To the outsider, making a custom metal fabrication seems pretty straightforward. And indeed it is, if you don’t care how your trailer rub-rails look or whether those side brackets hold your toolbox secure. Nearly anyone can cut and bend, but doing it well takes a deal of finesse. The key is having metal blanks that are not only cut to the right size, but cut square. Get them right and a high-quality fabrication is (almost) guaranteed. Here’s a little about how we cut those blanks, in the hope that you’ll appreciate the “shear” artistry involved!
How it Works
We have two metal shearing machines; a 12′ wide Wysong and a 10′ wide Accurshear. Shears are specified in terms of what thickness of mild steel they can cut, and for ours that’s 1/4”. Of course, they’ll cut anything – stainless, aluminum, copper – providing the machine has the strength.
Industrial metal shears work the same as household scissors. There are two blades, one fixed and one that moves, and they’re slightly offset. The moving blade is inclined so the cut starts at one side and moves across to the other. As the moving blade pushes down, the metal first bends then fractures, which is why sheared metal edges have a slight radius.
The cleaner this edge, the less finishing is needed after shearing and the better the fabrication goes together. Two features of the machine ensure a clean edge: the hold-down mechanism and the gap between the two blades. The hold-down does exactly that – it holds the sheet while it’s being cut, minimizing bending and twisting. The gap depends on the straightness of the blades and the condition of the machine. We buy quality tooling and look after our machines so that the gap is small and uniform.
Why Quality Shearing is Important
On the subject of quality, to help us cut square, behind the blades the shears have a “backgauge.” This is a stop that the metal sheet is pushed up against. The distance from blade to backgauge sets the size of the cut blank. Again, it’s important to maintain the machine so that the backgauge is parallel to the blade.
After metal shearing the next step is usually to cut out or “notch” the corners. This makes room for the edges of the blank to be folded up, which adds stiffness to the piece. If the blank’s not perfectly square and to size it won’t fold quite right, and that’s why metal shearing is such an important first step.