Trap Door Fabrication, Continued

Picking up from my previous post, the hinges, door, and spacer are fabricated. Now it is time to position everything on the rib and drill the necessary rivet holes.
Here some pics showing how I drilled the upper hinge rivet holes:

And here are the holes in the lower hinge:

And this is where is starts to get more challenging. The next step is to countersink the right holes in the right part. It goes something like this:
- The lower hinge is only attached to the upper hinge via the hinge pin, and to the actual trap door.
- The trap door holes get dimpled, and the back side of the lower hinge holes get countersunk.
- The upper hinge is attached to the spacer and then finally to the rib web. SO in this case the top side of the upper hinge is countersunk, and the rivet then goes through the holes in the spacer and the rib web.

So you have to make sure that you countersink the right holes on the correct side of each hinge. If you screw that up, you get to start over. Perhaps this is not an issue for other folks, but for me it was a bit unnerving. Hinges are a bit strange for me to work with, because they are made from a different alloy, with a different hardness, and a different thickness than other types of alclad aluminum.Their dimension and general shape also make them a challenge to work with.

One of those challenges is that I find it difficult to try to setup the work so that you can use a microstop countersink tool to drill the holes - mostly because the holes are typically very close to multiple edges of the hinge, an the part is small, so the tool does not sit well. The shape of the hinges also makes it difficult to butt up multiple hinge halves to give the tool more surface area to sit on, as I have done in other situations when working with flat aluminum alclad.

So, I resolved to countersink the less elegant and more error-prone way, by using my deburring bit in my cordless drill, and carefully countersinking each hole and trial fitting it with a rivet to ensure that I don't go too deep. Here I am burrowing out the holes in the back side of the lower hinge that will accept the dimples from the trap door.

And a test fit with a rivet. Not the best job, but its good enough for me:

Its OK if these are a little deeper than flush, because they will need to accept the dimples from the trap door. Next came the fitting and drilling of the holes from the upper hinge half in the spacer and the rib web. I found this to be the most challenging part of this little project. Had to get downright inventive about how to clamp that sucker down and position it exactly where it needed to go to ensure that door ends up in the right position. I found a small clamp or two that seemed to work out well enough - as able to insert it through the fuel feed hole in the rib - you know - the hole this door is trying to keep covered some of of the time:

After using the hinge to match drill holes in the rib web, I then needed to match drill the same holes through the spacer. I drilled the first hole through the rib web to the spacer, and then I needed to re-position the clamp to the corner of the spacer in order to hold it in position well enough to drill the other hole.

once the upper hinge and spacer were drilled to the rib web, next came the lower hinge and the trap door as shown  here.  decided to mark the hole locations in the door so I could remove the assembly from the rib, since none of these holes are going to go through the rib. I did not want to risk accidentally drilling into the rib web, so I marked the holes on the door with a sharpee so I could realign them again after removing the hinge and the door from the assembly

I put a piece of tape over both parts before removing them from the rib to help keep them aligned with each other.

Next was another trial fit after the holes were all match drilled and countersunk, etc.

And then finally is a shot of the two upper holes and where they ended up in the rib web. You can see from this pic just how close to the edge of the stiffening ring it is. This shot also demonstrates the question one has concerning how Vans seems to think that you can make three rivet holes in this area instead of the two that you see. The stiffening ring/depression makes this virtually impossible.

On that note - just one more thought about this whole situation with the fuel tank and this whole trap door fabrication business. One of things that I have become very aware of as I have continue to work the fuel tanks is the need to ensure that anything that is attached in a certain or is added to the tank assembly MUST NOT fall apart, break off, or become loose and fall off while inside the tank. In one case you might experience odd behavior with the fuel system, and in the worst case you may experience a blockage in your fuel pickup line that will cause fuel starvation at some point in the system. As such, all of the parts involved in this trap door fabrication are a concern for me, as well all the parts that make up the entire flop tube assembly.

Everything from the hinge pin to the rivets to the parts is a concern, and whatever you decide to do, you have to end up feeling confident that the added pieces and parts you are putting in the fuel tank are not going to cause a bad situation in the future. You need to k now that the extra rivets are not going to break or come loose, and the clunk on the end of the flop tube will not loosen from the tube, and so on. During my research I have read many accounts of folks that have ended up with a variety of issues with the fuel tank components from time to time. And at the same time I have also ready about folks that have had trouble-free tanks for years. I guess it all boils down to paying attention to details and being very safety-minded when working on the tanks.

This trap door assembly, fuel sending unit, and the flop tube are the only three moving parts that I am will to accept inside the fuel tank. Those 3 components provide numerous "opportunities" for things to fall apart or cause other problems. Add to this the blatant fear that most folks feel about sealing up their tanks properly, and this whole part of the project can become quite stressful. That's why a lot of builders opt to have their tanks built by someone more knowledgable and experienced. As for me, I am a builder, and the only way I will become experienced is to just dive in and do it, and seek expertise from those that are the experts.

Next up will be riveting this trap door contraption to the rib, and putting the final bend on the other side of the hinge pin.

KPR