1. Create circle Sweept. Use Center & Radius as subtype, Buondary.1 as center curves. Radius =20mm
2. Use Circle Sweept to split surfaces Extrude.1 & Extrude.2. Define Sweept.1 as cutting element.
3. Result after split operation.
4. Hide sweep.1 surfaces.
5. Create Blend between Split.1 & Split.2.
6. Click OK to see Blend surfaces.
7. Show swept.1 surfaces to edit radius value.
8. Change radius value to 30mm to modified blends offset distance.
9. Click OK to close Swept definition & update the blends.