Crash Course in Machining – Turning

Turning is a machining process in which a single-point tool removes material from the surface of a rotating workpiece. The tool is fed linearly in a direction parallel to the axis of rotation to generate a cylindrical geometry. Turning is traditionally carried out on a machine tool called a lathe, which provides power to turn the part at a given rotational speed and to feed the tool at a specified rate and depth of cut.

CNC turning of a pulley

A variety of other machining operations can be performed on a lathe in addition to turning; these include the following:

  • Facing – The tool is fed radially into the rotating work on one end to create a flat surface on the end. The direction of movement of the turning tool depends on the type of machining, the cutting edge form and the tool position, as well as on the workpiece geometry (hollow part, solid). In roughing, a motion from the outside to the inside is preferred, whereas in finishing the reverse is true.
  • Taper turning – Taper turning is a cylindrical turning procedure in which the diameter to be generated is constantly changing. This method is used to produce conical shafts.
  • Contour turning – Instead of feeding the tool along a straight line parallel to the axis of rotation as in turning, the tool follows a contour that is other than straight, thus creating a contoured form in the turned part.
  • Form turning – In this operation, sometimes called forming, the tool has a shape that is imparted to the work by plunging the tool radially into the work.
  • Chamfering – The cutting edge of the tool is used to cut an angle on the corner of the cylinder, forming what is called a ‘‘chamfer.’’
  • Cutoff – The tool is fed radially into the rotating work at some location along its length to cut off the end of the part. This operation is sometimes referred to as parting.
  • Threading – A pointed tool is fed linearly across the outside surface of the rotating workpart in a direction parallel to the axis of rotation at a large effective feed rate, thus creating threads in the cylinder. In a manual lathe, the exact feed required for thread cutting is created by the lead screw and the feed gear mechanism. In a CNC lathe, the feed is adjusted through an electrical connection between the main spindle and the feed driving motor.
  • Boring – A single-point tool is fed linearly, parallel to the axis of rotation, on the inside diameter of an existing hole in the part.
  • Drilling – Drilling can be performed on a lathe by feeding the drill into the rotating work along its axis. Reaming can be performed in a similar way.
  • Knurling – This is not a machining operation because it does not involve cutting of material. Instead, it is a metal forming operation used to produce a regular crosshatched pattern in the work surface.

The dimensional accuracy values that can be achieved with finish turning range from IT7 to IT8. With fine finishing, given optimal turning conditions, accuracy values of IT6 are feasible.

Turning operations sketch
Machining operations other than turning that are performed on a lathe: (a) facing, (b) taper turning, (c) contour turning, (d) form turning, (e) chamfering, (f) cutoff, (g) threading, (h) boring, (i) drilling, and (j) knurling.

At CNC Proto we specialise in the machining of non-ferrous metals, mostly 6000 and 7000 series aluminium alloys, and engineering plastics. You can see a list of our most used alloys in our Services page. If your parts require a specific aluminium alloy other than the ones listed, feel free to let us know on our Quote Request form!

For more articles on CNC machining, materials and design of machined parts, be sure to check our Resource Library.

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Fernando Duarte Ramos

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With an MSc. in Mechanical Engineering, Fernando has worked 8 years at CERN designing and building the next generation of particle detectors alongside top European engineers and physicists. Being passionate about CNC machining, he started CNC Proto, an online CNC machining service in Europe dedicated to providing fast turnaround, high quality parts at a competitive cost. Learn more About Us

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