Drilling holes in the new joiner plate

With the new joiner plate/subskin fabricated and bent into shape to match both 408 ribs, it was time to start the process all over again to drill the rivet holes. Per the post on VAF that I referenced a while back, I followed similar procedures for this, which basically involved marking the hole locations with the drill bit instead of trying to drill through several layers of metal for different parts all stacked together in a situation where they cannot be easily clamped in just the right spot to ensure that all holes are aligned through every part. Having already been through this agony several times with the original 408 ribs and joiner plate assembly, I sure as hell did not want to screw this up again, so I took my time.

The first set of holes to drill into the new joiner plate are the same set of holes I drilled before on the most inboard 408 rib. This is the part where 11/16th of an inch of the joiner plate must extend beyond the edge of the LE skin to provide a mounting point for the fuel tank skin and associated #8 nut plates and screw holes. The only difference is that the rib has already been drilled for the skin attach holes. So I only needed to locate the holes of the joiner plate through the LE skin, and ensure that the 11/16ths of an inch was properly positioned.

I placed the new joiner plate over both inboard 408 ribs and then measured the 11/16ths just as I had done before. I clecoed the LE skin to the main spar, and the rear flanges of all the ribs to the main wing spar web. I reached inside to make sure that the second 408 rib was as straight as I could possibly make it. THen I simply took a number 40 drill bit secured in my air drill without having it connected to the air line, and I inserted the bit through the predrilled LE skin holes and then spun the drill chuck manually several times to carve out just enough metal to leave a noticeable mark on the part. Once all the holes were marked this way I removed the clecos from the LE skin, removed it as well as the new joiner plate, and placed it on my drill board so I could final drill the holes:

After all of these holes for the inboard 408 rib were drilled, I had to reinstall everything again. THis time, with the inboard holes drilled through everything, I could cleco the inboard LE skin, joiner plate, and rib flange holes together. this served as a stable method to align and position the rest of the joiner plate so that the second set of holes could be marked and then final drilled, following the same procedure I used for the most inboard holes. I did not drill through the entire joiner plate - just marked the holes, disassembled the LE, and placed the joiner plate back on the drill board again, just as before. IN the pic below you can see the first set of holes on the left, and new marked holes on the right:

With all the rib flange holes drilled in the new part for both inboard ribs, I could now mark the center line of the rib flanges on the second 408 rib, cleco down the LE skin assembly one more time, and look through the holes in the skin AND the joiner plate to locate the center line of the rib flange as shown:

Remember that all of the pics in this blog can be clicked on to enlarge the photo and see more detail. I proceeded to drill all the holes through the skin, plate, and rib flanges, and after removing the LE assembly one more time verified that all the holes appear to be in a position on the rib flange that I consider to be acceptable, which is not too close to the bend radius and not too close to the outer edge of the flange. I'll have more pics of this later. This basically means that I now have a new sub-skin/joiner plate part with all the holes drilled in just the right place, even after replacing one of the original W709 ribs with another 408 rib to allow for the thickness of the wider joiner plate that I using for this LE modification. I am relatively pleased with the way this turned out, even though it added several days and hours to the build. I still need to repeat this process for the right wing, but now I know all the steps that I need to take,and all the fixtures I needed for forming the part have also already been created. Unfortunately, since I messed up the measurements on the first skin I have to order a new one, and that will take several days to receive from Vans, so it looks like I may be heading back to some fuel tank fitting and hole drilling in the near future.

Next steps are to debur the holes in the rib, and after a visit from my technical counselor John Linz, he suggested that I should go ahead and fabricate some rear rib flange extensions so that I can use both of the outer holes that were predrilled in the main wing spar for the W709 rib for the new 408 rib. This should be an easy thing to do by using some .032 scrap to create a small flange and attach it to the rib web with a correct amount of rivets per AC 43-13. That will solve the questions and concerns I had about the difference in the size of the rear flanges for the two different LE ribs. Once that is done I can proceed with marking and drilling the fuel tank attach screw hole locations on the new joiner plate, essentially picking up where I departed from the original plans.

As for the new joiner plate/sub-skin support - next steps for that are to carefully measure and mark where the flanges for all the additional nutplates will need to be located so I can trim the part to remove all the unnecessary excess. So still lots to do - just need to remember to measure about 30 times and cut/drill only once. I don't want to screw this up now or I get to start it from scratch all over again.