LT On-line: Lesson 7

Another trip around the block

Page 1: Explode Blocks

My previous LT Online tutorial covered how to define and insert blocks. After you're comfortable with basic block creation and insertion, you'll want to know how to perform additional block operations. I'll teach you how to explode blocks (and when not to), how to transfer them between drawings, and how to redefine them in one or more drawings.

The procedures described here work with AutoCAD LT 2000 and AutoCAD 2000. Most of the procedures are similar in AutoCAD LT 98 and AutoCAD Release 14, but the dialog boxes look a little different.

I've provided a sample drawing file, LOTS-O-SCREWS.DWG, to make it easy for you to experiment with the procedures described in this tutorial.

How to explode blocks
All objects in a 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 and not affect the others.

To explode a block insert into individual objects:

1. Select Explode (the firecracker button) on the Edit toolbar. AutoCAD starts the Explode command and prompts you to select objects.

Figure 1.

2. Select one or more block inserts. For example, pick one or more of the screws in the sample drawing LOTS-O-SCREWS.DWG.

3. Press Enter. Figure 1 shows the results of exploding one of the screw block inserts.

When you explode a block insert, AutoCAD LT replaces it with all the objects-lines, polylines, arcs, and so on-specified in the block definition. You may not see any immediate difference on the screen, but when you select objects for editing, you'll notice that what used to be a group of objects that behaved as a unit now act as individual objects. You can edit the objects individually or perhaps use them to make more block definitions.

In cases such as with the screws in LOTS-O-SCREWS.DWG, you'll notice a difference-objects may change color or linetype. That's because the objects were defined on layer 0, which is the chameleon layer for block objects (see August's tutorial for more information).When you insert a block that contains objects that were drawn originally on layer 0, those objects inherit the color and linetype properties of the layer that's current when you perform the insertion. When you explode the block insert, the objects change back to layer 0.

When not to explode blocks
Don't make a habit of exploding block inserts, especially if you work in someone else's drawing and aren't sure why the objects are organized as blocks.

In particular, you shouldn't explode a block insert that contains attributes (learn about attributes in next month's tutorial). To see why not, explode one of the circles with a number in it in LOTS-O-SCREWS.DWG. The text contained in the attribute is replaced by an inscrutable attribute definition name.

If you're not sure whether a block contains attributes, choose Modify|Object|Attribute|Single and click on the block insert. If the Command line reports That block has no editable attributes, then the block insert probably contains no attributes (there are some obscure exceptions that I won't address here). If instead you see an Edit Attributes dialog box, then the block insert contains attributes and you shouldn't explode it.

If you explode a block insert and immediately realize that you shouldn't have, simply click the Undo button on the Standard toolbar.

Another trip around the block
  Page 1: Explode Blocks
  Page 2: How to transfer blocks between drawings
  Page 3: Redefine blocks