I am trying to model a surface that will be cut by a cylindrical tool swept along an unknown path (think plunge cutting with a key cutter while moving in X and Y). I know the location where the tool's edges must enter and exit the part, and I know the diameter of the tool. Given this information, I can sketch a cross section at any point along the path, but when I try to use a feature to get the surface into 3D,  it creates an inconsistent curvature surface. I have tried sweeps, lofts, and boundary surfaces, to no avail. Ideally I could sweep a solid to account for the thickness of the tool, but I am unsure if even the basic premise is possible. The pictures show the overall model, the body with the entry and exit edges shown, and the resulting surface from one of my attempts. Thank you in advance for all your help!