The first relationship to evaluate is wall factor: the ratio between the outside diameter of the material and its wall thickness. Hence, our bending die charts include minimum wall thickness specs for OD and centerline radius. (If you're still confused on those terms, check out our Tube and Pipe Bending Basics page.) The relationship between those parameters determine whether or not you can perform a bend and if you need a mandrel to do so. To create a quality bend, many factors are at play: type (and, by extension, quality) of your material, outside diameter, wall thickness, and centerline radius. The question is how to minimize that effect. As a result, the cross-section of the bent section of the tube is flattened.” ( Machinery’s Handbook 1382) Translation: the tube takes on a slightly oval shape (and that’s okay!). This condition of tensile stress causes thinning and elongation of the wall at the outside, and the compression stress causes thickening and shortening of the inner wall. “When the tube or pipe is bent, fibers at the outside wall are in tension and fibers at the wall on the inside bend are in compression.

Whether you’re bending up mild steel for a roll cage or some wild alloy for aerospace parts, the goal of tube bending stays constant: produce smooth, round bends. To those of you who didn’t just click your browser’s back button, here we go: The Goal of Tube Bending

So without further ado, we bring you: wall factor and “D” of bend. And while we’d rather be bending a cage back in our shop right now, too, but we think you’d like to know just what’s going on when you throw a stick of material into your tube bender and wrap it around the die.

Every so often, we have to break out our book learning. We’re about to get technical-like really technical. But beneath those dirty fingernails and stained welding gloves, there’s a lot of science at work. No doubt you’ve heard people say that metalworking is “more of an art than a science.” If you’ve ever watched the learned hands of a bonafide craftsman piece together a stunning custom bike or a breathtaking bomber seat for a hot rod using only tools that he made and knowledge born only from the gallons of sweat spilled on his dirty shop floor, you know metal fabrication is an art.

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