English Wheel

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An english wheel showing four interchangable lower rollers, the larger fixed upper roller, the pressure adjustment screw and a quick release mechanism

The English Wheel is a manually operated metal working apparatus that allows a craftsman to form smooth, compound curves from flat sheets of metal, such as aluminium or mild steel.

The machine is made of steel and is shaped like a large, closed letter "C". At the ends of the C, there are two wheels. The wheel on the top is called the rolling wheel, while the wheel on the bottom is called the anvil wheel. (Some references refer to the wheels by their position: upper wheel and lower wheel.) The anvil wheel will usually have a smaller radius than the rolling wheel. While larger machines exist, the rolling wheel is usually 8 cm (3 inches) wide or less, and usually 25 cm (9 inches) in diameter, or less.

The rolling (top) wheel will be flat in cross section, while the anvil (bottom) wheel will be domed.

The depth of the C-shaped frame is called the throat. The largest machines have throat sizes of 120 cm (48 inches), while smaller machines have throat sizes of about 60 cm (24 inches). The C stands vertically and is supported by a metal frame. If this frame is made from braced box section tubular steel, it usually has rollers so the machine may be moved throughout the shop or stored conveniently. If it is more traditionally made from cast iron or steel, it is usually bolted to the floor. The throat size determines the largest sheet size that can be placed into the machine and worked easily. Because the machine works by an amount of pressure between the wheels through the material, and because that pressure will change as the material becomes thinner, the lower jaw of the frame that holds the anvil roller is adjustable. It may move with a hydraulic jack or a screw jack. As the material thins, the pressure must be adjusted to compensate.

The wheels are set to meet by manual adjustment. The machine is used by repeatedly passing the sheet metal between the anvil wheel and the rolling wheel. This stretches the material and causes it to become thinner. As the material stretches, it is formed into a convex surface over the anvil wheel. The radius of the surface after working, depends on the amount of stretching of the sheet metal in middle of the work piece, relative to the amount of metal at the edge of the work piece. If the middle is overstretched it is possible to recover the shape by wheeling the edge. The amount of stretch put into the work piece is determined by the pressure in the contact area, (which varies with the radius of the dome on the anvil wheel and the pressure on the adjuster screw) and the number of, (ideally overlapping) wheeling passes. A properly equipped machine will have an assortment of anvil wheels. Anvil wheels, like dollys used with hammers in panel beating, (which are also known as anvils), should be used to match the desired crown / curvature of the work piece.

The operator will make several passes over an area on the sheet in order to form the area correctly. He may make additional passes with different wheels and in different directions (at 90 degrees for a simple double curvature shape, for example) in order to achieve the desired shape. Using the correct pressure and appropriate anvil wheel shape and pattern of wheeling passes, makes the use of the machine something of an art in order to produce a piece of steel, aluminium or other sheet metal with a particular physical shape. Too much pressure will result in a finished product that is undulating, marred and stressed, while too little pressure causes work to progress very slowly. Working with an English wheel is easier for many applications when compared to manually hammering the steel, and is usually more appropriate for smooth curves than using an pneumatic hammer, it may used for planishing to a smooth final finish after these processes.