Modeling with advanced techniques > 3D curves > Change the radius of a 3D circle or arc
  
Change the radius of a 3D circle or arc
You can change the radius of a 3D curve, circle, or arc.
To change a radius,
1. Click 3D Geometry and then, in the 3D Curve group, click Change Radius. The Change Radius dialog box opens.
2. Click Circ Edge and select the circular edge to modify.
3. Choose a Method:
Keep Vertex: The start and end vertices of the circle or arc are fixed.
Keep Center: The center of the circle or arc is fixed.
Keep Peak: The curve center (midpoint) of the circle or arc is fixed.
Keep Vert+Tng: The start or end vertex of the circle or arc and its tangent are fixed. The vertex closest to the spot where you selected the circle or arc is used.
4. Enter a New Radius or adjust the circle with your mouse in the viewport.
5. Click to complete the operation.
Methods
The following illustrations show how the Method affects a changed radius. The fixed points are indicated by red dots. The effect on an arc is shown with solid lines; the effect on a circle is dotted.
Vertex
The start and end vertices of the circle or arc are fixed.
Center
The center of the circle or arc is fixed.
Peak
The curve center (midpoint) of the circle or arc is fixed.
Vert+Tng
The start or end vertex of the circle or arc and its tangent are fixed.