AutoCAD 2005 For Dummies (2004)

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5.Click a radio button to tell AutoCAD what to do with the objects used to define the block: Retain them in place, Convert them into a block instance, or Delete them.

The default choice, Convert To Block, is usually the best. See Step 9 for a description of what happens with each choice.

6.Choose Create Icon From Block Geometry in the Preview Icon area.

Go ahead and create the icon; it will help you and others find the right block to use later.

7.Specify the Insert units to which the block will be scaled in the Drag- and-Drop Units drop-down menu.

When you or someone else drags the block from one drawing into another via the DesignCenter palette (see Chapter 4) or Tool Palette (described later in this chapter), the units you specify here and the units of the drawing you’re dragging into will control the default insertion scale factor.

8.Enter the block Description.

Now is the time to think like a database manager and enter a useful description that will identify the block to yourself and others.

9.Click OK to complete the block definition process.

If you typed the name of an existing block definition in Step 2, AutoCAD warns you that you’ll redefine that block definition. Click Yes to redefine, which will update all instances of the block in the current drawing to match the changed block definition.

AutoCAD stores the block definition in the current drawing’s block table. If you chose the Convert To Block radio button (the default) in Step 5, AutoCAD also creates a block insert pointing to the new block definition — the objects look the same on-screen, but now they’re an instance of the block rather than existing as separate objects. If you chose the Retain radio button, the objects remain in place but aren’t converted into a block insert — they stay individual objects with no connection to the new block definition. If you chose the Delete radio button, the objects disappear (but the block definition still gets created).

You can include in a block definition a special kind of variable text object called an attribute definition. When you insert a block that contains one or more attribute definitions, AutoCAD prompts you to fill in values for the text fields. Attributes are useful for variable title block information (sheet number, sheet title, and so on) and symbols that contain different codes or call-outs. I describe how to create and use attribute definitions later in this chapter.

Chapter 13: Playing Blocks and Rasteroids 301

BLOCK and WBLOCK

Keep your common symbol drawings in one or more specific folders that you set aside just for that purpose. You may want use one of the following techniques to develop a block library of symbols that you use frequently:

Create a separate DWG file for each symbol (using WBLOCK, or simply by drawing each one in a new drawing).

Store a bunch of symbols as block definitions in one drawing and use DesignCenter to import block definitions from this drawing when you need them.

Inserting blocks

AutoCAD provides a number of ways to insert a block, but the most commonly used and most flexible is the Insert dialog box. Here’s the procedure for inserting a block:

1.Set an appropriate layer current, as described in Chapter 4.

It’s a good idea to insert each block on a layer that has something to do with its geometry or purpose:

•If all the objects in the block definition reside on one layer, then it’s usually best to insert the block on that layer.

•If the block geometry spans several layers, choose one of them to insert the block on.

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If any of the block definition’s geometry was created on layer 0, then that geometry will inherit the color, linetype, and other object properties of the layer that you insert the block on. It’s like the chameleon changing color to match its surroundings or a politician changing his position to match the day’s opinion polls.

2.Click the Insert Block button on the Draw toolbar.

The Insert dialog box appears, as shown in Figure 13-3.

Figure 13-3:

The Insert dialog box.

3.Enter the block definition name or external filename by using one of the following methods:

•Use the Name drop-down list to select from a list of block definitions in the current drawing.

•Click the Browse button to select an external DWG file and have AutoCAD create a block definition from it.

You can use an external drawing to replace a block definition in your current drawing. If you click Browse and choose a file whose name matches the name of a block definition that’s already in your drawing, AutoCAD warns you and then updates the block definition in your drawing with the current contents of the external file. This process is called block redefinition, and as described in Steps 2 and 9 in the preceding section, AutoCAD automatically updates all the block inserts that point to the block definition.

4. Enter the insertion point, scale, and rotation angle of the block.

You can either click the Specify On-Screen check box in each area, to specify the parameters on-screen at the command prompt, or type the values you want in the Insertion Point, Scale, and Rotation text boxes.

Check the Uniform Scale check box to constrain the X, Y, and Z scaling parameters to the same value (which in almost all cases you want).

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If you need to modify a block definition after you’ve inserted one or more instances of it, use the REFEDIT command (Modify Xref and Block Editing Edit Reference In-Place). Look up “REFEDIT” in the AutoCAD online help system.

Attributes: Fill-in-the-blank blocks

You may think of attributes as the good (or bad) qualities of your significant other, but in AutoCAD, attributes are fill-in-the-blank text fields that you can add to your blocks. When you create a block definition and then insert it several times in a drawing, all the ordinary geometry (lines, circles, regular text strings, and so on) in all the instances are exactly identical. Attributes provide a little more flexibility in the form of text strings that can be different in each block insert.

