May 10, 2011, 5:03 a.m.
posted by nuclear
In 3ds max, extrusion — in effect, pulling one shape out of another — is one of the three most common ways to create a 3D object from a 2D shape or spline. (Another is lathing, which I cover in the next section.) Extrusion involves dragging a 2D shape along a line perpendicular to the plane of the 2D shape. Imagine a circle. Now envision a line of a fixed length, starting at the center of the circle and perpendicular to the plane of the circle. Extruding the circle along that line would create a cylinder. In effect, a cylinder is an extruded circle; in this case, the perpendicular line is the axis of extrusion. (In some cases it’s called a path, but that’s another story.)
Most extrusions take place with the Pivot Point of the shape left at its default position. The Extrude operation is activated by selecting either Modifiers> Mesh Editing>Extrude from the Main Menu, or by clicking the Extrude tool in the Extrude Modifier under the Modeling tab on the Tab Panel.
Using either method will trigger the Extrude Parameters rollout in the Modify Command Panel, as shown in Figure.
The most important choices in this rollout are the Amount value, and whether Cap Start/Cap End are checked. The Amount value determines the height of the extruded object. Checking Cap Start or Cap End determines whether the object has a capped surface on either or both ends. The rest of the parameters can be left at their defaults until you get comfortable with these options.
Remember If you extrude a renderable spline, extrusion removes the rendered thickness. This also holds true if you Lathe a spline that has been set to renderable.
Extruded open shapes can be used as walls or ribbons in a 3D scene. Do the following to explore the creation of an open 2D shape or spline:
Choose Create>Shapes>Splines>Line in the Command Panel.
Create a wavy line in the Top Viewport. Do not close the shape.
Click the Extrude tool in the Modeling Tab of the Tab Panel.
The Extrusion Parameters appear in the Modifiers section of the Command Panel.
In the Command Panel, input a value of 25 for the Amount.
To get a good working sense of this operation, create a variety of open spline shapes and extrude them with different Amount values, as shown in Figure.
Most of the 2D splines you will transform into 3D objects by extrusion will be closed shapes. Extruding a closed spline creates a 3D object that appears to have volume. You can also create capped ends on a closed extruded spline. Try the following:
Choose Create>Shapes>Splines>Circle and create a circle in the Top Viewport.
Remember Make sure Renderable is switched off.
Click the Extrude Modifier in the Modeling Tab Panel.
Set the Amount of the Extrusion to 75 in the Command Panel.
Check Patch instead of Mesh to generate a different polygon arrangement.
Try this operation with Cap Start and Cap End on and off; you can see the results in the Perspective Viewport, as shown in Figure.
Extruding the helix shape creates a spiraling ribbonlike object. Cap Start/Cap End settings make no difference to the helix; it’s an open shape. The Amount value determines the thickness of the ribbon, as shown in Figure.
Figure: Compare this extruded helix object with the renderable helix object shown in Figure.