Expert Training

Creating block definitions

To create a block definition from objects in the current drawing, use the Block Definition dialog box. (The other way to create a block definition is by inserting another drawing file into your current drawing as a block, which I explain in the next section.) The following steps show you how to create a block definition using the Block Definition dialog box:

1. Click the Make Block button on the Draw toolbar.

2. TIP:Layers matter when creating the objects that makes up a block. Block geometry created on most layers retains the characteristics, such as color and linetype, of those layers. But if you create a block using geometry on Layer 0, that geometry has no characteristics, such as color and linetype of its own; chameleon-like, it takes on the features of the layer into which it’s inserted. (If you don’t know what a chameleon is, ask a zoology teacher or a politician.)

3. Type the block definition’s name in the Name text entry box.

   If you type the name of an existing block definition, AutoCAD replaces that block definition with the new group of objects you select. This process is called block redefinition. AutoCAD first warns you and then updates all instances of the block in the current drawing to match the changed block definition.

   Tip To see a list of the names of all the current blocks in your drawing, pull down the Name list.

4. Specify the base point, also known as the insertion point, of the block, using either of the following methods:

   • Enter the coordinates of the insertion point at the X, Y, and Z text boxes.

   • Click the Pick Point button and then select a point on the screen. (In this case, use an object snap or other precision technique, as described in Chapter 4, to grab a specific point on one of the block’s objects.)

   The base point is the point on the block by which you insert it later, as I describe in the next section.

   Tip Try to use a consistent point on the group of objects for the base point, such as the lower-left corner, so that you always know what to expect when you insert the block.

5. Click the Select Objects button and then select the objects that you want as part of the block.

6. 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, because it preserves the pointer to the block definition “recipe.” If you choose Retain instead, AutoCAD leaves the objects on the screen, but as separate objects with no relationship to the block definition.

7. Click a radio button to choose either Do Not Include An Icon or Create Icon From Block Geometry.

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

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

   If and when the block is dragged 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.

9. 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.

10. Click OK to complete the block definition process.

    If you don’t choose the Convert To Block or the Retain radio button, your objects disappear! AutoCAD has stored the block definition in the current drawing’s block table, however, and the block is ready to use. If you choose the Convert To Block radio button (the default), AutoCAD 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 choose 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.

Technical Stuff 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.

Tip 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.

   Remember 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.

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 redefining a block — it 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.

   Tip 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 do).

5. If you want AutoCAD to create a copy of the individual objects in the block instead of a block insert that points to the block definition, click the Explode check box.

6. Click OK.

7. If you checked Specify On-Screen for the insertion point, scale, or rotation angle, answer the prompts on the command line to specify these parameters.

After you insert a block, all the objects displayed in the block insert behave as a single object. When you select any object in the block insert, AutoCAD highlights all the objects in it.

Tip Another way to insert a block is to drag a DWG file’s name from Windows Explorer and drop it anywhere in the current drawing window. AutoCAD then prompts you to choose an insertion point and optionally change the default scale factor and rotation angle. Similarly, you can drag a block definition’s name from the Blocks section of the DesignCenter palette and drop it into the current drawing wi

ndow. (Chapter 4 describes DesignCenter.) New for 2004 AutoCAD 2004 provides one additional way of inserting blocks: the new Tool Palette, which is described in Chapter 2. As is true of using Tool Palette for hatching (Chapter 11), you first must create and configure appropriate tools — that is, swatches. The easiest method is right-clicking a drawing in DesignCenter and choosing Create Tool Palette. A new page is added to the Tool Palette area containing all of the block definitions from the drawing that you right-clicked. Simply click and drag a tool to insert its corresponding block into a drawing. As with hatching, you don’t get the chance to specify a different insertion scale. You also can’t use all of AutoCAD’s precision tools to specify the insertion point precisely, so you may need to move the block into place after inserting it. I recommend that you first master the other block insertion methods described in this chapter — especially the Insert dialog box and DesignCenter palette. Then, if you find yourself inserting the same blocks frequently, conside

r creating a Tool Palette containing them. See “tool palette tools, adding” in the AutoCAD online help system for more information.

Warning Be careful when inserting one drawing into another. If the host (or parent) drawing and the inserted (or child) drawing have different definitions for layers that share the same name, the objects in the child drawing takes on the layer characteristics of the parent drawing. For example, if you insert a drawing with lines on a layer called Walls that’s blue and dashed into a drawing with a layer called Walls that’s red and continuous, the inserted lines on the wall layer will turn red and continuous after they’re inserted. The same rules apply to linetypes, text styles, dimension styles, and block definitions that are nested inside the drawing you’re inserting.

Tip If you need to modify a block definition after you’ve inserted one or more instances of it, use the REFEDIT command (Modifyð Xref and Block EditðEdit 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 of the ordinary geometry (lines, circles, regular text strings, and so on) in all of 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). 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.

Warning 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 corresponde

nces in Table 13-1 between AutoCAD objects (blocks and attributes) and database terminology may help you understand the concept. Table 13-1: Attribute and Database Comparison AutoCAD Database

Block definition	Database table structure
Block insert	One record in the table
Attribute definition	Field name
Attribute value	Value of the field in one record

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.

Warning 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.

Warning If you explode a block that contains attributes, the attribute values change back to attribute definitions. This usually isn’t the sort of change that you want. If you really need to explode the block insert, you’ll probably want to erase the attribute definitions and draw regular text strings in their place.