Thursday

Understanding UCS (Part 2)

In my first article, I wrote about rotating the UCS about an axis and the use of the UCS command in 2D drawings. From this article on, we will learn about the 3D applications of the UCS command. Let’s examine the various directions on a cube before we go further, in Fig.1.

Fig. 1

Well the figure itself is pretty much self explanatory.. AutoCAD 2009 users will enjoy easier access to these various views through the use of the View Cube, Fig. 2 .

Fig. 2

With the View Cube feature, you can have an easier understanding of your current view, the available views and your orientation. The cube comes with the predefined views written on the respective facets of the cube, and you also have a mini UCS drop down menu right under the cube.

Now let’s try to draw a cylinder lying on the cube that we had drawn earlier. You have to set the UCS on  the “front” face of the cube to be able to draw the wanted cylinder. See how the command works:

Command: UCS
Current ucs name: *NO NAME*
Specify origin of UCS or [Face/NAmed/OBject/Previous/View/World/X/Y/Z/ZAxis]<World>: FR

Although we see only a number of options available for the UCS command, you can in fact enter many values for it. Simply enter FR to specify the FRont plane. While this is not among the options, it is accepted as one of the default values and the necessary arrangements are made, Fig.3 .

Fig. 3

As you can see, the Z axis is arranged so that we can draw the heigth of objects perpendicular to the front plane. The base of objects will be on the front plane (XY plane) while they will rise in height along Z axis. We can easily draw a cylinder on our cube as in Fig. 4.

Fig. 4

It is ideal to use the UCS command for cubes, walls or facedes of buildings. You can access these settings using the UCSMAN command in AutoCAD 2009, Fig 5.

Fig. 5

It is easier to access them on earlier versions through the UCS II toolbar, Fig. 6.

Fig. 6

If you are using 2008 or higher, and you have the Dynamic UCS feature enabled, you may not have to play with UCS settings at all, for simple shapes and faces. The UCS can become parallell to a face if you are trying to draw in the middle of that face, Fig.7.

Fig. 7

I tried talking about orthographic UCS in this article. More complex surfaces will be covered in another article.