Hi,
are you looking for something like this?
Show[RevolutionPlot3D[12 - x^3, {x, -2, 2}, {theta, 0, 2 Pi},
RevolutionAxis -> {1, 0, 0}, AspectRatio -> 1],
RevolutionPlot3D[12 - 4 x, {x, -2, 2}, {theta, 0, 2 Pi},
RevolutionAxis -> {1, 0, 0}, AspectRatio -> 1]]
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M.