Chapter 4
Organizing Objects with Blocks and Groups
Drawing the tub, toilet, and sink in Chapter 3, “Setting Up and Using AutoCAD’s Drafting Tools,” may have taken what seemed to you an inordinate amount of time. As you continue to use AutoCAD, however, you’ll learn to draw objects more quickly. You’ll also need to draw fewer of them because you can save drawings as symbols and then use those symbols like rubber stamps, duplicating drawings instantaneously wherever they’re needed. This saves a lot of time when you’re composing drawings.
To make effective use of AutoCAD, begin a symbol library of drawings you use frequently. A mechanical designer might have a library of symbols for fasteners, cams, valves, or other parts used in their application. An electrical engineer might have a symbol library of capacitors, resistors, switches, and the like. A circuit designer will have yet another unique set of frequently used symbols.
In Chapter 3, you drew three objects—a bathtub, a toilet, and a sink—that architects often use. In this chapter, you’ll see how to create symbols from those drawings.
In this chapter, you’ll learn to do the following:
- Create and insert a block
- Modify a block
- Understand the annotation scale
- Group objects
In word processors, the term block refers to a group of words or sentences selected for moving, saving, or deleting. You can copy a block of text elsewhere within the same file, to other files, or to a separate location on a server or USB storage device for future use. AutoCAD uses blocks in a similar fashion. In a file, you can turn parts of your drawing into blocks that can be saved and recalled at any time. You can also use existing drawing files as blocks.
You’ll start by opening the file you worked on in the previous chapter and selecting the objects that will become a block:
1. Start AutoCAD, and open the existing Bath file. Use the one you created in Chapter 3, or open the 04-bath.dwg sample file from this book’s companion website, www.sybex.com/go/masteringautocadmac. Metric users can use the 04-bath-metric.dwg file. The drawing appears just as you left it in the last session.
2. In the Tool Sets palette, click the Create icon, which starts the Block command. You can also choose Draw Block Make or type B↵, the keyboard alias for the Block command. This opens the Define Block dialog box (see Figure 4-1).
3. In the Name text box, type Toilet.
4. In the Base Point group, click the Pick Point button. This option enables you to select a base point for the block by using your cursor. (The insertion base point of a block is a point of reference on the block that is used like a grip.) When you’ve selected this option, the Define Block dialog box temporarily closes.
Notice that the Define Block dialog box gives you the option to specify the X, Y, and Z coordinates for the base point instead of selecting a point.
5. Using the Midpoint Osnap, pick the midpoint of the back of the toilet as the base point. Remember that you learned how to set up Running Osnaps in Chapter 3; all you need to do is point to the midpoint of a line to display the Midpoint Osnap marker and then left-click.
After you’ve selected a point, the Define Block dialog box reappears. Notice that the X, Y, and Z values in the Base Point group now display the coordinates of the point you picked. For two-dimensional drawings, the Z coordinate should remain at 0.
Next, you need to select the objects you want as part of the block.
6. Click the Select Objects icon in the Source Objects group. Once again, the dialog box momentarily closes. You now see the familiar Select objects: prompt in the Command Line palette, and the cursor becomes an Object Selection cursor. Click and drag from a point below and to the left of the toilet. Use the selection window to select the entire toilet. The toilet is now highlighted.
7. Press ↵ to confirm your selection. The Define Block dialog box opens again.
8. Select Inches from the Block Unit pop-up list. Metric users should select Centimeters.
Figure 4-1:The Define Block dialog box
9. Click the Description list box, and enter Standard Toilet.
10. Make sure the Retain Objects radio button in the Source Objects group is selected, and then click Create Block. The toilet drawing is now a block with the name Toilet.
11. Repeat the blocking process for the tub, but this time use the upper-left corner of the tub as the insertion base point and give the block the name Tub. Enter Standard Tub for the description.
You can press ↵ or right-click and choose Repeat BLOCK from the shortcut menu to start the Block command again.
When you turn an object into a block, it’s stored in the drawing file, ready to be recalled at any time. The block remains part of the drawing file even when you end the editing session. When you open the file again, the block is available for your use. In addition, you can access blocks from other drawings by using the AutoCAD Content palette, which you’ll learn about later in this chapter.
A block acts like a single object, even though it’s really made up of several objects. One unique characteristic of a block is that when you modify it, all instances of it are updated to reflect the modifications. For example, if you insert several copies of the toilet into a drawing and then later decide the toilet needs to be a different shape, you can edit the Toilet block and all the other copies of the toilet are updated automatically.
You can modify a block in a number of ways after it has been created. In this chapter, you’ll learn how to make simple changes to individual blocks by modifying the block’s properties. For more detailed changes, you’ll learn how to redefine a block after it has been created. Later in this chapter, you’ll learn how to use the Block Editor to make changes to blocks.
