Assignment
Create a hollow round-to-rectangular duct standing along +Z. At z=0 outer opening is a diameter 40 circle; at z=70 outer opening is a centered 60 x 30 rounded rectangle, corner radius 5. Both opening centers at x=y=0. Use a smooth continuous loft between profiles; open at both ends. The inner loft joins a diameter 36 circle at z=0 to a 56 x 26 rounded rectangle, corner radius 3 at z=70. Define the wall by the difference of these two lofts (constant normal thickness along the entire loft is not required). Add an annular flange outer diameter 54, inner diameter 36, z=0..4, with four diameter 4 through holes on radius 23 at 45,135,225,315 degrees. Export a single watertight STEP solid and STL. End-profile length tolerance 0.1 mm.
