Cutting and bending sheet metal

Light-gauge metal can be easily cut using snips. These may have straight or curved blades. 

Where larger sheets are required to be cut with straight edges, the guillotine is used. 

Sheet widths of 600 mm x 2 mm thick and up to 1200 mm x 1.6 mm thick can be accommodated in treadle-operated guillotines, Fig. 4.3. These have a moving top blade, which is operated by a foot treadle, and a spring which returns the blade to the top of its stroke. The table is provided with guides, to maintain the cut edges square, and adjustable stops to provide a constant size over a number of components. When the treadle is operated, a clamp descends to hold the work in 

When holes are to be cut in sheet metal, up to 16 SWG, this can be done simply and effectively using a Q-Max sheet metal punch as shown in Fig. 4.4. A pilot hole is drilled in the correct position, the screw is inserted with the punch and die on either side of the sheet, and the screw is tightened. The metal is sheared giving a correct size and shape of hole in the required position. 

Where a number of components require the same size hole in the same position, it may be economical to manufacture a punch and die for the operation. The operation is carried out on a fly press. Fig. 4.5, with the punch, which is the size and shape of the hole required, fitted in the moving part of the press. The die, which contains a hole the same shape as the punch, but slightly larger to give clearance, is clamped to the table directly in line with the punch. When the handle of the fly press is rotated, the punch descends and a sheet of metal inserted between the punch and die will have a piece removed the same shape as the punch. Fig. 4.6. 

With the use of simple tools, the fly press can also be used for bending small components. Fig. 4.7. The top tool is fixed to the moving part and the bottom tool, correctly positioned under the top tool, is fixed to the table of the press. Metal bent in this way will spring back slightly, and to allow for this the angle of the tool is made less than 90°. In the case of mild steel, an angle of 88° is sufficient for the component to spring back to 90°. 

The simplest bends can be produced by holding the component in a vice and bending it over using a soft hammer. If the component is wider than the vice jaws, it can be clamped between metal bars. Unless a radius is put on one of the bars, this method produces a sharp inside corner, which may not always be desirable. 

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