Make Sure You Select Objects When Creating Blocks
Make sure you use the Select Objects option in the Define Block dialog box to select the objects you want to turn into a block. AutoCAD lets you create a block that contains no objects, but if you try to proceed without selecting objects, you’ll get a warning message. This can cause confusion and frustration, even for an experienced user.
Understanding the Define Block Dialog Box
The Define Block dialog box offers several options that can help make using blocks easier. If you’re interested in these options, take a moment to review the Define Block dialog box as you read the descriptions. If you prefer, you can continue with the tutorial and come back to this section later.
You’ve already seen how the Name option lets you enter a name for your block. AutoCAD doesn’t let you complete the block creation until you enter a name.
You’ve also seen how to select a base point for your block. The base point is like the grip of the block: it’s the reference point you use when you insert the block back into the drawing. In the exercise, you used the Pick Point option to indicate a base point, but you also have the option to enter X, Y, and Z coordinates just below the Pick Point option. In most cases, however, you’ll want to use the Pick Point option to indicate a base point that is on or near the set of objects you’re converting to a block.
The Source Objects group of the Define Block dialog box lets you select the objects that make up the block. You use the Select Objects button to visually select the objects you want to include in the block you’re creating. Once you select a set of objects for your block, you’ll see a thumbnail preview of the block’s contents near the top center of the Define Block dialog box.
Other options in the Source Objects group and Block Behavior group let you specify what to do with the objects you’re selecting for your block. Table 4-1 shows a list of the options and what they mean.
Table 4-1: The Define Block dialog box options
| Option | Purpose |
| Source Objects group | |
| Select Objects | Lets you select the objects for the block after you click Create Block. |
| Convert To Block | Converts the objects you select into the block you’re defining. The block then acts like a single object after you’ve completed the Block command. |
| Retain Objects | Keeps the objects you select for your block as they are, unchanged. |
| Delete Objects | Deletes the objects you selected for your block. You may also notice that a warning message appears at the bottom of the Source Objects group. This warning appears if you haven’t selected objects for the block. After you’ve selected objects, the warning changes to tell you how many objects you’ve selected. |
| Base Point group | |
| Pick Point | Lets you select the base point for the block before you click Create Block to dismiss the dialog box. |
| X, Y, and Z input boxes | Enable you to enter exact coordinates for the block’s base point. |
| Block Behavior group | |
| Scale Uniformly | By default, blocks can have a different X, Y, or Z scale. This means they can be stretched in any of the axes. You can lock the X, Y, and Z scale of the block by selecting this option. That way, the block will always be scaled uniformly and can’t be stretched in one axis. |
| Allow Exploding | By default, blocks can be exploded or reduced to their component objects. You can lock a block so that it can’t be exploded by turning off this option. You can always turn on this option later through the Properties Inspector palette if you decide that you need to explode a block. |
| Annotative | Turns on the Annotative scale feature for blocks. This feature lets you use a single block for different scale views of a drawing. With this feature turned on, AutoCAD can be set to adjust the size of the block to the appropriate scale for the drawing. |
| Match Block Orientation To Layout | With the Annotative option turned on, this option is available. This option causes a block to appear always in its normal orientation regardless of the orientation of the layout view. |
| Block Unit | Lets you determine how the object is to be scaled when it’s inserted into the drawing using the Content palette. By default, this value is the same as the current drawing’s Insert value. |
| Description | Lets you include a brief description or keyword for the block. This option is helpful when you need to find a specific block in a set of drawings. |
| Open In Block Editor | If you turn on this option, the block is created and then opened in the Block Editor, described later in this chapter. |
You can recall the Tub and Toilet blocks at any time, as many times as you want. In this section, you’ll draw the interior walls of the bathroom first, and then you’ll insert the tub and toilet. Follow these steps to draw the walls:
1. Delete the original tub and toilet drawings. Click the Erase icon in the Tool Sets palette, and then enter All↵↵ to erase the entire visible contents of the drawing. (Doing so has no effect on the blocks you created previously.)
2. Draw a rectangle 7´-6˝ 5´. Metric users should draw a 228 cm 152 cm rectangle. Orient the rectangle so the long sides go from left to right and the lower-left corner is at coordinate 1´-10˝,1´-10˝ (or coordinate 56.0000,56.0000 for metric users).
If you use the Rectangle icon to draw the rectangle, make sure you explode it by using the Explode command (Modify Explode from the menu bar). This is important for later exercises. (See the section “Unblocking and Redefining a Block” later in this chapter if you aren’t familiar with the Explode command.) Your drawing should look like Figure 4-2.
Figure 4-2:The interior walls of the bathroom
Now you’re ready to place your blocks. Start by placing the tub in the drawing:
1. In the Tool Sets palette, click the Insert icon. You can also choose Insert Block from the menu bar or type I↵ to open the Insert Block dialog box (see Figure 4-3).
