Wednesday

Understanding UCS (Part 3)

Post a Comment Oct-15-2008 | Posted by Erhan Toker | Printable Version | Level |

In this article, will see how we can use UCS to draw on randomly inclined surfaces.

Fig.1

The WEDGE we see in Fig.1, has a surface that is neither paralel nor perpendicular to the horizontal plane, which means that we can’t use any of the predefined settings for UCS. Dynamic UCS on the other hand, onlt interacts with the center point of the surface and can be annoying at times. We will learn the “3-points” function of the UCS, which is arguably the most useful way.

Fig.2

There is an easily accessable panel in the RIBBON menu in AutoCAD 2009. We can run the “3-point” option from the button here. Using the command promt is pretty simple too.

Command: UCS
Current ucs name: *WORLD*
Specify origin of UCS or [Face/NAmed/OBject/Previous/View/World/X/Y/Z/ZAxis] [World]: 3

As I’ve said earlier, altough some sub-functions don’t show up in the command prompt, they can stil be used.

With the “3-point” option, you have to specify the origin, the direction of the X-axis and then the direction Y-axis by specifying three points.

Specify new origin point [0,0,0]: [1]
Specify point on positive portion of X-axis [1.0000,0.0000,0.0000]: [2]
Specify point on positive-Y portion of the UCS XY plane [0.0000,1.0000,0.0000]: [3]

Fig.3

You will now see that the UCS icon now shows the same plane as the inclined face of our wedge, just like in Fig.3. AutoCAD 2009 users will also see that the “View Cube” has also changed, like in Fig.4.

Fig.4

You will see that top, left, right and other orthographic functions hae been redefined to work with the new UCS. Let’s draw a cylinder from the center of the face.

Fig.5

While specifying points fort he cylinder, you will notice that the UCS now Works on that plane. This is one of the greatest features that AutoCAD has to make 3D modeling simpler and faster. Once you change the UCS, your coordinate system will change too. In my example, I specified the lowe left corner of the wedge as the origin point. You can now use coorinate inputs while working on this face.

!Note! : When the UCS changes, commands like PLAN, VIEWPOINT and UCS also adjust themselves accordingly. In my example, the PLAN command gives me a result like in Fig.6.

Fig.6

!Note’: Whenever you adjust the UCS settings, the current UCS will be reffered to as “unnamed” while the previous one will be called “previous”. It is possible to bring back the previous settings. Note that you cannot take the UCS back several steps. You have to name the various UCS settings if you will be using several custom UCS settings in a drawing. I will talk about the naming of UCS settings in the final article of this series.

We learned how the “3-point” function works. In the next article we will see how rotate the UCS about an axis.

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