Obviously I Have Not Rivited Anything in a While

Today was rivet day for the three inboard tank attach nut plates before I start riveting the ribs in place on the main wing spar. I thought this would be a good way to practice setting some rivets after a long dry spell, and I was right - it was good "practice," but unfortunately the practice did not make "perfect."

It all started as usually does - with a lot of research and planning. I spent time reviewing Dan Checkoways info when he did both of his wings. I thought I had all the info I needed by reviewing his right wing posts, but I found additional very useful information in his left wing posts which came later.

The reason why it is good to go ahead and set the nut plates for this inbard tank bracket is that you can use them to secure the inboard Z bracket instead of a nut and bolt combination which he used to help properly position all of the Z brackets for the fuel tanks. I'll get more into all that in the months to come, but for now I will simply say that I will use Dan's method to properly position the Z brackets since Vans instructions for this definitely do suck.

The other reason you set these nut plates now is that it is easier to get to them without the ribs getting in the way. The holes for the nut plates are predrilled and just a bit undersized as usual. To drill them to the final size for the nut plate rivets as well as for the bolts, you use a #13 and #40 drill bit, and a #12 reamer. I ran the number 13 drill bit and the #12 reamer through the bolt holes, then I attached the nut plates with clecos drill those with the number 40 drill bit. I checked the fit for the bolts and they were spot on perfect.

Here are the first set of tools used. I have the drill bit and the reamer in two separate drills to make the process go a bit faster:

Next are the nutplates clecoed into position with one cleco. This is the way that they are positioned. Pay attention to the ones on the top and the bottom that are angled to account for the edges of the lightening hole cut out of the doubler plate of the wing spar. These presented several challenges.

I added another 2x4 piece of wood to the spar flange at the root and secured with a large C clamp to provide some additional resistance and rigidity to the wing spar which is critical during riveting. Before it is all said and done I will be using some beefy 4x4s and more clamps when I start riveting the ribs in place:

And here is shot of my work bench after leveling the front edge of both of them and placing two drill boards on top. I am finding that the bar clamps do tend to get in the way and if I am not careful I will snag one and maybe rip the hole spar onto the floor. C clamps and blocks of wood would probably work better for this, but I will stick with what I have for now:

A few more preparation items were to apply painters and masking tape to the spar bars and spar doubler areas. Turns out I probably should have used duct tape but I was afraid I might not be able to remove it very easily so I opted for something else. That may have been a mistake.

I also needed to run a test for my #40 countersink to make sure it is set to the correct depth. I already had the bit in one of countersinks but was not sure of the depth was correct. Turns out it was a good thing I ran some tests because for whatever the reason it was set way too deep. That could've potentially ruined the entire wing spar.

Here is the setup for the tests using my scrap 1/8 inch thick piece of aluminum from my empennage trim bundle:

And here are the three test holes. The one on the top was the original setting - note the rivet head sitting way to far down in the countersink. The other two were spot-on perfect:

Here are some of the tools for countersinking the rivet holes and the tape I used to protect various parts of the wing spar:

Now for the countersinking experience. As with most things about this build - some things are easy, and some things are less easy. I was able to use the Microstop countersink tool for all the rivet holes except for one - the one closest to the top side spar bar. the diameter of the cage was too big for the pilot to be able to fit inside the #40 drilled hole on the top side.I thought this was strange since I was able to use it on the bottom-most hole with no problem. So this meant that the rivet holes must be closer to the top spar bar than the bottom spar bar. Anyway,I had to figure out how to countersink that last rivet hole. I ended up doing it by hand using the debur bit and the countersink bit. I had to be careful to make the countersink as symetrical as possible, and it turned out pretty good.

After all the countersinks were done, I sprayed a cotton swap with 7220 primer and used that to prime all the bolt and rivet holes. When the primer was dry after a couple of minutes I taped up my flat rivet set that I have been using in the rivet gun, and used the thin man bucking bar to buck all the rivets for the nut plates. Here are the manufactured heads - some sitting slightly proud, but otherwise not too bad. There was no real issue with the flat set hitting up against the spar bars a little - the tape seems to have prevented any dings here:

And now for the problem side - the shop heads on the nut plates. It went something like this:
1.The first rivet was the top most rivet - I over drove it but otherwise it went well - or so I thought until I removed the tape to find a small ding in the double plate where my rectangular bucking bar contacted the edge of the doubler plate - dammit!

2. I did the same thing again on the lowest rivet - something about trying to fit a square peg into a round hole comes to mind. The problem is that you only have room to fit a small corner of the bucking bar onto the rivet shaft. Normally you try to center the mass of the bucking bar onto the rivet shaft so that it is balanced on both sides. This helps prevent slipping of the bar off the rivet shaft. If you move the bucking bar too far over to the side you run right smack into the spar doubler plate. Here is the pic:

With that pic you can see the nice ding on the lower left side of the doubler plate. I had tape on that similar to what you see on the top side, but it obviously did not do any good.

3. What is not visible in this pic is the condition around the bottom rivet of middle nut plate. You know, the easy one that I left for last after figuring AI would tackle the harder rivets first - easy access to the rivets with bucking bar, no interference with the spar doubler, etc. Well,on that rivet, the bucking bar slipped down and contacted the spar web - left a small scratch that I now have to dress out. The worst part is that it also chewed up the bottom of the nut plate flange so I have to replace this entire nut plate, and probably will have to replace the other two after I drill out other poorly set rivets on those. Six lousy rivets and I managed to make more work for myself. I can file out the dings in the doubler plate so I am not worried about that - but I really hate the thought of having to replace those nut plates again which means having to be careful with the bucking bar all over again.

Bottom line is that these nut plates really SUCK! I'll deal with all this tomorrow, but I had hoped to be moving on to riveting some ribs - guess that will just have to wait.