Figure 4-3:The Insert Block dialog box
2. Click the Blocks pop-up list to display a list of the available blocks in the current drawing.
3. Click the block name Tub.
4. Click Insert and you will see a preview image of the tub attached to the cursor. The upper-left corner you picked for the tub’s base point is now on the cursor intersection.
5. At the Specify insertion point or [Basepoint/Scale/X/Y/Z/Rotate]: prompt, pick the upper-left intersection of the room as your insertion point. The tub should look like the one in Figure 4-4.
Figure 4-4:The bathroom, first with the tub and then with the toilet inserted
You’ve got the tub in place. Now place the Toilet block in the drawing:
1. Open the Insert Block dialog box again, but this time select Toilet in the Blocks pop-up list.
2. Click the Insert button and then place the toilet at the location on the line along the top of the rectangle representing the bathroom wall, as shown in the bottom image in Figure 4-4.
Symbols for Projects Large and Small
A symbol library was a crucial part of the production of the San Francisco Main Library construction documents. Shown here is a portion of an AutoCAD floor plan of the library in which some typical symbols were used.
Notice the familiar symbols, such as the symbol for the door you created in Chapter 2, “Creating Your First Drawing.” And yes, there are even toilets in the lower half of the plan in the public restrooms. Symbol use isn’t restricted to building components. Room-number labels, diamond-shaped interior elevation reference symbols, and the hexagonal column grid symbols are all common to an architectural drawing, regardless of the project’s size. As you work through this chapter, keep in mind that all the symbols used in the library drawing were created using the tools presented here.
Scaling and Rotating Blocks
When you insert the tub, you have the option to scale or rotate the block before you place it in the drawing. After you have closed the Insert Block dialog box and before you click a location for the block, you can enter S↵ and enter a scale value or enter R↵ and enter a rotation angle. In addition, if you don’t like the point on the block that is used for the insertion, you can change it by entering B↵ and selecting a new insertion point.
You aren’t limited to scaling or rotating a block when it’s being inserted into a drawing. You can always use the Scale or Rotate icon or modify an inserted block’s properties to stretch it in one direction or another. This exercise shows you how this is done:
1. Click the Toilet block to select it.
2. In the Properties Inspector palette, click the All button. Take a moment to study the properties that appear. Toward the bottom, under the Geometry heading, you see a set of labels that show Position and Scale.
3. Let’s try making some changes to the toilet properties. Click the Scale X text box just to the right of the Scale X label.
4. Enter 1.5↵. Notice that the toilet changes in width as you do this.
5. You don’t really want to change the width of the toilet, so click in the Scale X text box and enter 1↵ to change the Scale X value back to 1. Press the Esc key to clear the selection.
If a block is created with the Scale Uniformly option turned on in the Define Block dialog box, you can’t scale the block in just one axis as shown in the previous exercise. You can only scale the block uniformly in all axes.
You’ve just seen how you can modify the properties of a block by using the Properties Inspector palette. In the exercise, you changed the X scale of the Toilet block, but you could have just as easily changed the Y value. You may have noticed other properties available in the Properties Inspector palette. You’ll learn more about those properties as you work through this chapter.
You’ve seen how you can turn a drawing into a symbol, known as a block in AutoCAD. Now you’ll see how you can use an existing drawing file as a symbol.
Using an Existing Drawing as a Symbol
You need a door into the bathroom. Because you’ve already drawn a door and saved it as a file, you can bring the door into this drawing file and use it as a block:
1. In the Tool Sets palette, click the Insert icon, or type I↵.
2. In the Insert Block dialog box, click the Browse button to open the Select Drawing File dialog box.
3. This is a standard file browser dialog box. Locate the Door file and double-click it. If you didn’t create a door file, you can use the door file from the Chapter 4 project files on this book’s companion website.
You can also browse your hard disk by looking at thumbnail views of the drawing files in a folder.
4. When you return to the Insert Block dialog box, click Insert. As you move the cursor around, notice that the door appears above and to the right of the cursor intersection, as in Figure 4-5.
5. At this point, the door looks too small for this bathroom. This is because you drew it 3 units long, which translates to 3˝. Metric users drew the door 9 cm long.
Figure 4-5:The door drawing being inserted in the Bath file
As mentioned earlier, you can specify a smaller or larger size for an inserted object. In this case, you want a 3´ door. Metric users want a 90 cm door. To get 3´ from a 3˝ door (or 90 cm from a 9 cm door), you need an X scale factor of 12, or 10 for metric users. (You may want to review “Understanding Scale Factors” in Chapter 3 to see how this is determined.)
6. At the Specify insertion point or [Basepoint/Scale/X/Y/Z/Rotate]: prompt, enter S↵ 12↵. Metric users should enter S↵ 10↵.
