Marked parallel lines 10mm in from edge of doublers and measured off all the rivet hole locaations. Marked rivet lines for top bearing halves, rib #2, rib #3 and rib #4 so as not to drill doubler-attach holes in the vicinity of these component attachment locations. Clamped doublers to spar and match-drilled pilot holes up each side; except as noted above since they will require holes that do not fall exactly on the 40-pitch spacing. Finish drilled to #30 and deburred all holes.
4/11/10 lesson learned: Do not drill bottom holes in doublers. Instead insert the flange of bottom rib (#1) and mark a line for 5 rivet holes, the outer two being the lowest on the spar/doubler attachment. Make sure this line is at least 10mm from both the bottom of spar and top of the rib flange. Since pitch is the MAX distance between rivets it is important to first mark the end holes then space the holes in between according the the pitch specified; in this case <=40mm.
