Machine countersinking the six holes in the F-1205B-L&R roll bar mounting plates that require flush pop rivets using a 120 degree countersink bit.
The F-1205B-L&R roll bar mounting plates also receive two nut plates each, so those rivet holes also required countersinking with a #40 100 degree countersink bit because the roll bar bases will be sitting on top of them. Prior to riveting the nutplates, make sure the AN4 bolts can go through the hole … after primer and paint I needed to run a 1/4" reamer through the holes to clean them so an AN4 bolt could be screwed into the nutplate to keep the hole centered while the nutplate is riveted.
Using a pneumatic rivet squeezer to install nutplates onto the F-1205B roll bar mounting plate.
The F-1205A mid fuselage brace is the next item that gets installed onto the fuselage assembly. The F-1205A mid fuselage brace is riveted onto the aft side of the F-1204B-L&R bulkhead sides.
Riveting the F-1205A mid fuselage brace onto the F-1204B-L bulkhead side.
After the mid fuselage brace is riveted in position, the F-1205B-L&R mounting plates and F-1205C mid fuselage brace closeout were secured in position with Clecos and now ready to rivet during the next work session in the shop.
Securing the F-1205B-L roll bar mounting plate onto the F-1205A mid fuselage brace with Clecos.
Placing the F-1205C mid fuselage brace closeout in position onto the F-1205A mid fuselage brace to secure with Clecos.
Return from the future ... RV-12 builders take note: The avionics kit contains the F-1205G ELT antenna mounting plate which needs to be attached onto the right side of the mid fuselage brace. The instructions in section 23-3 step 4 made no mention of leaving these three rivet holes in the mid fuselage brace open for the later instillation of the F-1205G ELT antenna mounting plate. As such, in my case, the LP-4-3 rivets need to be drilled out. Builders do yourself a favor ... when following the steps in section 23 for riveting the mid fuselage brace DO NOT place rivets into the three rivet holes on the mid fuselage brace shown in the photo below adjacent to the holes in the F-1205G ELT mounting plate being held in my hand.
DO NOT rivet the three rivet holes in the mid fuselage brace adjacent to the holes in the F-1205G ELT antenna mounting plate in my hand. To avoid drilling out rivets later these rivet holes need to be left open when completing section 23. These three rivet holes will become the mounting holes for the ELT antenna mounting plate shipped with the avionics kit.