7. Pick a point between the bottom of the toilet and the lower wall of the bathroom so that the door is placed in the lower-right corner of the room.
You would expect to see the door, but nothing seems to happen to the drawing. This is because when you enlarged the door, you also enlarged the distance between the base point and the object. This brings up another issue to be aware of when you’re considering using drawings as symbols: All drawings have base points. The default base point is the absolute coordinate 0,0, otherwise known as the origin, which is located in the lower-left corner of any new drawing. When you drew the door in Chapter 2, you didn’t specify the base point. When you try to bring the door into this drawing, AutoCAD uses the origin of the door drawing as its base point (see Figure 4-6).
Figure 4-6:By default, a drawing’s origin is also its insertion point. You can change a drawing’s insertion point by using the Base command.
Because the door appears outside the bathroom, you must first choose View Zoom All from the menu bar to show more of the drawing and then use the Move icon in the Tool Sets palette to move the door to the right-side wall of the bathroom. Let’s do this now:
1. Choose View Zoom All from the menu bar to display the area set by the limits of your drawing plus any other objects that are outside those limits. You can also enter Z↵ A↵. The view of the room shrinks and the door is displayed. Notice that it’s now the proper size for your drawing (see Figure 4-7).
Figure 4-7:The enlarged door
2. Choose the Move icon from the Tool Sets palette, or type M↵.
3. To pick the door you just inserted, at the Select objects: prompt, click a point anywhere on the door and press ↵. Notice that now the entire door is highlighted. This is because a block is treated like a single object, even though it may be made up of several lines, arcs, and so on.
4. At the Specify base point or [Displacement] <Displacement>: prompt, turn on Running Osnaps, and pick the lower-left corner of the door. Remember that pressing Function-F3 or clicking Object Snap in the status bar toggles Running Osnaps on or off.
5. At the Specify second point or <use first point as displacement>: prompt, right-click and choose Snap Override Nearest and then position the door along the right wall so that your drawing looks like Figure 4-8.
Because the door is an object that you’ll use often, it should be a common size so you don’t have to specify an odd value every time you insert it. It would also be helpful if the door’s insertion base point were in a more convenient location; that is, a location that would let you place the door accurately within a wall opening. Next you’ll modify the Door block to better suit your needs.
Figure 4-8:The door on the right-side wall of the bathroom
You can modify a block in three ways. One way is to completely redefine it. In earlier releases of AutoCAD, this was the only way to make changes to a block. A second way is to use the Block Editor.
In the following sections, you’ll learn how to redefine a block by making changes to the door symbol. Later you’ll see how the Block Editor lets you easily edit a block.
To edit most objects, you can either use their grips or use the Properties Inspector palette. A few other objects will offer additional editing tools when you double-click on them. If you double-click a block, the Block Editor appears, which enables you to edit a block directly without having to redefine it. First you’ll learn how you can redefine a block.
Unblocking and Redefining a Block
One way to modify a block is to break it down into its components, edit them, and then turn them back into a block. This is called redefining a block. If you redefine a block that has been inserted in a drawing, each occurrence of that block in the current file changes to reflect the new block definition. You can use this block-redefinition feature to make rapid changes to a design.
To separate a block into its components, use the Explode command:
1. Click Explode in the Tool Sets palette. You can also choose Modify Explode from the menu bar or type X↵ to start the Explode command.
2. Click the door, and press ↵ to confirm your selection.
Insert and Explode at the Same Time
You can simultaneously insert and explode a block by clicking the Explode Block check box in the Insert Block dialog box.
Now you can edit the individual objects that make up the door, if you desire. In this case, you want to change only the door’s insertion point because you’ve already made it a more convenient size. You’ll turn the door back into a block, this time using the door’s lower-left corner for its insertion base point:
1. In the Tool Sets palette, click the Create icon. You can also choose Draw Block Make from the menu bar or type B↵.
2. In the Define Block dialog box, select Door from the Name pop-up list.
3. Click the Pick Point button, and pick the lower-left corner of the door.
4. Click the Select Objects button, and select the components of the door. Press ↵ when you’ve finished making your selection.
5. Select the Convert To Block option in the Source Objects group to automatically convert the selected objects in the drawing into a block.
6. Select Inches (or Centimeters for metric users) from the Block Unit pop-up list, and then enter Standard door in the Description box.
7. Click Create Block. You see a warning message that reads, The block definition has changed. Do you want to redefine it? You don’t want to redefine an existing block accidentally. In this case, you know you want to redefine the door, so click the Redefine button to proceed.
In step 7, you received a warning message that you were about to redefine the existing Door block. But originally you inserted the door as a file, not as a block. Whenever you insert a drawing file by using the Insert icon, the inserted drawing automatically becomes a block in the current drawing. When you redefine a block, however, you don’t affect the drawing file you imported. AutoCAD changes only the block in the current file.
