I re-did the machine countersinking on the tab Z-spar to get a better fit with the dimples in the skin
When countersinking it really helps to have some back up material to keep the countersink centered. I’ve noticed that in the thin material when the bottom of the hole is penetrated with the countersink that it has a tendency to wander and give oblong holes. I used one half of the hinge with the matched holes for this.
