Blocks and XREFs

Blocks

One of the most useful features of AutoCAD (or any CADD software for that mater), is the ability to use "blocks." While you are working in a drawing file, you can "block" part of the drawing out and store this part within the same drawing file by using the "Block" command. This will allow later use of this block within the same drawing without having to redraw the same thing twice. It will also allow a change in the definition of the basic block which then gets reflected in every instance of this block in the drawing. The place where the "block" is stored we call "block heaven" as it cannot be seen on the drawing itself.

An example of the use of blocks would be if you need to draw many doors of the same size on a floor plan. You have the option of either drawing all five entities over and over again for each door (four lines and an arc), or drawing the complete door once and blocking it for reuse on all the others.

To make a block out of part of a drawing, do the following:

1. Type B<RET> Type the name you want to attach to the block after the words "Block Name" In the Dialogue box which appears on the screen. There is no limit to names you can give a block, as long as it is one word or number. Ideally, you should keep the names of the blocks simple and short, since you will have to type the name in again when you insert the blocks into the drawing.

2. Pick the "Select Point" button and then pick a location for the "insertion base point" (normally, the lower left hand corner of object you want to make a block out of). This is the should be OSNAPped to. The Insertion Point of a block can be thought of as a "handle" at which the block may be inserted later.

3. Pick the "Select Objects" button and then pick all the objects which you want to include as part of the block. Pick the "OK" button. Once this is done, the block is created and goes to "block heaven." Note that the "Retain Objects" check box is turned on (checked) by default. This means that the objects which you selected from the screen to include in the block will remain on the screen as the original lines, arcs, circles, text, etc. from which the block was formed. If that check box is unchecked, then the objects selected will disappear from the screen. In effect they will be erased, although they are made part of the new block. If that check box was unintentionally unchecked when you made the block and you want the objects back, type OOPS <RET> and they will be unerased. This last step is optional, and in fact may not be desirable, since these objects will look like the block, but will not be joined into a single entity as in the block itself. They remain

Copies of this block so-created can then be inserted only into this drawing.

HOW TO INSERT A BLOCK INTO YOUR DRAWING

Once you have a block created within the current drawing, you can bring it in by INSERTing it as one single unit in that same drawing as follows:

1. Type I<RET>. The Insert Dialogue Box will appear on the screen.

2. Click the Browse button and select the block you want to insert from the list, or browse for a DWG file on your drive.

3. Double click on the name of the block you want to insert from the list that appears on the screen. Pick the "OK" Button.

4. The command line will now prompt you for an "Insertion Point." What this means is where do you want the block to be inserted of placed in the current drawing. The point on the block you are inserting into your current drawing is called its "base," and is usually point 0,0. You can either type in x and y coordinates where you want the base point of this block to be located, or you can graphically "pick" a point on the current drawing with the cursor. You will see a ghost image of the block you are inserting ito the current drawing and can "drag" it into place if desired prior to picking the point of insertion.

5. At the next prompt, type the desired scale factor in the X direction <RET>. This is 1 by default, and generally that is what you would want.

6. At the next prompt, type the scale factor in the Y direction <RET> This is the same scale factor as the X-scale by default, and generally that is what you would want.

7. At the next prompt, type the desired rotation angle <RET>. This is 0 degrees by default which means that there is no rotation of the inserted drawing with relation to the original drawing=s rotation. That is also generally what you would want.

This will bring the block into the existing drawing as a "block" which can be treated as a single entity. The advantage of inserting a group of lines, arcs, and circles as a block is that the inserted block can be moved around, erased, scaled, mirrored, or copied by means of a single pick of the cursor, since it is now only one object, no matter how may lines, arcs, or circles it is made out of. The block will be inserted on the current layer, but its individual entities will be on their own native layers. For instance, if you insert a drawing file of a door which was created on the A-DOOR layer, you should insert it when the A-DOOR layer is current. If you inserted it when the A-WALL layer is current, the block will be located on the A-WALL layer, but its individual lines and arc will remain on the A-DOOR layer and they will not change color or linetype to that associated with the A-WALL layer. Therefore, if you were to freeze either the A-WALL layer or the A-DOOR layer, the block would not be visible. If you explode the block, the entities making it up will "float" back down to their native layers. If you were to create a block on the 0 layer, and then insert it, the block would take on the color and linetype characteristics of the current layer. The visibility of the block would be controlled only by the frozen or thawed state of the current layer, not the 0 layer. It is because of this unique characteristic of the 0 layer that it is also known as the "Chameleon layer."

The disadvantage of a block is that it cannot be edited within itself once it is inserted. "EXPLODE" the block using the EXPLODE command (X<RET>). This will reduce the block to the individual parts, lines, arcs, and circles from which it was made. You could also pre-explode it in the Insert dialogue box by clicking the Explode box in the lower left corner.

HOW TO COMBINE DRAWINGS

You can bring another existing drawing into your current drawing by a process called "INSERTing" one drawing into another. Since all drawings full size, there is no complication with differences in scale, which you may have in manual drafting techniques. To bring another existing drawing into to your current drawing , follow the steps below:

1. Pick from the Pull-down Menu: "Insert," then "Block...." The Insert Dialogue Box will appear on the screen.

2. Pick the "File" button.

3. Type the name of the drawing file you want to insert into your current drawing, or select it from the list which will appear on the screen. If you do not see the drawing on the list, you can double click on other drives or folders, in the usual "Windows" way.