You’ve just redefined the door block. Now place the door in the wall of the room:
1. Click the Erase icon in the Tool Sets palette, and then click the door. Notice that the entire door is one object instead of individual lines and an arc. Had you not selected the Convert To Block option in step 5 of the previous exercise, the components of the block would have remained individual objects.
2. Press ↵ to erase the door.
3. Insert the Door block again by using the Insert icon on the Tool Sets palette. This time, use the Nearest Snap override on the right-click shortcut menu, and pick a point on the right-side wall of the bathroom, near coordinate 9´-4˝,2´-1˝. Metric users should insert the door near 284,63.4.
4. Use the Grips feature to mirror the door, using the wall as the mirror axis so that the door is inside the room. To mirror an object using grips, select the objects to mirror, click a grip, and right-click. Select Mirror from the shortcut menu; then, indicate a mirror axis with the cursor. Press Esc to clear your selection.
Your drawing will look like Figure 4-9.
Figure 4-9:The bathroom floor plan thus far
Next you’ll see how you can update an external file with a redefined block.
Exploring the Block Editor
The Block Editor offers an easy way to make changes to existing blocks. It is especially useful if you just need to make a minor change to a block or if you want to create a new block that is a variation of an existing one. The Block Editor offers a safer way to edit blocks that are inserted at different scales in your drawing because you can’t accidentally resize the original size of the block components.
As an introduction to the Block Editor, you’ll make changes to the Toilet block. Open the 04b-bath.dwg file, and double-click the toilet in the plan to open the Block Editor. You see an enlarged view of the toilet in the drawing area with a light gray background (Figure 4-10). The gray background tells you that you’re in the Block Editor. You’ll also see the Block Editor options along the top of the drawing area.
Figure 4-10:The Block Editor with the Toilet block opened
The Block Editor lets you edit a block using all the standard AutoCAD editing tools. In the following exercise, you’ll modify the toilet and save your changes to the drawing:
1. Add the two lines shown in Figure 4-11.
Figure 4-11:The toilet with lines added
2. Click Save New from the Block Editor options. The Save Block Definition As dialog box appears (Figure 4-12).
Figure 4-12:The Save Block Definition As dialog box.
At this dialog box, you have the option to save the block as an external drawing file by checking the Save Block As Drawing check box. You can also replace an existing block by selecting the name of the block from the list to the left. Or you can enter an entirely different name in the text box at the top left to create a new block.
3. Click Toilet from the list to replace the existing block.
4. Click Save Block.
5. A message appears asking if you want to redefine the Toilet block. Click the Redefine block option.
6. Click Cancel from the Block Editor menu. Now the Toilet block appears with the added lines.
7. After reviewing the changes, close the 04b-bath.dwg file without saving it.
As you can see, editing blocks with the Block Editor is simple and straightforward. In this example, you added some lines to the Toilet block, but you can perform any type of drawing or editing to modify the block.
Saving a Block as a Drawing File
You’ve seen that, with little effort, you can create a symbol and place it anywhere in a file. Suppose you want to use this symbol in other files. When you create a block by using the Block command, the block exists in the current file only until you specifically instruct AutoCAD to save it as a drawing file on disk. When you have an existing drawing that has been brought in and modified, such as the door, the drawing file on disk associated with that door isn’t automatically updated. To update the Door file, you must take an extra step and choose File Export on the menu bar. Let’s see how this works.
Start by turning the Tub and Toilet blocks into individual files on disk:
1. Press the Esc key to make sure nothing is selected and no command is active.
2. From the menu bar, choose File Export to open the Export Data dialog box, which is a simple file dialog box.
3. Open the File Format pop-up list, and select Block (*.dwg).
4. Double-click the Save As text box and enter Tub.
5. Click the Save button to close the Export Data dialog box.
6. At the Enter name of existing block or [= (block=output file)/* (whole drawing)] <define new drawing>: prompt, enter the name of the block you want to save to disk as the tub file—in this case, Tub ↵.
The Tub block is now saved as a file.
7. Repeat steps 1 through 6 for the Toilet block. Give the file the same name as the block.
Replacing Existing Files with Blocks
The Wblock command does the same thing as choosing File Export, but output is limited to AutoCAD DWG files. Let’s try using the Wblock command this time to save the Door block you modified:
1. Issue the Wblock command by typing WBLOCK↵, or use the keyboard shortcut by typing w↵. This opens the Write Block dialog box (see Figure 4-13).
2. In the Save Location group, click the Block radio button.
Figure 4-13:The Write Block dialog box
3. Select Door from the pop-up list to the right of the Block radio button.
4. In this case, you want to update the door you drew in Chapter 2. Click the Browse button just below the Save Location pop-up list.
