The geometric visualization skills and 3D modeling accuracy of vocational high school (SMK) students in Computer Aided Design (CAD) instruction were previously relatively low, as evidenced by difficulty in understanding relationships between geometric profiles, visualizing shape changes, and producing accurate three-dimensional models. This study aimed to improve students' geometric visualization skills and 3D modeling accuracy through reverse engineering-based CAD instruction utilizing the Loft feature. The method employed was Classroom Action Research (CAR), conducted in two cycles—each comprising planning, implementation, observation, and reflection—involving tenth-grade SMK students enrolled in a CAD course. Data were collected through observation, questionnaires, and practical tests. In the pre-cycle stage, instruction without reverse engineering resulted in an average score of
86.33 with a mastery rate of 77.78%. Cycle I increased the average score to 88.74 (mastery rate 86.42%), while Cycle II, using more complex objects and intensive guidance, raised it to
91.47 (mastery rate 93.83%). Observation and questionnaire results also showed improved student precision in geometric and three-dimensional modeling. This study concluded that reverse engineering-based CAD instruction using the Loft feature effectively improved SMK students' geometric visualization and modeling accuracy.
