The media attached below is the bottom/top view of drilled sphere. If you look it from sideways, you'll see that the drilled hole is in the form of cylindrical shape. So, Volume of the drilled shape= volume of cylinder = πr²h, where h is 2r. ∴Volume of cylinder(V1) = πr²(2r) = 2πr³. Volume of sphere(V2) = 4πr³/3. Therefore volume of remaining metal bead = V1 - V2 = 2πr³ - 4πr³/3 = (6πr³ - 4πr³)/3 = 2πr³/3.