A block in Autocad
is a collection of all of the line and arc entities that
create an object, 'moulded' together to make one selectable
object. Selecting one particular entity (such as a midpoint
of a line for example) will select all objects contained
within the block. They can be moved, rotated, mirrored etc
and will always be treated by Autocad as one whole object.
The only way to 'break' the block apart, and split it into
its seperate line entities, is to explode it. If one particular
part of a block needs to be changed, the block has to be
exploded, the modification made, and the objects created
back into a block.
Blocks are an invaluable way of quickly arranging complex
pieces of a drawing. Selecting the object is a breeze, it
is no longer neccessary to painstakingly select each indivdual
line. They also prevent accidental modification of parts
of the object, as they cannot be modified unless the whole
block has been exploded. Blocks also make it easy to duplicate
the same object throughout a drawing, and as Autocad recognises
that each copy of a block is identical to the previous,
the memory & processing time required byAutocad is reduced.
The most impressive feature of blocks is that if a block
detail has to be amended, simply changing the detail and
'redefining' the block applies the changes to EVERY instance
of the block in the drawing!
A simple example
of the use of blocks is in a plan view of a classroom measuring
5.5m x 5.5m. You may be required to find the most suitable
layout for 12 desks and 24 chairs. You would of course have
to draw the chair and table. Then simply turn them each
into a block. They can then be moved, selected and copied
simply and quickly.
1) Download the
drawing file for your version of Autocad.
Autocad 2000 .dwg file
r14.dwg Autocad 14 .dwg file
2) Firstly we'll turn the table into a block. To open the
'block definition' box type the command block
into the Autocad console then hit
3) We'll need to name the new block that we create. Type
the name box.
Click the select objects button to select the seperate entities
that we wish to contain within the block. Select all lines
making the table then right-click
or hit enter to return to the block
definition box. Within the objects section we have 3 options
to choose from: Retain,
Convert to Block
Once the OK button is hit, the block
will be created and stored within the drawing, although
the selected entities will not have been turned into the
block and will be kept as seperate entities. The block can
be inserted from the 'insert -> block ' drop down menu.
to Block: This is the opposite
of retain, the selected entitiles will be converted into
a block, and will be the first instance of the block within
Not as drastic as it sounds! The block
will be created, although not displayed. The seperate entities
which make the block will be deleted. The block can be inserted
from the 'insert -> block ' drop down menu.
In this instance, choose convert
Now we hace to choose a base point for the block. This is
simply the insertion point if we decide later to insert
the block from insert-> block in the drop down menus.
Choose a suitable position, such as the approximate centre
of the table, or the midpoint of one of the lengths. Right-click
or hit enter to return to the block
Preview Icon simply lets you choose if you want Autocad
to create a small preview of the block which will be shown
in the insert block box. This function is useful if a large
amount of blocks are to be created within a drawing. Whichever
option is chosen does not affect the block creation, so
choose whichever option you prefer!
Insert units should be set to whichever scale we you are
drawing in. This drawing is using 1 Autocad unit to represent
1mm, so select millimetres from the drop down box. An optional
description of the block can be entered, if desired.
That's it! Hit OK
to create the block. Try selecting the table, notice how
the entire table becomes selected? Also note that the colour
and linetype of any of the lines within the table cannot
turn the drawing of the chair into a block
using the block command, name the block: chair, and use
the convert to block
that we have the chair and table block, lets see how simple
it is to work with blocks.
Copy the chair and place the copy to the right of the existing
chair, so that that there are two chairs behind the table.
how we said we would arrange the 12 tables and 24 chairs
to fit into the room? Lets arrange them by making copies
of the original blocks. It would be acceptable to use the
copy command to make copies, although it may be a little
tiresome to arrange them neatly. By far the quickest way
is by using the Array command we looked into in Tutorial
an offset of 1500mm for the row and column offsets, and
array to 4 rows and 3 columns as shown below.
The finished result:
Imagine that the school decides that the chairs aren't to
have arms! All of the chairs can be amended by simply exploding
1 chair, modifying it then saving back to the block usig
the SAME block name:
1) Zoom in on
one of the chairs, and explode it. This will break the block.
2) Delete the
arms of the chair, as below.
3) Now use the
to turn the 'armless' chair back into a block. Make sure
that you use the same block name as the existing block to
be changed, for block redefine to work correctly.
4) Autocad will
warn you: 'Chair is already defined. Do you want to redefine
it?'. Choose Yes.
Voila! Every instance
of the chair has now been changed by redefining the block.
This is where the power of creating blocks really comes
into its own.
are copying the same information around in a drawing, always
ensure that you have turned it into a block first, it can
save a lot of headache when you later decide to alter the
any errors/omissions to
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