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There are actually two ways in which you can modify a block. One way is to completely redefine the block. Before AutoCAD 2000, this was the only way to make changes to a block. A second method for modifying blocks is to use the Reference Edit tool, which is new in AutoCAD 2000. The Reference Edit tool lets you quickly modify a block in its existing location. Reference Edit offers more flexibility when editing blocks and another type of object called an Xrcf, but it also has a few limitations. In this chapter, you’ll learn how to redefine a block by making changes to the door symbol. Later, in Chapter 6, you’ll see l.ow the Reference Edit tool a.iows you to quickly modify a block that will then affect other copies of the block throughout a drawing.

Saving a Block as a Drawing File

You’ve seen that, with very little effort, you can create a symbol that can be placed anywhere in a file. Suppose you want to use this symbol in other files. When you create a block using the Block command, the. block exists within the current file only until you specifically instruct Auto~AD to save it as a drawing file on disk. For an existing drawing that has been brought in and modified, such as the door, the drawing file  disk associated with that door is not automatically updated. To update the Door file, you must take an extra step and use the Export option on the File menu. Let’s see how this works.

Repladng Existing files with Blocks

The Wblock command does the same thing as File > Export, but output is limited to AutoCAD “.dwg files. (Veteran AutoCAD users should note that Wblock is now incorporated into the File> Export option.) Let’s try using the Wblock command this time to save the Door block you modified.
1. Issue the Wblock command by typing Wblock.J, or use the keyboard short. cut by typing w.J. The Write Block dialog box appears
2. In the Source button group, click the Block radio button.
3. Next, select Door from the drop-down list. Notice that the options under the  Destination button group change to reflect the location of the old Door. dwg file from which the Door block was originally inserted. You can keep the old name or enter a different name if you prefer.
4. In this case, you want to update the door you drew in Chapter 2, so click OK.
5. You’ll see a warning message telling you that the Door. dwg file alr v.dy exists . Go ahead and click Yes to confirm that you want to overwrite the old door drawing with the new door definition.
In this exercise, you typed the.Wblock command at the command prompt instead of using File >Export. The results are the same, regardless of which method you use. If you are in a hurry, the File >Export command is a quick way to save ‘part of your drawing as a file. The Wblock option may be easier for new users to use since it offers options in a dialog box .

Understanding the Write Block Dialog Box Options

The Write Block dialog box offers a way to save parts of your current drawing as a file. As you can see from the dialog box shown in step 1 of the previous exercise, you have several options to work with.

In the previous exercise, you used the Block option of the Source button group to select an existing block as the source object to be exported. You can also export a set of objects by choosing the Objects option. If you choose this option, the Base Point and Objects button groups become available. These options work the same way as their counterparts in the Block Definition dialog box that you saw earlier. when you created the Tub and Toilet blocks.
The third option in the Source button group, Entire Drawing, lets you export the whole drawing to its own file. This may seem to duplicate the File > Save As option in the menu bar, but saving the entire drawing from the Write Block dialog box actually performs some additional operations, such as stripping out unused blocks or other unused components. This has the effect of reducing file size. You’ll learn more about this feature later in this chapter.

Other Uses for Blocks

So far, you have used the Make Block tool to create symbols, and the Export and Wblock commands to save those symbols to disk. As you can see, symbols can be created and saved at any time while you are drawing. You have made the tub and toilet symbols into drawing files that you can see when you check the contents of your current directory. . However, creating symbols is not the only use for the Insert Block, Block, Export,
and Wblock commands. You can use them in any situation that requires grouping objects (though you may prefer to use the more flexible Object Group command discussed in the next section). You can also use blocks to stretch a set of objects along one axis. Export and Wblock also allow you to save a part of a drawin~ to disk. You will see instances of these other uses of the Block,Export, and Wblock commands throughout Chapters 5-8 and in Chapter 12. Make Block, Export, and Wblock are extremely versatile commands and, if used judiciously, can boost your productivity and simplify your work, If you are not careful, however, you can also get carried away and create more blocks than you can keep track of. Planning your drawings helps you determine which elements  ‘work best as blocks, and to recognize situations where other methods of organization will be more suitable.

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