RV-12 Roll Bar Machine Countersinking

Following the drilling of all the #40 holes in the RV-12’s roll bar assembly to #30, the roll bar assembly was dismantled for deburring. After drilling, care must be taken to make sure the correct orientation of the F-1231B&C straps is maintained. Small loops of wire and name tags were placed in the lower aft most holes and the plans marked accordingly so during assembly later down the road after primer and paint, the parts will fit correctly. The outer holes of the F-1231A roll bar frames were easy deburred, but the standard deburring tool did not have enough clearance for proper deburring of the inside holes. For the inside holes, the angle drill attachment came in handy once again … the deburring bit was removed from the deburring tool and screwed onto the end of the angle drill. The shaft of the angle drill was then turned by hand to rotate the deburring bit a turn or two to remove the burrs. Worked quite well. A word of caution … don’t even consider attaching the angle drill attachment to a drill gun, it will spin the bit way too fast and quickly cut into the rivet hole far too deep.

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.