Editing Lathe (section)

=== Metalworking ===
{{Main|Metal lathe}}

In a [[Lathe (metal)|metalworking lathe]], metal is removed from the workpiece using a hardened [[tool bit|cutting tool]], which is usually fixed to a solid moveable mounting, either a tool-post or a turret, which is then moved against the workpiece using handwheels or computer-controlled motors. These cutting tools come in a wide range of sizes and shapes, depending upon their application. Some common styles are diamond, round, square and triangular.

The tool-post is operated by lead-screws that can accurately position the tool in a variety of planes. The tool-post may be driven manually or automatically to produce the roughing and finishing cuts required to ''turn'' the workpiece to the desired shape and dimensions, or for cutting [[screw thread|threads]], [[worm gear]]s, etc. [[Cutting fluid]] may also be pumped to the cutting site to provide cooling, lubrication and clearing of [[swarf]] from the workpiece. Some [[Lathe (metal)#CNC lathe|lathes]] may be operated under control of a [[computer]] for [[mass production]] of parts (see "[[CNC|Computer numerical control]]").

Manually controlled metalworking lathes are commonly provided with a variable-ratio gear-train to drive the main lead-screw. This enables different [[Screw thread#Lead, pitch, and starts|thread pitches]] to be cut. On some older lathes or more affordable new lathes, the gear trains are changed by swapping gears with various numbers of teeth onto or off of the shafts, while more modern or expensive manually controlled lathes have a '''quick-change box''' to provide commonly used ratios by the operation of a lever. CNC lathes use computers and servomechanisms to regulate the rates of movement.

On manually controlled lathes, the thread pitches that can be cut are, in some ways, determined by the pitch of the lead-screw: A lathe with a [[metre|metric]] lead-screw will readily cut metric threads (including [[British Association screw threads|BA]]), while one with an imperial lead-screw will readily cut [[Imperial unit#Measures of length|imperial-unit]]-based threads such as [[British Standard Whitworth|BSW]] or [[Unified Thread Standard|UTS]] (UNF, UNC). This limitation is not insurmountable, because a 127-tooth gear, called a transposing gear, is used to translate between metric and inch thread pitches. However, this is optional equipment that many lathe owners do not own. It is also a larger change-wheel than the others, and on some lathes may be larger than the change-wheel mounting banjo is capable of mounting.

The workpiece may be supported between a pair of points called [[Lathe center|centres]], or it may be bolted to a faceplate or held in a [[Chuck (engineering)|chuck]]. A chuck has movable jaws that can grip the workpiece securely.

There are some effects on material properties when using a metalworking lathe. There are few chemical or physical effects, but there are many mechanical effects, which include residual stress, micro-cracks, work-hardening, and tempering in hardened materials.