Breaking down the RV-12’s roll bar assembly for deburring and machine countersinking. Note the tags placed on the bottom aft holes of the F-1231B&C straps to insure correct orientation during reassembly.
Deburring the F-1231B roll bar strap with the hand deburring tool.
Deburring an inside rivet hole on a F-1231A roll bar frame by manually
turning the shaft of an angle drill attachment outfitted with a deburring bit.
Holes on the outer flanges of all four F-1231A roll bar frames receive machine countersinking because they will lie under the rear window or canopy. The countersink cage outfitted with a #30-120 degree countersink bit was used to countersink all of the rivet holes on the outer flanges of the four F-1231A roll bar frames to accommodate flush 4-4 pop rivets … with one exception. The rivet holes at the base of each frame that are common to the roll bar mounting are NOT machine countersunk.
Machine countersinking the outer flanges on one of the F-2131A roll bar frames
using a countersink cage outfitted with a #30-120 degree countersink bit.
One thing I've noticed about the flush 4-4 pop rivets Van’s supplies with the RV-12 kit is the heads are slightly smaller than the Gesipa 4-3 pop rivets being used on the project. I knew this, but forgot to back off the countersink cage a few clicks … so the first hole countersunk ended up being a little deeper then optimum ... oh well, at least I noticed. Also suggest builders stop the countersinking prematurely in the areas where the curves are on the F-1231A frames and check the countersink depth. Because of the curvature of the frames, the countersink depth can easily end up deeper than those on the flat areas … so adjust your technique accordingly.