Smoothing blends edges between faces to produce a smooth curved surface. You can control how smoothing is applied to a surface so your objects can have both smooth surfaces and sharp faceted edges.
Smoothing is controlled by smoothing groups, which are integers from 1 to 32. Whether edges display between adjacent faces depends on whether the faces share a common smoothing group.
If faces have no smoothing groups in common, the faces have an edge between them.
If faces have at least one smoothing group in common, the edge between the faces is smoothed.
Because each face has three edges, only three smoothing groups can be in effect for any face. Extra smoothing groups assigned to a face are ignored.
Do one of the following to view or change smoothing group assignments:
Turn on the Smooth check box on the Parameters rollout of a parametric object to set default smoothing for the object.
Apply a Smooth modifier. If a Face sub-object selection is active, Smooth applies to the selected faces. If no faces are selected, Smooth applies to the entire object.
Apply an Edit Mesh modifier, enable Face (or Polygon or Element) sub-object mode, then use the features on the Surface Properties rollout.
Convert the object to an editable mesh, enable Face (or Polygon or Element) sub-object mode, then use the features on the Surface Properties rollout.
The easiest way to view smoothing is to look at an object in a shaded viewport. In this case, you are not viewing the smoothing groups but rather their effect on the shaded surface.
You can see the smoothing group numbers for selected faces by looking at the Smoothing Group buttons on the Surface Properties rollout of an editable mesh object or the Edit Mesh modifier.
Smoothing Group buttons appear as follows:
Group numbers not used by any face in the selection, appear normal.
Group numbers used by all faces in the selection, appear selected.
Group numbers used by some, but not all, faces in the selection, appear blank.
Click Auto Smooth to assign smoothing automatically. You set a Threshold angle to determine whether to smooth adjacent faces.
If the angle between face normals is less than or equal to the threshold, the faces are assigned to a common smoothing group.
If the angle between face normals is greater than the threshold, the faces are assigned to separate groups.
Auto Smooth is found on the Surface Properties rollout and on the Smooth modifier.
You manually assign smoothing groups to a selection of faces by clicking Smoothing Group buttons on the Surface Properties rollout or the Smooth modifier. The smoothing group of each button you click is assigned to the selection.
You can also select faces according to the assigned smoothing groups. Click Select by Smooth Group on the Surface Properties rollout and then click the smoothing group of the faces you want to select.
This is a convenient way to examine smoothing groups on an object someone else created.