Continuing with Dimpling and CounterSinking holes for the LE

Starting with some pics from the dimpling of the LE outer skin mentioned in my previous post:

This was a bit of a chore that required me to clear away a large area of the work bench to be able to maneuver it so that each hole could be dimpled. This was complicated for me because my dimpling table is on the bench, the back side of which is right up against the wall. So this restricts my ability to position the parts and also to position myself so that I can hold and hit the ram with both hands to properly form each dimple. Since space is restricted I found that I have to get very creative about how I position myself to be able to set these dimples. Translated another way, it means that I have to bend my body in some very unnatural and uncomfortable ways to be able to do this.

SO I can tell you right now that I am not looking forward to dimpling the larger outer wing skins, and I may go ahead and try to set up a level method on the garage floor, away from the work benches, just so it will be easier to move both myself and the sink around on the dimpling table without risking throwing my back out of whack. Not fun.

The next 2 pics show my re-assembly of the LE after I got most of the skin dimpled, except for the several holes that I missed match drilling as I mentioned in my previous post. I started reassembling by clecoing the subskin to the outer skin first, just to try to align the dimples. then I decided to reattach the center ribs first, followed by the outer ribs and then finally the inner ribs. I had numbered each rib with a piece of tape to ensure that each rib was reassembled in its proper place. (Read on for a humerous blunder that I made regarding the rib position).

Some complications arose:
1. I discovered that I had not dimpled two of the forward most holes in the subskin - I just missed them after I finally decided to dimple all the holes. So I had to detach the subskin, dimple the holes, and reattach it again - more wasted time.
2. After the LE was completely reassembled, it was time to put it back on the wing spar so I could match drill the remaining skin holes to the wing spar that I missed, and to match drill the W-423 joiner plate holes for the nut plates between the fuel tank and the LE. The only problem was that when I tried to reattach the LE rear rib flanges to the main wing spar web, I would not get the clecoes inserted into the end-most holes in the #3 rib position.

I removed the LE several times trying to figure out what was wrong. the first time I thought it was excess primer in the holes, so I ran a #30 drill bit through each rib hole.Then I put it back on the wing spar, but still had the same problem. SO I took it off again. This time I noticed that one of the rear rib flanges had 2 extra holes in it, and I remembered that one of these ribs had rear flanges that were pre-drilled from the factory, but they must have been a different hole pattern for an RV-6 or RV-7. SO for the RV-8, they tell you to match drill 2 new holes in this rib and to disregard the other holes.

It was then that I realized that I must not have the right rib in the right location. And sure enough, when I checked the rivet hole pattern for each rib flange on the main wing spar, that was exactly the problem. The funny thing is that I think I messed this up clear back to when I primed each of the LE ribs. I remember picking them up from my priming table when I was all done, and I was all but certain that I had picked them up in the proper order. it just so happens that this number 3 rib has a slightly different rivet pattern that the rest of the ribs. SO once I switched the #3 and #4 ribs to the proper locations, everything magically fit back together again properly, but NOT before I had removed and replaced the LE assembly on and off the wing spar about 4 times. So that was last night's big blunder:

After resolving that problem, all the ribs seemed to fit nicely in the dimples with the skin. The next step was to set my microstop countersink tool to the proper depth by testing it on some scrap pieces. it is amazing that you can set this tool to provide a countersink that is accurate to 1/64th of an inch. I put a piece of angle between 2 drill boards and marked several holes that are far enough apart for the frame of the countersink tool. then drill drilled the holes and used a rivet to check the depth.

This procedure is also perplexing to me, because I am able to set the tool so that the rivet heads do sit perfectly flush in the holes. But the problem is that every time I actually set rivets in these hole to attach parts together, the rivets seem to end up slightly proud of the top part being riveted. This happened quite a bit when I did the holes for the fuel tank nut plates long ago.

So then yo are left with a decision to make - if you should counterskink just a little bit deeper or not so that the rivet truly does end up flush. The question then becomes, how much deeper do you countersink? SO I did some tests with a few different settings and decided which one I wanted to use, and proceeded with the holes in the wing spar flanges.

The other piece of metal in the top pic was a test piece that I made with one dimple in it to check the depth against the spar flange after the countersink holes was drilled. The test is to see if the dimple fits correctly in the countersunk hole so that the skin then sits flush with the spar. My past experience with this is that the parts tend to get slammed together pretty good with you actually  rivet them together, so if the trial fit with the test piece looks good then it should definitely be that way when everything actually gets riveted together.

