4/16/2021 – 1.2 hours
Dimpling the aft bulkheads and tie down bracket is different for the tricycle gear and tail dragger models of the RV-14. I'm building the RV-14A (tricycle gear), so the description of this step is specific to the RV-14A. It is very important to identify the forward and aft sides of the bulkheads before dimpling to ensure the manufactured heads of the rivets are on the aft side of the assembly. It is also important to mark the holes that do not get dimpled. I noticed on another builder website that there are two holes in the bulkhead webs that are identified to dimple, but should not be. These two holes are just to the outside of the tie down bracket. The edge of the tie down bracket goes right through the middle of the holes meaning they will not get rivets and if they are dimpled the tie down bracket won't sit flush with the bulkhead. I marked the holes with tape and then put large *'s on them with a Sharpie to make sure I didn't dimple them.
The flanges of the forward side of the bulkhead (F-01412A) also have two sets of nutplate holes on each side that can “optionally” be dimpled for flush screw installation of the access panel that will eventually go there. The #40 holes to attach the nutplates get dimpled to fit beneath the side skins, and I opted to dimple the #27 holes for the flush screws as well. The aft side of the bulkhead (F-01412B) also has a set of nutplate holes at the top of each flange. Those nutplates are not used for access panels (they are above and aft of the access panels), and those #27 holes should not be dimpled. The #40 holes to attach the nutplates, though, should be dimpled. It is definitely worth some time to make sure the correct holes are marked to not dimple and to look ahead in the plans if opting for the flush screws in the access panels.
I made most of the dimples with the C-Frame, which I think does a better job than the pneumatic squeezer. The exception was the flanges of the aft bulkhead because they are canted inward slightly. The pneumatic squeezer was the best way to access those holes. The other operation in this section is to countersink four of the eight holes in the tie-down bracket that correspond to the dimpled holes in the aft bulkhead. I found that 0.007” beyond flush worked well for the dimple to nest securely in the countersunk holes.
[22” C-Frame and Hammer, Pneumatic Squeezer, 3/32” Dimple Die, 1/8” Dimple Die, #6 Screw Dimple Die, #30 Countersink Cutter]