How are parts machined on a lathe?

Machining operations can be carried out on the various machine tools, from the most conventional to the most complex ones that incorporate CNC technology. How are parts machined on a lathe? What type of operations can this machine perform?

What is the machining of parts on a lathe?

The transformation of metals into parts is known as machining. For raw metal to become a part (bars, tubes, plates, screws, nuts and even tables and chairs), the metal must undergo different operations. Thanks to advances in technology, today there are many machines capable of carrying out different processes, some of them simultaneously.

There are three types of machining: by swarf removal, without swarf removal and by abrasion. The machining of parts on a lathe, milling machine and drilling machine belongs to the first type. These are processes in which a special cutting tool removes the surplus material from a part until it has the desired shape. The surplus metal waste is known as swarf.

Machining without swarf removal is carried out on machines such as presses; on this equipment the part is not cut but deformed or transformed into a new one. They are used for machining metal plates, flat bars and other sections; folding machines or tube benders also do this work. Finally, abrasive machining is a technique in which the cutting tool, called a grinding wheel, is made of abrasive materials (grains and binders), capable of removing small amounts of material. Grinding machines carry out this type of machining.

What is a lathe?

Machining on a lathe consists of carrying out operations on this machine tool, the oldest of all, to shape metal parts by swarf removal. But what is a lathe and why is it so important for industry? The lathe is a large stationary machine that makes it possible to machine geometric parts of revolution.

Parts on the lathe are said to be parts of revolution because they are placed on the chuck or headstock of the machine and rotate at high speed on their own axis. While the part rotates, a carriage pushes the cutting tool of the machine in a controlled movement. When the tool and the part come into contact, swarf removal takes place.

Types of lathe

The lathe is not a single tool; there are different types of this machine to carry out different machining jobs. The most widely used types of lathe today are:

• Centre or mechanical. The centre lathe is the «basic» lathe model from which all the other types of lathe evolved and were created. New tools were added to the ancient lathe, which dates back centuries, until the centre lathe was achieved, which in turn was adapted to create different machines.
• Copying lathe. It uses a hydraulic and electronic system for machining on the lathe according to the characteristics of the workpiece; in addition, a template is followed that reproduces a replica on the workpiece.
• Turret. Machining parts on a turret lathe makes it possible to work with several tools at the same time. This makes it possible to reduce production time. They are used to make bushes.
• Automatic. This type of lathe is characterised by completely automated processes, including the machine's feeding system. They use one or several spindles.
• Vertical. Machining on a vertical lathe is intended for large parts that are held on the machine by jaw chucks.
• CNC. These are the most advanced lathes, as they incorporate computer numerical control technology. They include a computer, which is responsible for determining the machining parameters (cutting speed, depth of cut, etc.).

Machining jobs on a lathe

Various machining operations can be carried out on parts on a lathe. It all depends on the lathe you use, as well as the type of work you want to do on the part. Some of the machining operations on a lathe are:

• Straight turning. This is one of the most common jobs and is used to shape the outside of parts or reduce their diameter. There is also internal straight turning.
• Facing. Facing makes it possible to machine the front of a part. For facing, the tool and the carriage must move transversely to the axis of rotation.
• Knurling. The part is given a rough surface.
• Drilling. A drill bit is used to drill holes.
• Reaming. To obtain precision holes with a good finish.
• Threading. There can be internal threading and external threading, for example, for machining screws and nuts.
• Taper turning. It consists of using the compound slide or carriage to shape tapered surfaces.
• Spherical turning. For more complex parts of a round or curved shape.