Engine turning

Engine turning is a form of ornamental turning. The finishing technique may use lathes or engines to produce a pattern. Aluminium is often the metal chosen to decorate. The technique has been used in various industries, including aircraft and document verification.

Description
Engine turning is a form of ornamental turning. The technique geometrically applies a single-point cutting tool to produce a decorative metal surface finish pattern.

Traditionally, engine turning referred to Guilloché engraving. In the 20th century, it also came to refer to the different process of Perlée (also known as spotting, jewelling, perlage), which is a fine geometric pattern of overlapping circles abraded onto the surface.

Equipment
Guilloché engine turning may be done with various machines, including rose engines, straight-line engines, brocade engines, and ornamental turning lathes. Perlage uses an abrasive rotating disk or dowel.

Material
Aluminium is often the metal chosen to decorate with jewelling, but any appropriate surface can be finely machined to produce intricate repetitive patterns that offer reflective interest and fine detail.

Aircraft
Perlée-style engine turning was used on the sheet metal panels of the engine cowling (nose) of Charles Lindbergh's aircraft, the Spirit of St. Louis.

The sheet metal parts of the World War I Fokker Eindecker fighters aircraft series, especially around the engine cowl and associated sheet metal, are noted for having a "dragged" form of engine turning entirely covering them. The tool creating the "swirls" was repeatedly moved along a short, irregular path each time while pressed against the metal, to create the intricate appearance that was characteristic of the aircraft's sheet-metal parts. It is partly surmised to have been a mechanical method to "clad" a duralumin-alloy sheet-metal panel with a layer of pure aluminum, for corrosion protection.

Automobiles
In the 1920s and 1930s, automobile parts such as valve covers, which are right on top of the engine, were also decorated with perlage engine turning. Similarly, dashboards or the instrument panel of the same were often perlaged. Customizers also would similarly decorate their vehicles with perlage engine-turned panels.

Documents
Engravings produced by engine turning are often incorporated into the design of bank notes, and other high-value documents, to make counterfeiting difficult. The resulting graphics are called guillochés.

Firearms
Perlage engine turning is also used on various firearm components to prevent corrosion by holding traces of oil and lubricants on the surface, in turn to a polished surface resulting in a smooth operation.

Watchmaking
Guilloché and perlage are traditional techniques used in have been used in the watch-making.