Knurling

Knurling is a manufacturing process, typically conducted on a lathe, whereby a pattern of straight, angled or crossed lines is rolled into the material. Knurling is a manufacturing process, typically conducted on a lathe, whereby a pattern of straight, angled or crossed lines is rolled into the material. The terms knurl and knurled are from an earlier knur ‘knot in wood’ and the diminutive -le, from Middle English knaur or knarre ‘knot in wood; twisted rock; crag’. This descends from Old English cnearra but the vowel in Middle English may have been influenced by Old Norse knǫrr ‘merchant ship’ which was known as cnearr in Old English. The modern gnarl is a back-formation of gnarled which itself is first attested in Shakespeare’s works and is apparently a variant of knurled. The operation is performed for producing indentations on a part of a workpiece. Knurling allows hands or fingers to get a better grip on the knurled object than would be provided by the originally smooth metal surface. Occasionally, the knurled pattern is a series of straight ridges or a helix of 'straight' ridges rather than the more-usual criss-cross pattern. Knurling may also be used as a repair method: because a rolled-in knurled surface has raised areas surrounding the depressed areas, these raised areas can make up for wear on the part. In the days when labor was cheap and parts expensive, this repair method was feasible on pistons of internal combustion engines, where the skirt of a worn piston was expanded back to the nominal size using a knurling process. As auto parts have become less expensive, knurling has become less prevalent than it once was, and is specifically discouraged by performance engine builders.