What is a mechanical lathe?

The mechanical lathe is the oldest machine tool in existence. The first lathe is believed to have appeared between 1000-850 BC in Egypt. Since then, this machine tool has done nothing but evolve and adapt to the needs of the metalworking industry. But what is a lathe and what are its most important parts?

Features of the mechanical lathe

Although the lathe is the first machine tool that was invented, it was not until the Industrial Revolution that it began to be perfected into the equipment we know today. It was in the 17th century that this machine was adapted to be able to shape metal parts and in the 18th century it was achieved, for the first time, that the mechanical lathe could produce parts in series and with great precision.

You will be surprised to learn that as early as 1780 a lathe with a sliding tool holder was created; in 1797 the cutting tool of this machine was already able to advance at constant speed and between 1820 and 1840 the copying and turret lathes were invented, while in 1839 the centre lathe was patented for the first time for straight turning and threading. By 1890 the famous Norton gearbox was fitted to centre lathes, allowing gears to be changed manually and the thread pitches of the parts to be set.

What is a mechanical lathe and why is it so important for the machining industry? The mechanical lathe is defined as a group of machine tools capable of machining geometric parts of revolution. For a mechanical lathe to work, the workpiece must rotate on its own axis at high speed, so the workpiece is held in the headstock or between two centres (tailstock). While the workpiece rotates, the cutting tool approaches its surface in a controlled feed movement. When the cutting tool reaches the workpiece, removal of material takes place in the form of small flakes called swarf.

Parts of the mechanical lathe

The mechanical lathe, which is one of the most widely used machine tools in machining workshops, has the following parts:

• Bed. This is the base of the lathe and supports the other parts. On top of it sit a series of guideways that allow the movable head, the main carriage and the tailstock to slide. The workpiece to be machined is placed on these.
• Fixed headstock. The fixed headstock of the mechanical lathe houses the gears and pulleys, which drive the workpiece to be machined as well as the feed units. The fixed headstock contains the motor, the spindle, the speed selector, and the feed unit and feed direction selectors. The fixed headstock supports and rotates the workpiece.
• Tailstock. This is a machining element used in some jobs; it serves to support and position parts that are machined between two centres. The tailstock is movable and can be fixed in different positions on the bed.
• Carriage. It is made up of a main carriage, which holds the main tool and gives it axial movement. It also has a cross slide which, as its name indicates, moves transversely across the main carriage, in a radial direction. On some lathes, such as the centre lathe, there is a third, swivelling carriage; this carriage consists of a compound slide, a base and a tool-holder turret.
• Chuck or rotating head. This part of the mechanical lathe holds the workpiece so that it rotates on its own axis while machining is carried out. There are different types of chuck: four-jaw, three-jaw, universal, etc.
• Norton gearbox. This part of the lathe is used to select the feeds and thread pitches by means of a series of levers that work with gears located inside the box itself.

Workholding elements

All machine tools, whichever they may be, must incorporate a workpiece clamping system. Why is it so important? Clamping is indispensable in all machining operations because, through various tools and accessories, it makes it possible to fix the workpiece firmly in a chuck so that it does not move while machining is carried out.

Some machine tools already include clamping systems as standard, but they also accept accessories that can be fitted according to machining needs. On the mechanical lathe, these accessories can be:

• Clamping chucks. They can be of two types: universal-jaw and soft-jaw. There are also three-, four- or six-jaw chucks. The chuck fixes the workpiece to the machine temporarily and transmits the machining motion.
• Centres or points. These accessories hold the workpiece in the headstock and in the tailstock.
• Driving pins. The pin is fixed in the chuck of the mechanical lathe and in the workpiece. They are responsible for transmitting the motion when the workpiece is mounted between centres.
• Steady rests. The most common is the fixed one. This accessory supports the end of the workpiece when machining between centres or with a tailstock is impossible. The movable steady rest is another type of steady rest, mounted on the carriage, and is ideal for machining large parts.
• Tool-holder turret.
• Driving plates and independent-jaw chucks. The former is used to machine parts that, because of their characteristics, cannot easily be mounted in the headstock. The latter has four jaws, acting like vice jaws, independent of one another.