Dimensions

Dimensioning is to take measurements and then show them on the figure. AutoCAD offers the user to take dimensions in a variety of ways. One can dimension objects such as a line or polyline or between two points. Dimensions can be horizontal, vertical, aligned, rotated, ordinate, baseline or continued.

AutoCAD basically offers three types of dimensions, namely linear, radial and angular. Dimension when taken, have the same settings as that of the dimension style set. Hence they take on a particular arrowhead style, text location and lateral tolerances.

The following figure gives an example of the dimensions that can be taken. The dimensions have been taken of the jaw and are linear, radial and angular.

Coordinate Systems (UCS & WCS)

AutoCAD uses two coordinate systems:

• World Coordinate System (WCS)
  
  In this type of a coordinate system, the X axis is horizontal, the Y axis is vertical and the Z axis is at 90 degrees to the plane formed by the X and Y axis. The origin is the intersection point of the X and Y axis, i.e. (0,0), which is always at the left bottom side of the drawing.
  
• User Coordinate System (UCS)
  
  To facilitate changes in direction of the plane that one is working in, the UCS has been developed. The direction can be seen in the form of a grid by pressing F7. The UCS is defined in terms of the WCS

The UCS can be relocated in the following ways:

o By defining a new origin
o Rotating the UCS around any one of the axis. That is, the direction of one of the axis is fixed while the other two are interchanged.
o Loading a saved UCS
o Specifying the direction in the direction of the present view or by aligning it with an object

Once the UCS has been relocated, Snap, Grid, and Ortho modes all rotate in line with the new UCS.

Copy

In copy, images of the original objects are created at a specified distance from the original. Procedure similar to Move is applied here i.e. distance in the form of a point (base point) and the second point is specified. Direction is also given to place the object in the desired location.

Move

Objects can be moved without changing their size or orientation. When combined with object snaps, these objects can be relocated precisely where the requirement is.

There are basically two ways to move an object. Both of them however require that the Move command be chosen or it be typed in the command line.
· In the first one the object to be moved is selected. The base point of movement is then selected followed by the point of displacement.
· In the second method, the object that is to be move is again selected first. Coordinate values for the first point and second point of displacement are then given. Pressing ENTER then moves the object by using the relative displacement.

This command should not be confused with offset, which is also very similar.

Union Command

Union is a command that combines two or more objects to form one single object. The volume of the final object includes the volume of all the selected objects and its area encloses the area of all regions in a subset.

To apply this command, it must be written in the command line, after which the objects should be selected. Finally, ENTER is pressed for the result. The example explains this process. Two separate regions, 1 & 2, are to be unified. The procedure is followed and the end result is a single fused region

Subtract Command

Subtract command, as the name implies, subtracts one object from another. To be precise it subtracts the second selected objected from the first selected object. The result is that a new object is created.

One condition of subtraction is that both the

objects must be on the same plane. However, if the subtraction is performed simultaneously regions on different planes can also be subtracted.

Subtraction can be applied to both 2D and 3D figures.

The example shows that a cylinder has been subtracted from the object that was created in the Extrude Command topic

Extrude Command

Once a 2D region is obtained, it can easily be converted into a 3D object by the Extrude command. The height value, tapered angle and the planar face need to be specified.

For explanation purposes, work is continued on the region created in the Region Command topic and it is extended from a 2D region to a 3D object.