4. Pick "OK."

5. If the drawing does exist and AutoCAD finds it, the command line will now prompt you for an "Insertion Point." What this means is where do you want the new drawing to be inserted of placed in the current drawing. The point on the drawing you are inserting into your current drawing is called its "base," and is usually point 0,0. You can either type in x and y coordinates where you want the base point of this drawing to be located, or you can graphically "pick" a point on the current drawing with the cursor. You will see a ghost image of the drawing you are inserting into the current drawing and can "drag" it into place if desired prior to picking the point of insertion.

6. At the next prompt, type the desired scale factor in the X direction <RET>. This is 1 by default, and generally that is what you would want.

7. At the next prompt, type the scale factor in the Y direction <RET> This is the same scale factor as the X-scale by default, and generally that is what you would want.

8. At the next prompt, type the desired rotation angle <RET>. This is 0 degrees by default which means that there is no rotation of the inserted drawing with relation to the original drawing=s rotation. That is also generally what you would want.

This will bring the new drawing into the existing drawing as a "block" which can be treated as a single entity. The advantage of the use of the inserted drawing as a block is that the inserted drawing block can be moved around, erased, scaled, mirrored, or copied by means of a single pick of the cursor, since it is now only one object, no matter how may lines, arcs, or circles it is made out of. The block will be inserted on the current layer, but its individual entities will be on their own native layers. For instance, if you insert a drawing file of a door which was created on the A-DOOR layer, you should insert it when the A-DOOR layer is current. If you inserted it when the A-WALL layer is current, the block will be located on the A-WALL layer, but its individual lines and arc will remain on the A-DOOR layer and they will not change color or linetype to that associated with the A-WALL layer. Therefore, if you were to freeze either the A-WALL layer or the A-DOOR layer, the block would not be visible. If you explode the block, the entities making it up will "float" back down to their native layers. If you were to create a block on the 0 layer, and then insert it, the block would take on the color and linetype characteristics of the current layer. The visibility of the block would be controlled only by the frozen or thawed state of the current layer, not the 0 layer. It is because of this unique characteristic of the 0 layer that it is also known as the "Chamelion layer."

The disadvantage of block is that it cannot be edited within itself once it is inserted. If this is desired there are two ways to accomplish this. One way is to "EXPLODE" the block using the EXPLODE command (the dynamite stick on the Toolbar). This will reduce the block to the individual parts, lines, arcs, and circles from which it was made. The second way is to INSERT the drawing as usual, but when prompted for a block name to insert, precede the filename with an asterisk (*) or check the "Explode" box on the Insert Dialogue Box. This type of pre-exploded block is called a "star" block, and will be inserted as the individual lines, arcs, and circles which originally made up the drawing.

XREFS

Another way to combine drawings is to use the "XREF" method. This makes use of an external reference to another drawing. To attach another drawing using this method, type

XR<RET>

Pick the "Attach" button.

The "Select Reference File" Dialogue box will appear. Find the drawing you want to attach on your computer and double-click on its name. You can change the folder or the drive to search for the file.

Remove the check mark from the box "Specify on screen." This will automatically position the XREF at the insertion point 0,0,0 and with a rotation angle of 0 (which is normally what you want).

The advantage of using XREFS instead of simply INSERTing a drawing file into the drawing you are working on is that whenever you open the drawing or plot the drawing, the updated and latest version of the attached drawing is shown within your drawing. These can be very useful for mechanical, electrical, and plumbing (so-called "MEP") drawings which would use the XREF of the architectural floor plan. Thus when the architectural floor plan changes, the MEP drawings will be automatically updated.

To allow automatic updating, you must have the XREF drawing on the same "path" (i.e., the same disk drive and sub-directory) on which it was originally attached.

HOW TO USE A BLOCK CREATED IN ONE DRAWING IN ANOTHER DRAWING

If you want to use the block created in one drawing in another drawing later on, you will have to make the block into a drawing file. This is done through the WBLOCK command. This command stands for "Write Block," which in effect is what you are doing. That is, you are "writing" the block into another new drawing file.

1. Type W<RET> (this is the alias for WBLOCK). This will bring up the Write Block dialogue box. Type in a filename and path of drawing file you want to create (this is the name you want to give to the soon-to-be-created drawing file). Do not add any filename extension. AutoCAD will automatically add a _.DWG filename extension to the file the same as any other drawing file.

2. Select the radio button "Block" under "Source" and type the name of the block you want to write to another file.

3. The block remains in the current drawing as a block and a copy of it is now translated to a normal drawing file complete with all layer, color, elevation, thickness, and linetype information.

HOW TO COPY A PORTION OF YOUR DRAWING TO ANOTHER DRAWING FILE

From time to time, you may want to save a part of the drawing you are working on to another file so that it may be used later outside of the current drawing. For instance, if you have just drawn an elaborate elevation of a double hung window, complete with trim, chances are you will want to do this again sometime later in another drawing or on another project, and you do not want to go through the lengthy exercise of doing it all over again. The process of saving a portion of your current drawing to another drawing is similar to WBLOCKing a block to a drawing file.

1. Type W<RET> (this is the alias for WBLOCK). Type in a filename and path of drawing file you want to create (this is the name you want to give to the soon-to-be-created drawing file). Do not add any filename extension. AutoCAD will automatically add a _.DWG filename extension to the file the same as any other drawing file.

2. Select the radio button "Objects" under "Source" and type the name of the block you want to write to another file.

3. Pick insertion base point from object (normally lower left corner)

4. Click the "Retain" radio button.

5. Click on "Select Objects" button and pick the objects you want to write to a file.

6. Click OK.