EN: In 3D modeling CAD users often face problems that can be success-fully analyzed and solved only by the methods of Descriptive Geometry. One such problem is considered in this paper: the construction of structural elements of machine parts known as stiffening ribs. In addition, a possible geometry of ribs is analyzed and a review is performed of tools for its modeling available in up-to-date CAD packages. Some features are shown that are useful
in representing parts with ribs in technical drawing manuals. An innovative approach is developed for educational purposes.