5. Locate and select the original Door.dwg file that you inserted earlier. Click Save.
6. A warning message appears: "Door.dwg" already exists. Do you want to replace it? Click Replace.
7. Click Write Block. A warning message tells you that the Door.dwg file already exists. Go ahead and click the “Replace the existing….” option 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 choosing File Export. The results are the same regardless of which method you use. If you’re in a hurry, the Wblock command is a quick way to save part of your drawing as a file. The File Export option might be easier for new users because it is a little easier to remember and follows the standard method for exporting files.
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 the previous exercise, you have several options.
In that exercise, you used the Block option of the Save Location group to select an existing block as the source object to be exported. You can also export a set of objects by choosing the Selected Objects option. If you choose this option, the Base Point and Source Objects groups become available. These options work the same way as their counterparts in the Define Block dialog box, which you saw earlier when you created the Tub and Toilet blocks.
The other option in the Save Location group, Entire Drawing, lets you export the whole drawing to its own file. This may seem to duplicate the Save As option in the File menu on the menu bar, but saving the entire drawing from the Write Block dialog box 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’ve used the Create icon to create symbols, and you’ve used the Export and Wblock commands to save those symbols to disk. As you can see, you can create symbols and save them at any time while you’re drawing. You’ve made the tub and toilet symbols into drawing files that you can see when you check the contents of your current folder.
However, creating symbols isn’t the only use for the Block, Export, and Wblock commands. You can use them in any situation that requires grouping objects. You can also use blocks to stretch a set of objects along one axis by using the Properties Inspector palette. Export and Wblock also enable you to save a part of a drawing to disk. You’ll see instances of these other uses of the Block, Export, and Wblock commands throughout the book.
Block, Export, and Wblock are extremely versatile commands, and if used judiciously, they can boost your productivity and simplify your work. If you aren’t careful, however, you can get carried away and create more blocks than you can track. Planning your drawings helps you determine which elements will work best as blocks and recognize situations in which other methods of organization are more suitable.
Another way of using symbols is to use AutoCAD’s external reference capabilities. External reference files, known as Xrefs, are files inserted into a drawing in a way similar to how blocks are inserted. The difference is that Xrefs don’t become part of the drawing’s database. Instead, they’re loaded along with the current file at startup time. It’s as if AutoCAD opens several drawings at once: the main file you specify when you start AutoCAD and the Xrefs associated with the main file.
By keeping the Xrefs independent from the current file, you make sure that any changes made to the Xrefs automatically appear in the current file. You don’t have to update each inserted copy of an Xref. For example, if you use the Insert DWG Reference option on the menu bar to insert the tub drawing and later you make changes to the tub, the next time you open the Bath file, you’ll see the new version of the tub.
Xrefs are especially useful in workgroup environments, where several people are working on the same project. One person might be updating several files that have been inserted into a variety of other files. Before Xrefs were available, everyone in the workgroup had to be notified of the changes and had to update all the affected blocks in all the drawings that contained them. With Xrefs, the updating is automatic. Many other features are unique to these files. They’re discussed in more detail in Chapters 7 and 14.
Understanding the Annotation Scale
One common use for AutoCAD’s block feature is creating reference symbols. These are symbols that refer the viewer to other drawings or views in a set of drawings. An example would be a building-section symbol on a floor plan that directs the viewer to look at a location on another sheet to see a cross-section view of a building. Such a symbol is typically a circle with two numbers: One is the drawing sheet number and the other is the view number on the sheet (examples appear a little later, in Figure 4-18).
In the past, AutoCAD users had to insert a reference symbol block multiple times to accommodate different scales of the same view. For example, the same floor plan might be used for a ¼˝ = 1´-0˝ scale view and a 1⁄8˝ = 1´-0˝ view. An elevation symbol block that works for the ¼˝ = 1´-0˝ scale view would be too small for the 1⁄8˝ = 1´-0˝ view, so two copies of the same block were inserted, one for each scale. The user then had to place the two blocks on different layers to control their visibility. In addition, if sheet numbers changed, the user had to make sure every copy of the elevation symbol block was updated to reflect the change.
The annotation scale feature does away with this need for redundancy. You can now use a single instance of a block even if it must be displayed in different scale views. To do this, you must take some additional steps when creating and inserting the block. Here’s how you do it:
1. Draw your symbol at the size it should appear when plotted. For example, if the symbol is supposed to be a ¼˝ circle on a printed sheet, draw the symbol as a ¼˝ circle.
2. Open the Define Block dialog box by choosing the Create icon from the Tool Sets palette.
3. Turn on the Annotative option in the Block Behavior section of the Define Block dialog box. You can also turn on the Match Block Orientation To Layout option if you want the symbol to appear always in a vertical orientation (see Figure 4-14).
