What Are Rivets For, Anyway?

As America's Arsenal for Democracy shifted its Nazi-ass-kicking apparatus into high gear during WWII, the rivet reigned supreme as the fastener of choice for heavy manufacturing. Everything from buildings and bridges to planes, tanks, and automobiles were stuck together with rivets, fastened into place by air gun-wielding factory workers.

But by the time I was born in the late '70s, burly men and women pounding rivets into cars and trucks had more or less given way to robot arc welders gliding up and down sparsely populated assembly lines. Whenever I've seen a new building going up, I've seen people welding and guys installing high strength bolts, but no riveters. So both the significance of rivets and how they work has escaped me the three-plus decades I've been alive.

But rivets are outstanding heavy duty fasteners, and here's why.

Let's say you want to bolt a bracket to a steel beam. The bracket is going to hold a lot of weight and will be subject to jarring motion, like say, the spring mount on a truck frame would. So why wouldn't you just use a bolt to keep it in place? Simple. Sometimes, bolts don't completely fill the hole they're stuck through, so there's room for movement. They work, but there's still room for error.

Rivets are a different story. A rivet is merely a thin metal rod with one end deformed into a, uh, well, for lack of a better term, into a mushroom tip. The straight end is pushed through the hole drilled into the two pieces being fastened together. Then, with the deformed end of the rivet held in place by something big, heavy, and unmovable – what's called a dolly or bucking bar – the straight end of the rivet is struck repeatedly or squeezed until it forms into a mushroom tip, too.

Now, the two deformed ends of the rivet – which was once just a plain 'ol steel rod – pinch together the two pieces being fastened. But there's more to it, and this is the part I never realized. When the rivet is pounded/squeezed into itself, the whole rivet deforms, filling every nook and cranny in the hole in a way a bolt never could. That's why those suckers are so tight. Plus, you can choose the shape of the rivet's head by using different shaped dollies.

(It's poignant to mention here that their tightness, which usually can't be measured as well as a precisely-torqued bolt, can lead to failure during seismic events. That's why they're no longer used as structural fasteners in big buildings. Bolts are also easier for relatively unskilled laborers to install.)

Of course, small rivets can be placed and deformed cold, but the bigger rivets get, the more force it takes to deform them. It takes a lot of heat and pressure to form a big rivet, so it have to be heated up and squeezed into place by a huge pneumatic ram attached to a massive cast steel C-clamp jig. Smaller rivets, like those pop rivets you may have used or seen used on leather, canvas, or very thin sheet metal, can be placed with specialized hand tools.

Welded joints are stronger and lighter than riveted ones because you don't have to drill a bunch of holes in structural members and weight them down with myriad little globs of extra metal (rivets). Nearly all automotive frames are welded now, although not that long ago, crossmembers and spring hangers were mounted to frame rails with hot rivets. Sometimes, even engine components such as axle ring gears were riveted into place – not so great when the time came to replace the gear. Removing rivets is a messy job that requires drilling or cutting.

At a tech session hosted by the Early Ford V8 Club of Virginia this month, I learned that if you want to refinish an old car the right way, rivets are the only way to go on many structural parts. Much like the English wheel is losing practitioners, there are fewer and fewer people with the equipment and savvy to do big riveting jobs -- for the most part, it's a skill relegated to the aluminum parts handled by the aircraft industry. But from what the Ford guys said, you can fashion some of your own tools for riveting. Just keep in mind that the bigger the rivet, the more time-consuming the setup will be.

But if you have the time and the inclination to learn how to set rivets, there are worse ways you could spend your time.

Photo credit: Wikipedia

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