Preparing for Deburring Dimpling and Countersinking of the Left Wing Leading Edge

I finally did some more work on the plane yesterday and today. Yesterday I put the LE back in the cradle after drilling all remaining rivet holes for the patch plate, subskin, and outer skin. I disassembled the first two inboard ribs so that I could separate the subskin from the assembly to debur both sides of the new holes. There were also a couple of scratch marks on the rear rib flange of each rib that needed to be scuffed out and re-primed. I re-shot them with some NAPA 7220 self etching primer (rattle can).

I then started reviewing Vans instruction manual - something I had not done in detail for a very, very long time. I had been so busy doing all the "other" things I needed to do for this modification that I am doing that there was no need to get back to the instructions in the manual until the large majority of things pertaining to the mod were completed.

The manual basically has you completing the LE structure, leaving it clecoed to the Wing spar, and then you start to work on the fuel tanks.You are supposed to get to a point where the fuel tank is mounted on the wing with the LE, and then you final drill the screw holes for the joiner plate where the fuel tank and the LE join together. It then seems to have you removing the LE from the wing and final drilling the rivet holes and riveting the nut plates to the joiner plate BEFORE you rivet the entire LE together. Right now I am not too certain how I am going to approach this.

2 years ago I had started assembling the left wing fuel tank after prepping, straightening, and fluting the tank ribs. It has remained in that state ever since. every time I put it on the wing next to the LE the parts marry up pretty nicely to each other, but the manual has you attaching the Fuel tank to the wing spar first, which means that the fuel tank mounting screw holes have been drilled and dimpled for the #8 screws that attach it to the wing spar. Basically this means that the fuel tank is completed first, and THEN you finish the LE.

I also recall that the instructions to mount and drill all the holes for the fuel tank have been deemed by most builders to be worthless, and much better methods have since been devised. I was following a web site that had this method all documented adn photographed, and now I need to find that site again.

After the deburring was done, I decided to countersink the rivet holes that attach the nut plates to the subskin for the new access panel. I decided to countersink the nut plate holes for NAS 1097 (oops) rivets, since they have a smaller flush head. but still accomplish the same job. Many builders do this for non-structural parts such as access panels or floor panels. The following pics show how I set up for this and tools I used.

I used my standard single-cutter deburring bit and my craftsman cordless screw driver to countersink the rivet holes. This next close up shows t he countersunk rivet holes and difference between the head sizes of the 1097 AN 3-4 rivet and the AN426AN3-4 rivet:

I used the deburring bit in the screw driver with the part clamped over the top of two pieces of wood with a gap in the middle so that could trial fit the rivet and remove it as needed until the countersink was set to the proper size for the rivet head to sit flush with the surface of the subskin.

Having not done this sort of work for a long time, I only over-did one of the rivet holes, so I had to keep going to size it for the regular AN426 AN3-4 rivet and I think that worked out fine.

This last pic is of the clamped part on the workbench. I am trying to make sure that I stick some very hard-learned lessons that securing the part properly is the most important thing to do when prepping a part for drilling, shaping, or riveting:

Next steps are to get out the C-frame and prepare to dimple the #8 screw holes. As memory serves, I believe it is always better to use the C-frame to dimple the larger holes, and very important to make sure they are  properly deburred and have clean edges, to prevent cracks from forming in these areas.SO this means I will have to get out my C-frame table - also something that I have not done in  very very long time, and setup my C-frame for these holes and the other holes from the outer skin. I used my edge deburring tool to smooth out the larger holes for the screws.

I also got out my pneumatic squeezer, my dimple dies, including my close quarter dimple dies, and my microstop countersink and corresponding bits, and started to plan out the dimpling and countersinking process for the LE.

All for now

KPR