Today, I continued working on the mounting "toes" for the firewall. First, I used my 3D printer to make some spacer blocks. This let me provide a consistent offset between the face of the fuel tank and the firewall.
Here they are on the floor of the car, just aft of where the driver's seat will go.
And here they are looking down between the firewall and the tank. This let me get the angle brackets I had made all drilled and riveted up, so the lower portion of the firewall is all ready to bolt into the car.
To get the upper part ready, however, I will need to change tactics. Here are two rivets - on the right is the "pop" type that I have been using for most of the panel attachments throughout the car. The disadvantage of this type of rivet is that it is not flush on either side of the joint; on one end, it leaves a small domed surface, and on the other end, it leaves a protrusion which is even larger.
On the left is a bucked style of rivet, which is set with a rivet squeezer; it actually deforms into countersunk a countersunk hole on the back of the work to provide a flush finish on both sides.
These are aircraft rivets, used in applications where drag reduction is paramount, so no protrusions can be allowed.
Here's my first experiment is using these bucked rivets. This is the back side of a joint I made in a couple of pieces of scrap. I took two pieces of 1/8" aluminum, drilled holes and made countersinks on both sides, and used a rivet gun to deform the "shop end" of the rivet to fill the countersink.
Safe to say these pieces are securely fastened. I did a few more just to do it, and they all worked very well. I'm convinced.
Last but not least, here's the upper section of the firewall. It's all Clecoed up to a piece of angle, ready for the rivets to go in. I haven't shown it, but the holes are already countersunk on both sides, and I just have to buck the rivets.
That's for next weekend, though.