For example, suppose that you frequently designate parts in your drawings by labeling them with a distinct number or letter in a circle for each part. If you want to create a block for this symbol, you can’t simply draw the number or letter as regular text using the mText or TEXT command. If you create a block definition with a regular text object (for example, the letter A), the text string will be the same in every instance of the block (always the letter A). That’s not much help in distinguishing the parts!

Instead, you create an attribute definition, which acts as a placeholder for a text string that can vary each time you insert the block. You include the attribute definition when you create the block definition (as I demonstrate in the “Creating block definitions” section earlier in this chapter). Then each time you insert the block, AutoCAD prompts you to fill in an attribute value for each attribute definition.

The AutoCAD documentation and dialog boxes often use the term attribute to refer indiscriminately to an attribute definition or an attribute value. I attribute a lot of the confusion about attributes to this sloppiness. Just remember that an attribute definition is the text field or placeholder in the block definition, while an attribute value is the specific text string that you type when you insert the block.

If you’ve worked with databases, the correspondences in Table 13-1 between AutoCAD objects (blocks and attributes) and database terminology may help you understand the concept.

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Attribute values can include AutoCAD 2005’s new automatically updating fields, such as date, filename, or system variable setting. Click the Insert Field button to the right of the Value text box to insert a field. See the “mText plays the field” section in Chapter 9 for more information.

4.In the Text Options area, specify the Justification, Text Style, Height, and Rotation.

The text properties for attribute definitions are the same as those for single-line text objects — see Chapter 9.

5.Choose the Pick Point button and choose an insertion point for the attribute definition.

An attribute definition’s insertion point is like a text string’s base point. Remember to use snap, object snap, or another precision tool if you want the eventual attribute values to be located at a precise point.

6.Click OK to create the attribute definition.

7.Repeat Steps 1 through 6 for any additional attribute definitions.

If you need to create a series of similar attribute definitions, create the first one using Steps 1 through 6. Then copy the first attribute definition and edit the copy with the Properties palette.

Block definition containing attribute definitions

After you create one or more attribute definitions — and any other geometry that you want to include in the block — you’re ready to create a block definition that contains them. Follow the steps in the section, “Creating block definitions,” earlier in this chapter.

At Step 4 in the section, “Creating block definitions,” select any attribute definitions first before you select the other geometry. Select each attribute definition one-by-one (clicking on each attribute definition rather than selecting multiple attributes with a selection window), in the order that you want the attribute value prompts to appear in the Enter/Edit Attributes dialog box (see Figure 13-5). If you don’t select the attributes one by one, your block and attributes will still work, but the order of the attribute prompts in the Enter/Edit Attributes dialog box may not be what you want.

You can use the Block Attribute Manager (choose Modify Object Attribute Block Attribute Manager) to reorder the attribute definitions in a block definition. You also can use this dialog box to edit other attribute definition settings, such as the prompt, text style, or layer. If you get tired of traversing four menu picks to get to this command, you can type the command name — BATTMAN (Block ATTribute MANager) — instead. I suppose it’s only a matter of time before Autodesk adds a ROBIN (ReOrder Block INsert) command. . . .

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shown in Figure 13-6. The most common attribute editing operation is to edit the text value — that is, the text string that appears in the block insert. You also can change properties of the attributes, such as layer and text style.

Figure 13-6:

The Enhanced Attribute Editor dialog box.

Many people use attributes in the way I’ve described so far — as fill-in-the- blank text fields in blocks. But attributes also can serve as data extraction tools. For example, you can export attribute values, such as part numbers and quantities, to a text, spreadsheet, or database file for analysis or reporting. The Attribute Extraction wizard (Tools Attribute Extraction) makes the process fairly straightforward. If you’re hungry to find out more, look up “EATTEXT (Enhanced ATTribute EXTtract) command” in the AutoCAD online help system.

Exploding blocks

The objects in each block insert act like a well-honed marching squadron: If you move or otherwise edit one object in the block insert, all objects move or change in the same way. Usually this cohesion is an advantage, but occasionally you need to break up the squadron in order to modify one object without affecting the others.

To explode a block insert into individual objects, click Explode (the firecracker button) on the Edit toolbar and then select the block insert. When you explode a block insert, AutoCAD replaces it with all the objects — lines, polylines, arcs, and so on — specified in the block definition. You then can edit the objects or perhaps use them to make more block definitions.

Don’t make a habit of exploding blocks cavalierly, especially if you’re working in someone else’s drawing and aren’t sure why the objects are organized as blocks. Most people use blocks for a reason, and if you go around exploding them left and right, you’re likely to be treated the same way that anyone who blows up a lot of things gets treated.