Autocad R8 (2.8) and higher versions

Those who make drawing in 3D by AutoCAD may want to rotate objects also out of Z axis. Most of us try to do this by changing UCS. However, it is a very laborious work to change UCS first and then use ROTATE command and change UCS back to its original. For this reason, AutoCAD introduced a new command named as 3DROTATE. Now, let’s take a close look at this command together…:

Fig. 1

In Fig. 1, our final aim is to draw the half bowl on the right side. Each user determines a different drawing strategy for each drawing. Here, we will first start by drawing a half circle to any location, and then use ROTATE3D command to rotate it in upwards direction. After doing this, we will draw an axis line and make a half tour for our arc around this axis. Now, you draw the horizontal arc and axis lines. And then, let’s apply ROTATE3D command together.

Command: 3DROTATE
Current positive angle: ANGDIR=counterclockwise ANGBASE=0

As we will mostly deal with angles, AutoCAD will give us information about current angle direction (ANGDIR) and current starting angle (ANGBASE). Right handle rules, which we are already familiar from vectors in physics, are also adopted by the engineers who made AutoCAD. While thumb of your right hand show the axis direction, keep your remaining fingers as if you are holding something, so these fingers will show the rotation direction.

Fig. 2

Select objects:
Specify first point on axis or define axis by
[Object/Last/View/Xaxis/Yaxis/Zaxis/2points]: 2p

Before converting our arc into half bowl, we have to bring it to upwards direction. In order to do this, we have to rotate our arc around 1-2 axis (Fig.1). As it can be seen, AutoCAD offers us many options for defining axis. As I am familiar with the right hand rule, my favorite is always 2 points. If we look at right hand rule in Fig. 2, if we select 1-2 axis line first from ends no.1 and later no.2; then, while our thumb is pointing point 2, our other fingers will show + (plus) rotation direction.

Specify first point on axis : [1]
Specify second point on axis : [2]
Specify rotation angle or [Reference] : 90

When the command is completed, then our arc will be upwards. Before this stage, we will need an aiding line in Z direction as a rotation axis. This line is marked with red in Fig. 1. Final command that we will use is REVSURF. This command revolves any entity around any axis selected.

Command : REVSRURF
Select object to revolve : (select our line here)
Select object to define axis of revolution : (select red line here)
Specify start angle <0> :
Specify included angle (+=ccv, -=cw) <360> : 180

Answer of this prompt is 180 degree. If we have drawn the red axis line from up to down ( as there is no aiding line, it will be very hard in this example ), then our bowl would be exact mirror copy of bowl shown in Fig. 1.

Related articles:

• 3DALIGN

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Last read: 28 August 2008, 8:17

3D, Autocad, Command, Modify