Cinema 4D / BodyPaint 3D Program Documentation Tutorials Mechanical Modeling Tutorial Modeling with Splines and Generator Objects
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Lathe Object

Numerous axially symmetrical objects can be created by rotating a profile shape around their axes. Some examples are drinking glasses, bottles, a winding staircase or even a snail’s shell. These shapes can be created using the Lathe object in conjunction with a Spline object. In our example we will create a Linear Spline object in the front Viewport (XY view) and use the world coordinate system’s Y axis as the symmetry axis. Start by creating a Spline, as shown in the image below.

Creating an outline

You can either create the outline manually or first create the outer line and use the Create Outline function (Mesh | Spline). When using the latter method simply select the function and click + drag in the Viewport to create the outline. The Distance value can be defined manually for more exact placement. When creating a Spline, the axis symbol may lie in the way of placing a point. The axis symbol can be turned on or off by pressing Alt + d on your keyboard. Since we will be rotating this Spline around the Y axis to create our object, its inner points must lie precisely on the symmetry axis. Select each point separately and set its X position to 0 in the Coordinate Manager, as shown at the center of the image below. Select the two center points at the right of the object, as shown at the right of the image below, and give them a soft interpolation via the Soft Interpolation command (Mesh | Spline). This will automatically add tangents to these points that can be used to create a rounded curve. The Soft Interpolation command can also be accessed from the menu that appears when you click with the right mouse button in an empty part of the Viewport.

Chamfering points

These points can be further edited by dragging the handles at the end of each tangent. If you want to create a small curvature, using the Chamfer function would be the best option. To do so, select the points you want to chamfer and select the Chamfer tool’s Radius value in the Attribute Manager (Mesh | Spline or right-click in the Viewport). The curvature’s radius can also be defined manually via the Chamfer tool’s Radius value in the Attribute Manager. Select the points and modify them, as shown in the image below. We recommend manually entering a Radius value since it can be easy to inadvertently add unwanted chamfers when using the mouse.

Controlling subdivision

Once you have shaped the Spline to fit your needs, create a Lathe from the Create | Generators menu and make the Spline object a Child object of the Lathe object in the Object Manager. At the right of the image above you can see the result. A pretty bulky object has been created that can be modified via the Spline points. The Lathe object object will automatically maintain the voluminous shape.

The overall shape of the object will be influence by the location and number of Spline points and by the Subdivision value. In the image below you can see how the level of detail is increased when the Angle option is set from Adaptive to Subdivided mode. Increasing the Angle value will reduce the number of surfaces at the small chamfers to a reasonable number.

In the next image you can see how the Lathe object object’s Subdivision value can be used to increase the number of surfaces that run in the direction of rotation.

Creating unusual shapes

Often, shapes must be modeled that are not closed or comprised of simple rotation objects, e.g., a baking form or the rail of a spiral staircase. This is something the Lathe object can handle as well. The Angle value can be used to generate rotations of less than 360°, as shown in the image below. At the left of the image you can still see the open endings of our Spline Object - no cap surfaces were generated. This can be corrected by simply closing our Spline object. To do so, simply enable the Spline object’s Close Spline option in the Attribute Manager. How to fine-tune the Generator object’s caps surfaces and edges was already explained above.

The Lathe object Movement value can be used to offset the Spline during rotation. Entering an Angle value of greater (even far greater) than 360° can result in interesting shapes being created, as shown in the image below. The Scaling value can also be used to modify the scale of the Spline shape in the course of the rotation. These methods can be used to, for example, model a snail’s shell or a screw.

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