BLOCKS

In this lesson you will be introduced to blocks. By definition, a BLOCK is a collection of simple entities (lines, arcs, circles, text, etc.) that form a more complex entity that normally represents an object in the real world, e.g. a door, a chair, a window, a computer.

There are many advantages to using blocks, here the major ones:

• Blocks are a single entity. This means that you can modify (move, copy, rotate) a block by selecting only one object in it.

• You can build up a library of blocks consisting of the parts that you require many times in your workday. These blocks can be stored in a separate folder and even on a network so that all drafters have access to them.

• Using blocks can help keep your file size down. AutoCAD stores block definitions in its database. When you insert a block, AutoCAD only stores the name of the block, its location (insertion point), scale and rotation. This can be very noticeable in large drawing.

• If you need to change something, you can redefine a block. For example, you draw a chair and turn it into a block. Later, you're told that the size of the chair has changed. Since you used a block you can redefine the block and all of your chairs are updated automatically. If you had drawn (or copied) 100 chairs in your drawing, you would have to manually change each one.

• Blocks can also contain non-graphical information. This means text objects called attributes. For example, you have made blocks of different chairs. You can add information to the block such manufacturer, cost, weight, etc. This information stays with the block, but can also be extracted to a database or spreadsheet. This would be useful for things such as a bill of materials. Attributes can also be visible or invisible in your drawing. Another good use of attributes could be a title block.

• You can even easily add internet hyperlinks to blocks so you can connect a block to a page on a supplier's online catalog.

There are two types of blocks you can create: blocks that are internal to your current drawing, and those that are external, or saved as a separate file. To create the different types, different commands are used.

Here are the commands that you will need for using blocks in this lesson:

For this assignment, you will be using any one of the floor plans you drew earlier in Lesson 2-1.

Open the drawing.

Zoom in to one section of the room close to a desk.

Create a new layer called COMPUTERS (remember LA invokes the Layer Properties Manager) and make that layer current.

Draw the computer as shown below. You do not have do dimension it.

Start the BLOCK command by either typing B or using the pull down menu or the icon. You will see a dialog box that looks like the one shown (some versions of AutoCAD will have a slightly different dialog box (with different options). Enter information the same way though.

1 : The first thing that you want to do is give your block a name. Type COMPUTER in the edit box beside Block Name.

2 : Now you need to select an insertion/base point. Pick the Pick Point button and then pick the midpoint of the bottom line. Make sure that the retain button is selected (this will keep your objects on the screen as individual objects.

3 : Next you want to select the objects for your block. Pick the Select Objects button and then select all the parts of your computer and press <ENTER>.

4 : Now select the drawing units you used to create the original objects in.

5 : This is optional, but you can add a description here. This is good if you are creating specific parts, like maybe a motor and want to add some quick specifications.

6 : Pick the OK Button and the dialog box closes. It will look like nothing happened, but the drawing file now has a "Block Definition" for a Computer in it. Congratulations, you have created your first block.

Now that you have created a block, it's time to insert it. Start the Insert command by typing I <ENTER>. You will see this dialog box on the screen:

By default, all the options you need are pre-selected. Since you only have one block in your drawing, its name is displayed.

Make sure that the Insertion Point - Specify On-screen box is checked, and the Explode button is not checked. The Scale - Specify On-screen should not be checked. Then press the OK button. Pick anywhere on your screen and you will see the block appear.

Now insert a computer on every desk in your drawing. You can also copy the block instead of re-inserting each time, but make sure you know how to insert.

Copy the drawing below of the chair.

This time you will be creating an external block using the wblock command. This difference here is that the block will become a separate, external drawing file for use in other CAD drawings.

In the dialog box below, you will see that you have almost all the same options. Instead of giving the block a name like you did before, you give it a filename in a specific folder.

Make sure you put the block in a logical path and give it a good, descriptive name.

When you insert an external block, use the same Insert command that you did above and use the Browse button to navigate to the folder where you stored your block. Insert it like you did before. Put some chairs in front of the desks in your drawings, and rotate them if needed.

Now you have created two blocks. The process is the same for any other block that you need to create from drawing objects.

If you want more practice, draw more objects and create blocks from their geometry.

If you want to see how to update a block, modify the computer block by stretching the monitor portion at the top down by 8". Now create a new block using the same COMPUTER name. After re-defining the block, all your computer blocks in the drawing will update to the new definition.

This is a good example of how blocks save you time. In a typical work situation, the original specifications for the computer could have changed from large CRT monitors to flat screens and you would need to change them all. Using blocks is much easier than changing each individual object one at a time.

Remember that blocks are powerful tools for the reasons listed above. In any discipline of CAD drafting, you will use them.