Machine Countersinking Of Longerons Completed

Because of the flush rivets being utilized on the DOG Aviation RV-12 project, an additional step is required that is normally not necessary on the typical RV-12 … the recently drilled side skin holes in the longerons will require machine countersinking. Now that the F-1270 side skins have been removed decided it would be much easier to just machine countersink the longerons while they were on the fuselage. In an effort to eliminate shrapnel from the countersinking process getting all over the fuselage, a piece of Van’s packing paper was taped under the longeron to deflect the metal onto the shop floor and not inside the fuselage. Decided to start with the right longeron first so the shop would be warmer by the time I got around to starting the left longeron which requires needing to standing by the roll up doors which leak a tremendous amount of cold air.

Beginning the machine countersinking of the right F-1255 longeron. Paper prevents metal flakes from getting in the fuselage.

The countersink bit was set for the depth of the dimples the Cleaveland 120 degree dimple dies create in the side skin material. The countersink cage was adjusted so the depth of the countersinks would allow a dimpled test strip to set flat on the longeron. This ends up being about a click or two deeper than a CS4-4 rivet would normally require being flush. The air to the drill was adjusted WAY down so the countersink bit spun slowly and Boelube was used on the tip of the countersink bit for every hole.  One minor issue came up when attempting to countersink the rivet holes in the area of the F-1234 canopy base … the overhang of the canopy base interfered with the countersink cage preventing it from sitting flat on the longeron, so the canopy bases required being removed from the longerons.

The 120 degree machine countersinking of the right F-1255 longeron's rivet holes almost completed.

As with the right longeron, the shrapnel shield was used and the F-1234-L canopy base was removed so the countersink cage could sit flat on the left longeron.

Beginning the machine countersinking of the F-1255-L longeron.

Almost finished with machine countersinking the rivet holes on the F-1255-L longeron using the countersink cage outfitted with a 120 degree cutting bit.

Now that both longerons have been machine countersunk for flush rivets, the inside edges of all those drilled holes need to be deburred … so that will be first thing on the to do list during the next work session.