The metal spinning process starts when a formed block is mounted in the drive section of a lathe whilst a pre-sized metal disk is then clamped against the block by a pressure pad, which is attached to the tailstock. The block and workpiece are then rotated together at high speeds with a localized force applied to the workpiece to cause it to flow over the block. This force is usually applied via various levered tools.
Simple workpieces are just removed from the block, but more complex shapes may require a multi-piece block. Extremely complex shapes can be spun over ice forms, which then melt away after spinning. As a result of the final diameter of the workpiece always being less than the starting diameter the workpiece must thicken, elongated radially, or buckle circumferentially.
There is a more involved process known as reducing or necking, that allows a spun workpiece to include reentrant geometries. If surface finish and form are not critical then the workpiece is "spun on air"; no mandrel is used. If the finish or form are critical then an eccentrically mounted mandrel is used.
"Hot Spinning" - this process involves spinning a piece of metal on a lathe with high heat from a torch. Once heated, the metal is shaped as the lathe presses against the heated surface forcing it to distort as it spins. Parts can then be shaped or necked down to a smaller diameter with little force exerted, providing a seamless shoulder.
The basic hand metal spinning tool is called a spoon, though many other tools (commercially produced, ad hoc, or improvised) can be used to effect varied results. Spinning tools can be constructed of hardened steel with aluminium or solid brass for spinning stainless steel or mild steel.
Some metal spinning tools are allowed to spin on bearings during the forming process to reduce friction and heating of the tool, extend the tool life and improve surface finish. Rotating tools may also be coated with a thin film of ceramic to prolong tool life.
Commercially, rollers mounted on the end of levers are generally used to form the material down to the mandrel in both hand spinning and CNC metal spinning. Rollers vary in diameter and thickness depending the intended use. The wider the roller the smoother the surface of the spinning; the thinner rollers can be used to form smaller radii.
Cutting of the metal is done by hand held cutters, often foot long hollow bars with tool steel shaped/sharpened files attached. In CNC applications, carbide or tool steel cut-off tools are used.
The mandrel does not incur excessive forces so it can be made from wood, plastic, or ice. For hard materials or high volume use, the mandrel is usually made of metal.