Abstract
Self-threading screws have some operational peculiarities. In spite of their economical advantage which require no prior tapping operation, one of the weaknesses of the self-threading screw tightening operation is that the screws could easily be tightened at a non-rectangular angle and thus resulting in improper tightening strength. The required criteria for evaluating such operation are identified. They are (1) Tightening torque, (2) Maximum vertical pressure and its timing of realization, (3) Driver tilt area at threading period and tightening period, and Driver tilt angle. In order to verify the criteria, an experiment was conducted taking work experience as a variable factor using 62 subjects with varying degrees of experience. As a result, the criteria were found to be effective and useful. It was revealed that the work experience had little effect on the performance which proved the effect of the peculiarity of the operation. By the use of the criteria, the workers with proper aptitude could be identified.
