Using a spring-loaded center punch to dimple each drill hole location will center the drill bit and prevent it from wandering when starting each hole. However, trying to precisely eyeball the punch over the center of a drawn hole location is not an accurate process. To add repeatable accuracy I created a locator tool from a scrap piece of aluminum with a straight edge on which I added a small notch. Placing the edge over the rivet line and notch over a dot I was able to precisely center dimples very quickly.
Drilling was started at center of leading edge working in each direction while clecoing every other hole. Rib holes started at leading edge and progressed aft. The only holes that were not dimpled or drilled were the last holes on each rib at the trailing edge; these will be drilled on each side - independently - after skin is opened up.
