Bomber seats have been used in racing cars for many years. The term comes from the days when military surplus aircraft seats were fitted into competition cars to save weight. Now there is a trend for many traditional-style cars to use “bomber” seats, and these days most of them are custom-built since the supply of military surplus seats has largely dried up. True bomber seats were made from thin, high-strength aluminum, and they were usually riveted together. While everyone likes the look of rivets, making a complex riveted structure takes an inordinate amount of precision and time.
I wanted to make a bomber seat using an easier process, so I designed a seat with the sides, bottom and back made from a single piece of metal. I added a simple reinforcement to the edge — which also gives the seat a more finished appearance. I made my seat from steel, so the joints could be easily spot or plug welded with a machine like the Multimatic® 215.
The first step was making some models from paper, working out the shape and proportions I desired. Once I finalized the design, it was simple to scale up the dimensions and do a full-sized layout.
I made a bending fixture from some scrap tubing and plate. Laying out bends can be challenging, but I devised a simple system. Rather than trying to position and clamp a piece of tubing onto sheet metal for making the bends, I placed a stop on the tube that registers the edge of the sheet metal. This makes it easy to make consistent bends, even when some are angled, like the seat back. I positioned the stop to create a 3-inch flat flange, and the tube gives a 2-inch- radius curve. If you bend the metal to 90 degrees, each side draws in 2-¼ inches, so to get a 16-inch-wide seat, I start with a blank 20-½ inches-wide.
Aircraft seats are often riddled with holes to reduce weight, and I really like this look. I decided to use oval punches for this seat, with a staggered pattern, and I spaced the holes as close as the tooling would allow. I used a J-shaped strip of metal to reinforce the edges and to cover the raw metal edge. I spot welded everything together, but the joints could be plug welded, too.
Plug welding is easily accomplished with a MIG welder or multiprocess welder, like the Multimatic 215. Once you decide where to place the welds, a hole is drilled or punched through one thickness of metal — I normally use a 5/16-inch-diameter hole for this. Next, the overlapped panels are clamped tightly together, and a weld bead is run around the edge of the hole, adding filler wire until the hole is plugged completely. Done correctly, this makes a low-profile weld, with excellent strength and very little distortion. If desired, you can sand the weld flat, making it completely invisible.
Scroll through the photos, and I’ll describe each step in the process.
I made several miniature paper mock-ups to work out the seat’s proportions.
With the design finalized, the dimensions were scaled up and transferred to a sheet of steel, including the layout for the lightening holes.
I used aircraft shears to trim the blank to size. You’ll see how important the round holes are when we make the bend between the seat bottom and back.
I’m using a beading machine to roll a step in the metal, which will make the joint flush on the inside.
I’m making a test bend in the fixture. A key feature is the stop which registers the edge of the metal (at the tip of the arrow). This ensures that all bends are the same, and it eliminates the need to move and re-clamp the fixture. With this system, the bends are positioned by the edges of the blank.
The sides of the seat bottom are parallel, but the back tapers. This is easily accomplished by bending the flanges on each segment individually.
The bend between the bottom and the back is done freehand, but it’s constrained to the area between the round relief holes in the blank.
Pins are used to align the male and female parts for the oval hole punches. Here I’m using a annular cutter to make the holes for these guide pins.
I’m using an H-frame hydraulic press with the Jamey Jordan ‘Oval Punch and Flare’ dies. These punch the hole and flare the edges in one operation.
The flush-fitted lap joints are now spot welded together.
Plug welding is another good option for making joints like this. I’m using the Auto-Set™ feature of the Multimatic 215 mutliprocess welder to get the parameters dialed in, based on the wire size and metal thickness.
To make plug welds, I punch 5/16-inch diameter holes, clamp the panels together, and then run a bead around the perimeter of the hole, adding filler metal until the hole is filled. Plug welds are fast and strong, and they offer just as much strength as a spot weld.
Now the cut line is marked for the seat sides, and they are rough-trimmed with a cordless shear. This rough trimming could also be done with a plasma cutter.
The final trimming is done with aircraft shears.
I used a sheet metal brake to bend a sharp angle in a piece of sheet metal, and then used flattening dies in the beading machine to roll the flange over to 180-degrees. This will be the cap strip for the seat edges.
The edge cap needs to be curved, and I’ve made a paper pattern to follow as I do the shaping.
The edge cap is curved by working the long flange with a shrinker and stretcher.
After the cap has been properly contoured, it needs a twist in the top corners. I’ve clamped the cap to my versatile bending fixture, and I’m hammering it around the tube to get the twist.
With the cap fitted, the ends are spot welded into place.
Here I’m using flattening dies on the beading machine to tightly crimp the edge cap to the seat.
Here’s the finished seat, and I’m delighted with the way it came out! Making the seat from a single piece of metal, and spot welding the joints really eased the construction. A seat like this can be made in a fraction of the time it would take to make a riveted aluminum bomber seat.
About Ron Covell
Ron Covell is a talented welder and metalworker in the automotive industry. Covell is a contributor for Hot Rod Network, where he has a popular column titled, "Professor Hammer's Metalworking Tips." He also owns Covell Creative Metalworking, offers instructional metalworking DVDs and hosts workshops around the country.