Visualizing parts, meaning interpreting the views of an object which has been represented in a drawing, is a fundamental skill in engineering. However, learning deficiencies and difficulties have been observed among engineering undergraduates, and there is a high failure rate in drawing courses. In order to determine the origin of these deficiencies, a qualitative design has been developed based on personal interviews. A group of students was interviewed to analyse the solution process they applied to three visualization problems with increasing difficulty. The steps they took were structured and categorized along with the difficulties and deficiencies which were detected. Most of the students affirmed that they did not possess methodology to solve these problems and relied on trial and error and intuition. The results seem to indicate that there are specific difficulties and that it is possible to define a set of skills which guide students through the process of visualizing parts. (Contains 2 tables.)