Figure 4-14:The Define Block dialog box’s Block Behavior group with the Annotative option turned on
4. Select the objects that make up the block, and indicate an insertion point as usual.
5. Give the block a name, and then click Create Block.
After you’ve followed these steps, you need to apply an annotation scale to the newly created block:
1. Click the new block to select it.
2. Right-click and choose Annotative Object Scale Add/Delete Scales. The Annotation Object Scale List dialog box appears (see Figure 4-15).
Figure 4-15:The Annotation Object Scale List dialog box
3. Click the Add button, which looks like a plus sign at the bottom of the list box. The Add Scales To Object dialog box appears (see Figure 4-16).
Figure 4-16:The Add Scales To Object dialog box
4. Select from the list the scale you’ll be using with this block. You can F-click to select multiple scales. When you’re finished selecting scales, click OK. The selected scales appear in the Annotation Object Scale List dialog box.
5. Click OK to close the Annotation Object Scale List dialog box.
At this point, the block is ready to be used in multiple scale views. You need only to select a scale from the Model view’s Annotation Scale pop-up list or the layout view’s Viewport Scale pop-up list (see Figure 4-17), which are both in the lower-right corner of the status bar.
Figure 4-17:The Model Space Annotation Scale (left) and layout view’s Viewport Scale (right) pop-up lists
The Annotation Scale pop-up list appears in model view, and the Viewport Scale pop-up list appears in layout view and when a viewport is selected. (See Chapter 15, “Laying Out Your Printer Output,” for more about layouts and viewports.) In layout view, you can set the Viewport Scale value for each individual viewport so the same block can appear at the appropriate size for different scale viewports (see Figure 4-18).
Figure 4-18:A single block is used to create building section symbols of different sizes in these layout views. Both views show the same floor plan displayed at different scales.
Note that if you want to use several copies of a block that is using multiple annotation scales, you should insert the block and assign the additional annotation scales, and then make copies of the block. If you insert a new instance of the block, the block acquires only the annotation scale that is current for the drawing. You’ll have to assign additional annotation scales to each new insertion of the block.
If you’re uncertain whether an annotation scale has been assigned to a block, you can click the block and you’ll see the different scale versions of the block as ghosted images. Also, if you hover over a block, triangular symbols appear next to the cursor for blocks that have been assigned annotative scales.
If you need to change the position of a block for a particular layout viewport scale, go to Model view, select the appropriate scale from the Annotation Scale pop-up list, and then adjust the position of the block.
Blocks are extremely useful tools, but for some situations, they’re too restrictive. At times, you’ll want to group objects so they’re connected but can still be edited individually.
For example, consider a space planner who has to place workstations on a floor plan. Although each workstation is basically the same, some slight variations in each station could make the use of blocks unwieldy. For instance, one workstation might need a different configuration to accommodate special equipment, and another workstation might need to be slightly larger than the standard size. You would need to create a block for one workstation and then, for each variation, explode the block, edit it, and create a new block. A better way is to draw a prototype workstation and turn it into a group. You can copy the group into position and then edit it for each individual situation without losing its identity as a group.
The following exercise demonstrates how grouping works:
1. Save the Bath file, and then open the drawing Office1.dwg from the sample files from this book’s companion website. Metric users should open Office1-metric.dwg.
2. Use the Zoom command to enlarge just the view of the workstation, as shown in the first image in Figure 4-19.
Figure 4-19:A workstation in an office plan
3. Type G↵ or Group↵.
4. Type C↵ to use the Create option.
5. Type Station1↵ for the group name and then press ↵ at the Description prompt.
6. At the Select objects: prompt, use a window to select the entire workstation in the lower-left corner of the plan, and press ↵. You’ve just created a group.
Now whenever you want to select the workstation, you can click any part of it to select the entire group. At the same time, you can still modify individual parts of the group—the desk, partition, and so on—without losing the grouping of objects (see the following section).
Modifying Members of a Group
Next you’ll make copies of the original group and modify the copies. Figure 4-20 is a sketch of the proposed layout that uses the new workstations. Look carefully and you’ll see that some of the workstations in the sketch are missing a few of the standard components that exist in the Station1 group. One pair of stations has a partition removed; another station has one fewer chair.
Figure 4-20:A sketch of the new office layout
The exercises in this section show you how to complete your drawing to reflect the design requirements of the sketch.
Start by making a copy of the workstation:
1. Click the Copy icon on the Tool Sets palette, or type CO↵, and click the Station1 group you just created. Notice that you can click any part of the station to select the entire station. If only a single object is selected, press 
-
-A and try clicking another part of the group.
