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Sheetmetal Bending 101

Posted in How To: Tech Qa on December 13, 2017
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Quite literally, books have been written on the topic of bending sheetmetal to form useful shapes. We don’t intend to duplicate all that knowledge here, but rather give you, the home fabricator and 4x4 nut, some information and tools to help you bend metal for whatever project you see fit.

Also, we didn’t learn to use sheetmetal or press brakes the way someone should—we just dove in head-first and learned from experience and the occasional failure. We definitely have more to learn on the topic, but we feel we have enough experience to share. We have used sheetmetal, mostly steel, to build transmission tunnel covers, bikini tops, body parts, boxes, fan shrouds, and more.

As you know, adding a bend to a piece of metal makes it much more ridged. Bending metal can be done with a sheetmetal brake, a press brake, or even a few pieces of angle iron and some clamps, or a few pliers and a bench vise. For the purposes of this article we are going to talk about using an old Chinese sheetmetal brake and a Swag Off Road 12-ton press brake with Swag Off Road press plates on a 12-ton Harbor Freight Tools shop press. So this is a simplification focused on bending about 22-gauge up to 1/4-inch for brackets, but bending sheetmetal is still complicated. You need to understand a few things about the metal and how it will react to being bent—or just bend away and hope it doesn’t fail when the going gets tough! To learn more check out the photos below and continue to educate yourself on the topic.

You may not realize it, but metal has a grain. Like wood, a metal’s grain affects its properties. The grain comes from the fact that most sheetmetal starts life as a round bar that is hot rolled or cold rolled into sheets or plates of different thicknesses. So the grain (usually somewhat visible) runs parallel to the long axis of the original metal bar. It’s generally best to bend metal perpendicular to the grain (90 degrees to it). Bending along the grain can lead to cracking and splitting of the material, or at least a weaker piece of metal.
When sheetmetal is bent it never follows a sharp or exact bend. The outside of the bend stretches and the inside compresses. The curvature along the bend is called the bend radius. All materials have a minimum bending radius below which the bend may weaken the metal. Thicker metal has a larger bend radius, and thinner metal has a smaller bend radius (unless it’s harder and more brittle, in which case you may need a larger bend radius to retain the metal’s strength and keep it from splitting). Also, if you bend with the grain of the metal a larger bend radius will result in a stronger component.
Because you cannot bend metal at an exact 90 degrees, calculating the distance between two bends and two subsequent legs of a bend requires a mathematical formula and knowing the bend radius, material composition, hardness, and material thickness. These formulas are a bit outside the scope of this article, but should be something you learn more about if you get into making multiple parts or you make something a person’s life depends on. Our plan is to bend sheetmetal for noncritical parts like interior or roof panels. To get measurements, we will make a sample bend and use it to determine outside dimensions. If you care, look up bend allowance, K-factor, and setback. That ought to keep you busy for a while.
Our buddy and fabricator extraordinaire Rob Bonney gave us this old Chinese sheetmetal brake and it’s awesome despite the rust. Bonney also gave us a primer on how to use the machine, but we’re not experts by any stretch. Still, what we’ve learned is helpful and we want to share. First step is to learn the names of some of the parts of the break. The toothlike things are called the upper bar or clamping jaw (A). This brake has fingers that allow the user to bend boxes of different sizes (inset). The clamping jaw clamps the material to be bent to the stationary bed. The bending leaf is the hinged metal at the front with two handles hanging down (B). The clamping jaw is adjusted front to back with two adjustment knobs on the back of both sides (C). Clamping force comes from tightening (pulling forward and down on) the two clamping bar handles on each side (D).
To make a bend, place the metal to be bent in the center of the brake and adjust the clamping jaw using the adjustment knobs. The clamping jaw has to be parallel to the teeth in order to ensure the bend is true (i.e., 90 degrees) all the way down the bend. The minimum space between the end of the upper jaw/clamping bar (adjusted with the two adjustment knobs on the back) and the bending leaf must be thicker than the material being bent, otherwise the break wants to act like a shear and tries to cut the metal rather than bend it. Any extra space between these two will cause a larger radius bend. With this adjustment set, you can clamp the metal in place with the clamping bar handles. Then lift up the bending leaf using the handles. The bending leaf here has counterweights to help with forming. You can bend the metal from zero degrees well past 90 degrees until the metal hits the top of the clamping jaws.
Aluminum and thin chromoly are so hard that they need a radius at the bend rather than a sharp knife’s edge or they could crack and split. Some breaks will have more of a radius machined into the clamping jaws. Alternatively you could have some small round bar or tube welded to some plate that would go between the clamping jaw and the material to be bent to increase the minimum bend radius. Here we tried to do everything wrong. We made a very sharp bend with the grain (instead of against it) to see if we could get the aluminum to crack, but not much of a crack is showing.
Hard metals can be annealed to make them softer and more malleable, which makes bending easier and lessens the chance of cracking at the bend. To anneal aluminum with an oxy-acetylene setup, first add soot by burning just acetylene in the torch. Then burn off the soot with a proper mixture, and allow the aluminum to air-cool. When bending a box or any metal with corners, a small hole at the bending points (we used 1/8-inch holes at corners) will prevent stress cracks from forming.
With our limited experience and a little time we were able to use our brake to bend up this little aluminum box. It ain’t perfect, but as they say, Rome wasn’t built in a day. We learned a ton. You can see here how we were able to use one of the tapered fingers to finish the last two bends even though our measurements (bend allowance and setback) are off.
We mentioned our 12-ton Harbor Freight Tools shop press, with the press plates and press brake kit from Swag Off Road. This thing is great for making custom tabs and brackets as well as contoured weld plates. We’ll use it for thicker materials. It’s rated to bend 6-inch pieces of 1/4-inch steel plate, and 8 inches of 3/16-inch steel plate, and can do full-length bends on 1/8-inch or thinner steel plate. Bending with this setup is pretty straightforward, and many of the above information applies.
This is the 1/4-inch plate we bent in the Swag/HFT press brake. You can see the nice 90-degree bend we achieved. This press does have a minimum span of about 4 inches. The piece has to gap for the bender to work. You can see the witness marks on the metal from the lower die (which is a modified piece of angle iron). You can make the press more versatile with Swag Off Road’s Finger Brake Goose Neck dies, and or cut pieces of smaller angle iron to drop into the bottom die.
Long before we had any kind of brake, we used a vise and a hammer to bend metal. Many other rudimentary metal brakes can easily be concocted in a pinch. You can also use these special locking pliers and an adjustable wrench to make not-so-pretty bends in metal. These methods will work, and you’ll quickly learn about how hard it is to line things up straight and how easy it is to make an out-of-plane bend.
Once you have gotten pretty good at bending metal you’ll realize how many parts can be made and made stronger just by adding a few bends.


Swag Off Road
Oregon City, OR 97045
Harbor Freight Tools

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