Match drilling the F-1201H upper fuselage doubler into the F-1201J cowl hinge.
Match drilling the F-1201H upper fuselage doubler into the F-1201K cowl hinge.
Both F-1201J & F-1201K cowl hinges match drilled.
At this point the RV-12 plans instruct the builder to disassemble the parts for deburring and then machine countersink all the hinge rivet holes in the F-1201H upper fuselage doubler. I would suggest fellow builders NOT disassemble the parts just yet. Machine countersinking the #40 holes in the F-1201H creates a knife edge condition which easily allows the countersink bit to wander and enlarge the hole unless a backing strip is used to prevent the pilot tip on the countersink bit from wandering. The easiest solution is to use the freshly drilled thick hinge material as the backing strip and machine countersink the F-1201H’s rivet holes by removing one Cleco at a time and countersinking. Be sure to adjust the air pressure so the countersink bit spins slowly and drip Boelube or some form of lubricant onto the countersink bit’s pilot tip. The hinge material will prevent the countersink bit from wandering as the countersunk rivet hole in the F-1201H becomes knife edged … and the slow speed and lube prevents the hole in the hinge material from wearing. This worked great!
Machine countersinking the rivet holes in the F-1201H one at a time with the hinges Clecoed in place to keep the countersink bit centered. Nice countersinks were obtained by slow speeds on the countersink bit and lube.
After all the rivet holes in the F-1201H upper fuselage doubler were countersunk, the parts were disassembled and deburred then reassembled for riveting using AN426AD3-3.5 rivets.
Using the pneumatic squeezer to rivet the F-1201K cowl hinge onto the F-1201H upper forward fuselage doubler.
F-1201J and F-1201K cowl hinges riveted in place onto the F-1201H upper forward fuselage doubler.