select objects before choosing the command.

The command responds with the following list of settings and prompt:

Current settings: Erase source=No Layer=Source OFFSETGAPTYPE=0 Specify offset distance or [Through/Erase/Layer] <Through>:

204 Part II Drawing in Two Dimensions

STEPS: Using the OFFSET Command

1.Open ab10-b.dwg from the CD-ROM.

2.Save the file as ab10-03.dwg in your AutoCAD Bible folder. It looks like Figure 10-9. Set a running object snap for center, and turn on OSNAP.

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Figure 10-9: A tension arm for a commercial dryer.

3.Choose Offset on the Modify toolbar. Follow the prompts:

Specify offset distance or [Through/Erase/Layer] <Through>: or specify the Through option if does not appear as the default.

Select object to offset or [Exit/Undo] <Exit>:

Pick 1 in Figure 10-9.

Specify through point or [Exit/Multiple/Undo] <Exit>: Pick the center

of 2.

Select object to offset or [Exit/Undo] <Exit>:

This action copies the centerline through the upper circles.

4.Choose Offset from the Modify toolbar again. At the Specify offset distance or [Through/Erase/Layer] <Through>: prompt, type 4-19/64 . Pick the centerline 3 at the Select object to offset or [Exit/Undo] <Exit>: prompt, and then click near 4 at the Specify point on side to offset or [Exit/Multiple/Undo] <Exit>: prompt. Press Enter to end the command. The vertical centerline appears 4-19/64 units to the right of the original.

5.Save your drawing. It should look like Figure 10-10.

Figure 10-10: The completed tension arm.

Aligning objects

The ALIGN command lets you move and rotate an object or objects in one procedure. It is especially useful in 3D work. By specifying where selected points on an object move, you can align the object with other objects in your drawing, as shown in Figure 10-11. See Chapter 24 for the use of the ALIGN command in 3D editing.

AutoCAD LT doesn’t include the ALIGN command. Instead, you would need to use a combination of the MOVE and ROTATE commands. The Reference option of the ROTATE command would be helpful to align objects. I discuss the MOVE and ROTATE commands in Chapter 9.

1st source point

1st destination point

2nd destination point 2nd source point

Figure 10-11: Aligning a door with a wall.

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Aligning requires several steps. Even so, it can save time when you need to move and rotate at the same time, especially if you don’t know the rotation angle that you need. To align an object, choose Modify 3D Operation Align and select an object or objects. Alternatively, select the object or objects first and then choose Modify 3D Operation Align. Then follow these steps:

STEPS: Aligning Objects in Two Dimensions

1.Open ab10-c.dwg from the CD-ROM.

2.Save the file as ab10-04.dwg in your AutoCAD Bible folder. It looks like Figure 10-12.

3.Choose Modify 3D Operation Align and follow the prompts:

Select objects: Select the horizontal angle by using a window, picking near 1 and then 2. Press Enter to end object selection. This angle needs to be aligned with the long, diagonal support angle. Specify first source point: Pick the endpoint at 3 in Figure 10-12.

Specify first destination point: Pick the endpoint at 4. Specify second source point: Pick the endpoint at 5.

Specify second destination point: Pick the endpoint at 6. Specify third source point or <continue>:

Scale objects based on alignment points? [Yes/No] <N>:

This action aligns the horizontal angle with the support angle.

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Figure 10-12: A base assembly for a commercial washing machine.

Thanks to Robert Mack of the Dexter Company, Fairfield, Iowa, for this drawing.

4. Save your drawing. It should look like Figure 10-13.

Figure 10-13: The washing machine base.