Ivan's RV-7

Riveting firewall togetherTimer icon4h

September 1, 2022

The last step was to rivet firewall parts together.

Today I riveted the firewall together. However, before that, I received "mock" batteries from EarthX: "C" case and "E" case. They are just plastic boxes that could be used for fitting batteries.

I ordered them to figure out the future work to install batteries. The was a report on VAF saying that you will have to redo some work and also will need to resort to counter-sinking (instead of dimpling) when installing some of the parts in the future. After researching what kind of work will be done in the future, I concluded that I don't need to plan for it. Too many unknowns.

In some cases, it would be removing some rivets and upsizing the hole for the bolt. In other cases, I will need to countersink to install nut plates, but since I use NAS1097 rivets for nut plates, I will countersink either way. In both cases, it seems okay to redo some work.

So I decided to install every single rivet and then modify it as necessary in the future.

However, I like the size of the "C" case: it is very compact. Since I plan to install two batteries, any space I can save is good.

Mock EarthX batteries.

Then I proceeded to rivet the parts together. I squeezed all perimeter rivets which I could access with the manual squeezer. After that, I back riveted everything else.

The hardest rivets were the ones that attach F-601J angles to the F-601N stiffeners: there was very little space so my back riveting set did not fit. In the end, I bucked them the normal way, with the flat set and the bucking bar. They came out ugly, but acceptable. A few of them are on the smaller size (the pressure was a bit too low so I hardened them a bit instead of swelling), but still larger than the minimum 0.163".

One rivet I drilled two times before I got an acceptable result. So I ran out of AN426AD4-9 rivets in the end (there were only a few spare ones).

Interestingly, the plans use both AN426AD4-8 and AN426AD4-9 for attaching these angles even though the thickness is the same everywhere (and yes, even though AN426AD4-8 give acceptable result, they are on the smaller side).

Tight rivets on an angle.

The completed firewall bulkhead.

Firewall riveted together.

The view from the back.

View from the back.

Finally, I drilled two holes that are used later to attach a motor mount. I drilled the holes with a #40 drill bit first, for which I used a drilling bushing I made before. It worked fine for the first hole, but the second hole came out extremely crooked. I think, the drill bit grabbed while drilling: the hole goes exactly between two parts under the mount so there is a narrow gap between them.

Hole did not go as planned!

Luckily, I used a #40 drill bit, so I was able to use a small file to straighten the hole and upsize it to a #14 drill bit, then use a #12 reamer to clean it. The plans call for a 3/16" size, but the #12 reamer is close enough (0.189" versus 0.1875").

Hole straightened and reamed.

The very last thing I did was I filed two holes in the recess that did not match with the firewall holes to make it possible to insert a rivet through them. The holes are definitely oversized now, but since the recess is stainless which is much stronger than aluminum, I think, it is okay. The underlying firewall sheet and the stiffeners have correctly sized holes.

Hole filed to fit.