What is a horizontal lathe and how does it work?

The horizontal lathe, also called a centre lathe, is a machine tool of great use in machining workshops thanks to its high productivity. The processes carried out with this machine offer quality results.

What is the horizontal or centre lathe?

The horizontal-bed lathe is one of the most common machine tools and operates, as its name indicates, horizontally or in parallel, because the carriages that make it up follow a longitudinal and cross movement to machine cylindrical parts. This type of lathe is characterised by the fact that many machining operations can be carried out on it, in addition to turning and straight turning; here we find cutting, grooving, threading, parting off, boring, etc.

This is considered to be the lathe that evolved from the old lathe, as new components and parts were added to it until it became one of the most common and useful machines for workshops. However, with the advent of new technologies, this type of lathe is nowadays only used for very specific or one-off jobs. In addition, operating these lathes requires the presence of expert lathe operators, since manual handling of the carriages demands a great deal of precision.

It is also very important for operators to use the appropriate PPE when using this machine. For example, protective goggles and specific work clothing that cannot catch on the machine, in order to avoid accidents.

Parts of the centre lathe

All lathes have the same components; however, on the centre lathe, these may be slightly modified. A lathe has five fundamental parts:

• Bed, which serves as the support. On its upper part, guideways are fitted that act as rails for the movement of the headstock and the carriage
• Fixed headstock, where the gears and pulleys whose purpose is to drive the workpiece are held. The headstock, in turn, consists of the motor, the spindle and the selectors for speed, feed unit and feed direction. This component serves to support and rotate the workpiece, which is held in the spindle.
• Tailstock, an element that serves as a support point and for positioning the workpieces that are machined between centres; in addition, drill bits and drill chucks for drilling can be fitted here.
• Tool carriage, made up of a main carriage, which moves in the axial direction; in addition, it comprises the cross slide which, as its name indicates, follows transverse movements. On the centre lathe, unlike other types of lathes, there is a third carriage: the swivelling compound slide. This third carriage consists of a base, a top slide and a tool turret. It can be oriented in any direction.
• Chuck or rotating head, whose function is to hold the workpiece. There are different types of chucks on the market and each workshop can choose the one that best suits its machining needs.

Operation of the horizontal lathe

This type of lathe is easy to operate. The workpiece must be firmly held in the rotating chuck. For this, a series of strong-gripping clamps are used that prevent the workpiece from moving during the machining process. The carriages on this machine can be manual, but there are also motor-driven ones; lathes that use motorised carriages tend to be large.

The horizontal lathe is very stable, and that is one of its great advantages; however, the configuration of its tools is somewhat limited. Even so, lathes with this type of bed make it possible to load and unload large workpieces. In addition, thanks to the small space between the bed and the tailstock, workpieces can rotate at larger diameters.

Threading, a unique function of centre lathes

The threading of parts can be carried out on a numerically controlled (CNC) lathe, but it is also possible to do this machining on a centre lathe. On horizontal-bed lathes, this is achieved using the Norton gearbox. Threading is undoubtedly one of the most common tasks on centre lathes because threads of different sizes and pitches, both external (made on shafts) and internal (made on nuts), can be created. On manual horizontal-bed lathes, this is possible thanks to the aforementioned Norton gearbox. The Norton gearbox was invented in 1890 and, when it was incorporated into lathes, it represented a major advance; thanks to this gearbox, a solution was found to the manual changing of gears to set the pitches of the parts to be threaded. The gearbox is made up of several sliding gear trains, but there are also gearboxes with a tumbler gear train and a cone of gears. The gearbox connects the movement of the machine tool's headstock to the tool carriage, where a leadscrew is located. But why is threading possible? Because this gearbox allows the manipulation of several levers that allow multiple carriage feed rates; this makes it possible to thread different types of thread pitch.