It's Riveting

 

Replaced rivets along driver's side hemline.

This weekend I learned how to use a pneumatic rivet gun to drive solid rivets. These aren't the "blind" pop rivets most people are familiar with, these are solid metal, in this case aluminum. You use the rivet gun to pound the rivet against a "bucking bar" so that the back side smooshes out (the technical term) to hold the pieces you want riveted together. This only works if you (or a "bucker") can get behind the rivet with the bucking bar.

The entire shell of the trailer is made up of riveted 0.040" 2024T3 Alclad aluminum skin and interior Z extruded aluminum framing spars. There are a few places that they used some small 1/2" extruded aluminum L for stiffness, but it's really a simple fabrication approach with only a few different materials. Most trailers use wooden wall framing covered by aluminum skin.

The rivets heads can shear off under stress, and this trailer had quite a few that had sheared off along the bottom where the shell connects to the steel frame. I don't know if they were that way all along or it happened while I was dismantling the interior. Maybe a little of both.

In most cases when the head shears off it falls off, but there were several that I needed to drill out to remove. And the body of the rivet stays firmly lodged in the steel of the trailer frame. In order to install a new rivet you have to drill out the old rivet. Fortunately aluminum is fairly soft so the drilling wasn't too difficult. Typically I'd drill out about 1/2 the body and then use a punch and a hammer to pop out the body of the rivet. I initially tried a hammer and punch without drilling some of the body and that just didn't work.

Early Boles Aero trailers used 0.040" thick 2024T3 Alclad aluminum

I was curious about the specific material used in the trailer construction. It's important because I need to make some patches and at least one small repair to the skin. I'd read that Airstreams use 0.032 2024T3 Alclad so I assumed Boles did too. But while I was removing the interior I found a small vent cutout that had fallen into the wall cavity and measured it. It was 0.0395" +/- 0.001". I confirmed the type of material and also the thickness with a brochure I received from Marilyn Metz, who is the daughter of Don Boles the founder of Boles Aero.

My first practice rivet

I ordered a variety of rivet diameters and lengths from Aircraft Spruce and Specialty Co. They supply aircraft fabricators. The ones that they sent where anodized with a gold tint. The rivets on the trailer are a mix of plain aluminum color and gold anodized. The rivets come in different head shapes, the two used in trailers seem to be "universal" or "brazier", the latter is a bit wider. My Boles uses universal head rivets. The aluminum rivets also come in two basic type of material: hard or soft aluminum. You can tell which is used because the hard, or structural, aluminum rivets have a dimple in the center of the head. I've read that Airstreams use a soft brazier rivet. I'm sure there's some pro/con to each type.

The smooshed or "worked" side of my first rivet

Practice complete, on to the real thing

I used the small piece of aluminum I found in the trailer to create a practice piece. I drilled it and then proceeded to use the rivet gun to place some rivets. There's a trick to the drilling. If you're using a 5/32" diameter rivet you can't use a 5/32" drill bit. The rivet won't go in the hole. You need to use a drill bit that's slightly larger. In the case of 5/32" the size of choice is a #21 drill bit that's a few thousands larger in diameter. 

After practicing I started on the trailer. There is a lot of skill to placing a good rivet. I'm still learning. It's a good thing the rivets I placed are about 14" off the ground because no one will notice how badly I did. But I think they'll work and I did better with each one I placed. Hopefully when I get to the noticeable patches I'll have decent technique.

I ordered some sheet aluminum and "plain" (non-anodized) rivets to use for patching material, so we'll find out if my technique is acceptable in the next few weeks.