Effect of various aircraft production drilling procedures on hole quality

A two part study was conducted on the effects of hole drilling on the fatigue life of aircraft rivet holes in 2024-T3 aircraft quality aluminum. In part one, a study was conducted on the hole quality effects of the drilling in order to reduce the number of variables in the fatigue study. Six production-line factor variables are considered: the experience of the operator, the use of a pilot hole, the length of the bit, the condition of the bit, the axial pressure or feed rate, and the rotational speed of the bit upon withdrawal from the hole. Four metrics were measured to define hole quality: surface roughness, hole ‘conicality’, the number of large gouge marks, and the angle of those marks. The pilot hole was found to produce the greatest overall effect on hole quality, improving hole quality with its use.