2. Press ↵ to finish your selection.
3. At the Specify base point or [Displacement/mOde] <Displacement>: prompt, enter @↵. Then enter @8´2˝<90 to copy the workstation 8´-2˝ vertically. Metric users should enter @249<90. Press ↵ to exit the Copy command.
You can also use the Direct Distance method by typing @↵ and then pointing the rubber-banding line 90° and typing 8´2˝↵. Metric users should type 249↵.
4. Issue the Copy command again, but this time click the copy of the workstation you just created. Notice that it, too, is a group.
5. Copy this workstation 8´-2˝ (249 cm for the metric users) vertically, just as you did the original workstation. Press ↵ to exit the Copy command.
Next you’ll use grips to mirror the first workstation copy:
1. Click the middle workstation to highlight it, and notice that grips appear for all the entities in the group.
2. Click the grip in the middle-left side, as shown in Figure 4-21.
Figure 4-21:Mirroring the new group by using grips
3. Right-click, and choose Mirror from the shortcut menu. Notice that a temporary mirror image of the workstation follows the movement of your cursor.
4. Turn on Ortho mode, and pick a point directly to the right of the hot grip you picked in step 2. The workstation is mirrored to a new orientation.
5. Press the Esc key to clear the grip selection. Also, turn off Ortho mode.
Now that you’ve got the workstations laid out, you need to remove some of the partitions between the new workstations. If you had used blocks for the workstations, you would first need to explode the workstations that have partitions you want to edit. Groups, however, let you make changes without undoing their grouping.
Use these steps to remove the partitions:
1. At the Command prompt, press --A. You should see the <Group off> message in the command line. If you see the <Group on> message instead, press --A until you see <Group off>. This turns off groupings so you can select and edit individual objects within a group.
2. Erase the partition that divides the two copies of the workstations, as shown in Figure 4-22. Since you made a mirror copy of the original workstation, you’ll need to erase two partitions, the original and the copy.
Figure 4-22:Remove the partitions between the two workstations.
3. Press --A again to turn groupings back on.
4. To check your workstations, click one of them to see whether all its components are highlighted together.
5. Close the file when you’re finished. You don’t need to save your changes.
Working with the Group Options
Each group has a unique name, and you can also attach a brief description of a group while you are creating it. When you copy a group, AutoCAD assigns an arbitrary name to the newly created group. Copies of groups are considered unnamed.
Objects in a group aren’t bound solely to that group. One object can be a member of several groups, and you can have nested groups (groups with groups).
Figure 4-23 shows the Group options in the Command Line palette and Table 4-2 gives a rundown of the options available in the Group command.
Figure 4-23:The Group options in the Command Line palette
Table 4-2: Group options
| Option | Purpose |
| Add | Use this option to add objects to a group. While you’re using this option, grouping is temporarily turned off to allow you to select objects from other groups. |
| Create | This option creates a group. You are prompted for a name and description. |
| Explode | Use this option to separate a group into its individual components. |
| Order | Use this option to change the order of objects in a group. The order refers to the order in which you selected the objects to include in the group. You can change this selection order for special purposes such as tool-path machining. |
| Remove | This option removes objects from a group. |
| Rename | Use this option to rename a group. |
| Selectable | Use this option to turn individual groups on and off. When a group is selectable, it can be selected only as a group. When a group isn’t selectable, the individual objects in a group can be selected, but not the group. |
If a group is selected, you can remove individual items from the selection with a shift-click. In this way, you can isolate objects within a group for editing or removal without having to turn off groups temporarily.
You’ve seen how you can use groups to create an office layout. You can also use groups to help you keep sets of objects temporarily together in a complex drawing. Groups can be especially useful in 3D modeling when you want to organize complex assemblies together for easy selection.
Create and insert a block. If you have a symbol that you use often in a drawing, you can draw it once and then turn it into an AutoCAD block. A block can be placed in a drawing multiple times in any location, like a rubber stamp. A block is stored in a drawing as a block definition, which can be called up at any time.
Master It Name the dialog box used to create a block from objects in a drawing, and also name the tool to open this dialog box.
Modify a block. Once you’ve created a block, it isn’t set in stone. One of the features of a block is that you can change the block definition and all the copies of the block are updated to the new definition.
Master It What is the name of the tool used to “unblock” a block?
Understand the annotation scale. In some cases, you’ll want to create a block that is dependent on the drawing scale. You can create a block that adjusts itself to the scale of your drawing through the annotation scale. When the annotation scale feature is turned on for a block, the block can be set to appear at the correct size depending on the scale of your drawing.
Master It What setting in the Define Block dialog box turns on the annotation scale feature, and how do you set the annotation scale of a block?
Group objects. Blocks can be used as a tool to group objects together, but blocks can be too rigid for some grouping applications. AutoCAD offers groups, which are collections of objects that are similar to blocks but aren’t as rigidly defined.
Master It How are groups different from blocks?