> > > About Round Placement References

The types of placement references that you select determine the types of rounds that you can create. The following list shows each reference type, and lists the round types that you can create using that reference type:
Edges or edge chains
Select one or more edges, or an edge chain.
The surfaces bordering the edge reference form the rolling tangent attachment for the round. The round propagates across tangent neighbors until it encounters a break in tangency. However, if you use a One-by-One chain, the round does not propagate across tangent neighbors.
Round types: Constant, Variable, Through Curve, and Full.
For a Full round, you convert two round pieces within a round set. The two edges must share a common surface.
Examples
Two edges 1. Edge reference
2. Round piece (with radius value)
Edge chain 1. Edge chain reference
2. Round piece (with radius value)
3. Existing round geometry
One surface and one edge
Select one surface first, and then one edge.
The round remains tangent to the surface. The edge reference does not maintain tangency.
Round types: Constant, Variable, and Full.
Example: Surface and edge 1. Surface reference
2. Edge reference
3. Round piece
Surface to Surface
Select two surfaces.
The edges of the round remain tangent to the reference surfaces.
Round types: Constant, Variable, Through Curve, and Full.
For a Full round, select a third surface as the driving surface. This surface determines the location and sometimes the size of the round.
Example: Two surfaces 1. Surface reference
2. Surface reference
3. Round piece (with radius value)