Wrestled the Tank back together and countersunk the skin-to-baffle holes

Last night I was able to get the tank clecoed back together. It took a while, but seemed to go together fairly well. After I got the rear baffled re-installed, I did a trial fit with my microstop countersink tool and noticed that it was a bit difficult to get the pilot of the bit into the rivet holes. After pondering that for a day I decided to run a #40 reamer through each of the rivet holes to ensure that the pilot of the countersink cutter could be easily inserted into the hole.

Vans instructs you to countersink the skin in this area so that you don't have to deal with proseal and dimples later on. This could make it difficult to fit the rear baffle onto the tank and ensure that it is properly sealed up. If you countersink the skin holes then the holes in the baffle plate can remain as is, with no dimples. THis makes it easier to slide the baffle plate into position and rivet it in place when the time comes.

Tonight, after I ran the reamer through all those rivet holes, I took a piece of .032 scrap and .025 scrap and clamped them together. Then  drilled #40 holes, deburred them, and then took the MS countersinl bit and did a test to ensure that the rivets would be set to the proper depth. In a phone conversation with Vans today they told me to set the depth so that these rivets would sit flush with the surface of the skin. I asked about this because  was not sure if I needed to countersink them a bit deeper to allow for proseal that might fill the rivet holes. They said to keep them flush with the skin surface because these rivets should NOT be exposed to proseal.

So I verified that the test resulted in the rivets sitting flush with the tank skin. Then the fun began. The fuel was in the cradle, and the cradle was clamped to my work table. I then started to countersink ALL of those rivet holes. I spot checked the depth every so often with an AN426AD3 rivet, and they all looked like they were going to sit nice and flush.

This also took a while, and by the time I was finished with both sides, it was pretty flippin' cold in the garage. Too cold for pics in fact. SO I called it a night. Next step is to cut and fabricate the stiffeners, cleco those to the tank and match drill the rivet holes.

During my call to Vans I asked all of the questions I mentioned in a previous post. Here are the answers:

1. Countersink all the skin-to-baffle rivets so they are flush with the tank skin.
2. Do create a void in the T-405 tank attach bracket to ensure that there is enough room to clear the few rivets that will be protruding    through the rib flange after the tank skin is riveted to the inboard tank rib.
3. Totally OK to leave the T-712 Z bracket flange UNPRIMED where it will be riveted to the rear baffle plate, and put proseal on the entire flange. Also need to leave the area o the baffle plate where that flange will be placed unprimed as well.
4. Perfectly OK to scuff out any scratches in the inside of the tank and leave them unprimed. When I asked if there was a concern about corrosion in the tank since I would be removing the alclad layer, I was told that the tank will have fuel in it most of the time, and it will be sealed except for the vent line, so corrosion from exposure to the air and moisture is not much of a concern for the inside of the fuel tank.
5. It is OK to scuff an area of the tank skin that is somewhat larger than the width of the rib flanges. Proseal will only be placed in an area relatively close to the rib flanges, bt for the same reason as described previously, scuffing and cleaning an area on the surface of the skin that is a bit wider is just fine.
6. Countersinking the .032 tank skin might result in "just touching" the metal of the baffle plate as well per Vans. Normally you do not think about countersinking something unless it is .040 inches thick or greater, but in this case you are instructed to do it by Vans for reasons previously stated. However, this means that almost the entire thickness of the .032 tank skin will be countersunk, and perhaps a small amount of the baffle flange that sits behind it. I will be curious to see how that worked out when I remove the baffle plate again to fit the stiffeners in place.

So I will scuff out the deeper scratches and don't need to worry about leaving the surface exposed after removing the alclad layer. That makes me feel a bit better. I have already been scuffing the inner surfaces of all my skins in a very similar manner anyway, so this will be like a normal routine for me anyway.

I also decided to remove the jacobs chuck in my older air drill and attach the quick change chuck, so that I could try it out and see how well that works. I did not want to remove the standard chuck in my Sioux air drill because I was concerned about not being able to use any drill bit sizes that did not have a matching quick change collet for them. However, that is when I learned that one of the attachments I received with the quick change set was an extension collet that has another 1/4-28 threaded shaft on the end, so that you can put that collet in the quick change chuck and then attach the standard jacobs chuck to the end of that collet, so you can still use any size drill bit by using this adapter. Even so, I still wanted to leave the original chuck in my sioux drill for now. I'll add more pics of all that tool stuff tomorrow.

KPR