Rotating an 3D extrusion a certain number of degrees?

Question

Hello,
I'm trying to figure out how to rotate an extrusion a specific number of degrees. I can easily do it with Isometric views and the preprogrammed Off-Axis views. However, I just chose a random rotation.
In the example below, I made some stairs. Getting them to go in the opposite direction is easy - I just mirror the profile. However, I can't figure out how to properly rotate the stairs 90 degrees.
Does anyone know how to calculate these? I'm sure there's a way, but my brain can't get over it. I'm used to working in 3D modelling software where you can rotate based off a relative plane, not the fixed plane that Illustrator uses.  I've searched everywhere and can't seem to find this specific answer.
Thanks for any help,
Tien

Answer 1

I just chose a random rotation.
And that's the problem. In order to make sense out of this poorly-designed feature, you need to proceed in such a way as to keep a mental track of where you started and how you got to the orientation you decide upon.
This is because the three value fields do not reflect the rotations about the proxy cube's axes, which highlight with seemingly corresponding colors when you mouseover them (which would be far more intuitive and useful). Instead, they reflect the orientation of the invisible "virtual trackball" in which the proxy cube resides. So unless you can do trigonometry in your head as you drag things, the values are pretty much useless. Just yet another example of Illustrator's invariably unintuitive interface design.
Here is an example of how to proceed. It is not the only way for your example, but one way:
Before even starting with 3D Effect, I've reflected a copy of the blue staircase cross-section and colored it red. Then I grouped the two so as to manipulate them at once. Upon invoking the 3D Effect>Extrude & Bevel dialog, I set the dialog to Front, effectively zeroing the three values. In this orientation, the Z axis (extrusion depth) is along your line of sight.
Turn on the Preview checkbox. Click the cursor in the red value field, then tap the up/down arrow keys to increment the tilt of the "virtual trackball" to get the desired bird's-eye (or worm's-eye) elevation.
Mouseover the vertical axis of the proxy cube, so that it highlights green. Press and hold Shift. Tediously drag rightward until it looks like you have rotated the cube 45°. This is where you begin to encouter the hideous interface. Note that the value shown for the meaninglessly green icon is not 45°. You have to "eyeball" having arrived at the rotation that shows the left and right faces equally.
Okay the dialog. Copy the Group and Paste In Front. I've selected (white pointer) the pasted copies of the profiles and re-colored them just to differentiate them from the original pair.
Open the Appearance palette. DoubleClick the 3D Effect that is already applied to the copied Group. Its dialog opens with the same settings that you have already applied. Mouseover the rightmost vertical green axis of the cube and ShiftDrag it leftward until--again, eyeballing it--you have rotated it 90°. Note that the value shown for the stupidly green-colored icon now shows +40. Again, this is because the value shown is reflective of the axes of the "virtual trackball", not of the cube's axes. Clearly the difference between -40° and +40° is 80°, not 90°. But if you rotate the cube to a numerical difference of 90°, it will quite obviously not be a rotation of 90° about the vertical axes of the cube.
Note also that while you've done this, the blue value has changed. That's the value that the design of the interface suggests is supposed to correspond to rotation about your line of sight. And in fact, if you drag that outer ring, all it does is rotate the whole illustration, as if you were spinning the drawing board. But again, it is showing a rotated value, even though the cube does not appear to have been rotated in that way (i.e.; the green cube axes have remained vertical throughout). Again, this is because the values shown correspond to the useless "virtual trackball," rather than what you're actually interested in.
You can, by the way, directly manipulate the "virtual trackball" thusly: Mousedown in the black region outside the cube. Press and hold Shift. Drag up/down, left/right.
Typically hideous Illustrator interface design.
JET