With the depth set, I went ahead and countersunk all the spar flange holes for the LE skin. About 128 per side for the LE. I think they came out pretty good, and the real test was clecoing the LE in place again. The skin seems to butt flush against the spar flange along the entire span, so I am happy with the results.

I then match drilled the missing holes, which I will have to debur, dimple, and countersink when the LE comes off for what should be the final time.

The last thing I did was to secure the fuel tank assembly next to the LE, so that I could FINALLY match drill the joiner plate screw holes that secure the tank to the LE skin. I was a little surprised that after dimpling and securing the LE and then butting it up against the tank that the bottom side skin has a small gap, but the edges from the middle to the tip of each skin seem to match up just fine. The top side of the skin does not seem to have this gap. I was a little disappointed, because prior to dimpling the LE this joint was completely perfect, with no gap. I guess I will have to wait until I dimple the tank skin screw holes and get it ready for riveting until I will no for certain if there is still a gap there or not.

Here are the shots of the bottom and top side skins of the tank and the LE with everything tightly secured with clecoes. The holes for the screws for the fuel tank skins that attach it to the wing spar flanges are secured with #30 clecoes that go all the way through the #8 nut plates that were attached to the wing spar flanges a long time ago.

The last pic is of the end of the wing along the wing spar flange line, showing the flush fit between the LE skin and the wing spar flange. Although this pic only shows the very tip of the skin, I checked it along the entire span for both top and bottom skins, and the fit between the dimples in the skin and te countersunk holes in the spar flange seems to be good enough for me.

One last note: In order to countersink the LE attach holes in the wing spar flange, the bottom and top skins need to be removed, so that the countersink tool can rest on the spar flange properly. The bottom skins had been removed a long time ago, so that was not an issue. However, the top skins remained on to provide strength and stability to the frame. Since they needed to be dimpled anyway, I removed the top outer skin so that I could countersink the holes for the LE on that side. This was the first time I had removed the top skins in a very long time.

Next steps:
Measure and mark the cut lines and rivet/nutplate hole locations for the removable LE. Then drill #40, followed by #30 holes for the primary rivets and screw holes along the left and right edges and the top and bottom rear edges. This needs to be done with the LE secured in place.

Need to decide what to do with the Stall warning holes. IF these will be removed by cutting out the skin section that I plane to use for my removable skin, I need to do nothing. If they will remain, I need to prep them to close them up, as they will not be used for anything in my plane.

1. Match drill the joiner plate holes to #30 only. Need to be careful not to drill into the spar bars of the wing spar so a drill stop is a must have for this. You don't drill the #19 holes for the screws until AFTER you remove the assemblies from the wing spar, for the same reason.
2. Remove the LE assembly and dimple and countersink those few remaining holes after deburring them.
3. With the fuel tank and Z brackets secured to the spar, match drill the inboard fuel tank rib, baffle, and Z Bracket rivet holes.and cleco them in place. Use a long, 12 inch #30 drill bit with a drill stop securely attached to prevent drilling into the wing spar.
4. With the LE removed, you can also access the outer-most tank rib, baffle, and Z bracket holes to match drill those.and cleco them into place. Use the same drill bit as before.
5. Remove the fuel tank skin and inner ribs from the wing spar, leaving only the baffle plate and the inner and outer-most tank ribs. Then match drill the remaining inner tank rib Z bracket rivet holes through the rear baffle plate.
6. Place primer in all the countersunk holes in the wing spar flanges for the LE
7. Dimple the top outer wing skin
8. Countersink the remaining wing spar flange holes for the top outer wing skin.
9. Apply primer to those countersunk holes
10. Reattach the outer wing skin and check the fit against the spar flange.
11. Make the stiffeners for the fuel tank, match drill them and cleco to the tank skin
12. Match drill the fuel tank skin and rib holes. Disassemble and debur all holes
13. Final drill and dimple all nut plate and screw holes in the joiner plate.
14. Final drill and dimple the screw holes in the Fuel tank skins.(top and bottom)

And then I need to disassemble the LE subskin and ribs, and make the necessary cuts to the LE outer skin.

Then we go from there.