What is a lathe steady rest?

The lathe is a machine tool for machining workpieces by rotation, through metal cutting. On the lathe, the workpiece turns on its own axis, while the cutting tool moves until it reaches the surface of that workpiece. When the cutting tool comes into contact with the surface of the workpiece, the excess material is removed in the form of swarf. One of the elements needed for correct machining is the lathe steady rest.

Workholding systems: the lathe steady rest

For workpieces to be machined properly, several requirements must be met. Beyond the machining itself, using the right tools and specific programs, it is essential that the workpieces are held very securely in the machine tool. There are different types of workholding systems that stop the workpiece from moving out of place while the machine is working. These include jaws, but also steady rests.

The lathe steady rest is a complementary workholding device that acts as a support for workpieces. These devices are used when long round workpieces are being machined; the main purpose of steady rests is to prevent the workpieces from deforming while the necessary pressure is applied for turning operations.

General information about lathes

Before going into detail about the lathe steady rest, it is important to establish what a lathe is and what it consists of. Broadly speaking, the lathe is a machine tool that allows workpieces to be machined through various processes; a lathe can thread, cut off, make holes or drill, turn, rough and groove workpieces. The workpiece is held in the headstock or chuck of the machine and made to rotate on its own axis. While the workpiece rotates, one or more cutting tools approach the surface of the workpiece in a feed movement.

When the tool reaches the surface of the workpiece, the excess material is removed in the form of thin strips called swarf. On lathes, the cutting tool is mounted on a carriage that slides on guides or rails parallel to the axis of the workpiece, the X axis. On the carriage, in turn, there is another carriage that moves along the Z axis and follows a direction radial to the workpiece. On some lathes there is a third carriage, called a compound slide , which can be tilted.

There are different types of lathes in industry: centre lathes, copying lathes, computer numerical control (CNC) lathes, automatic lathes and so on. How each of them works depends on its specification, but if there is one thing all lathes have in common, it is the workholding systems they use. These systems, which include the lathe steady rest, aim to keep the workpiece in place so that machining can be precise.

Lathe accessories

The lathe, like many other machine tools, has auxiliary systems that make turning operations easier to carry out and ensure quality results. There are many lathe accessories, including workholding systems and supports. Some of these are:

• Universal jaw chuck, which allows the workpiece to be held on the headstock.
• Soft-jaw chuck, an accessory that holds the workpiece on the headstock by a surface that has already been finished.
• Driver plate, for workpieces that are difficult to hold.
• Independent jaw chuck, which holds workpieces with four jaws that are independent of one another.
• Fixed support or steady rest, which allows one end of the workpiece to be held when the tailstock cannot be used.
• Travelling support or travelling steady, which is mounted on the carriage and allows long workpieces to be held close to the cutting point.

The automatic lathe, for its part, is characterised in that the axial movement is provided by the lathe headstock. In automatic lathes, also called “sliding headstock” or Swiss-type lathes, the headstock moves back with the collet open and, when the collet is closed, produces a feed movement of the bar for machining the workpiece, while the tool does not move axially.

It is thanks to the lathe steady rest that workpieces of great length can be machined regardless of their diameter.

Steady rests in the different turning operations

Cylindrical turning

Cylindrical turning is the internal and external machining of cylindrical bodies. To guarantee the quality of this type of work, the lathe must be well adjusted in terms of alignment and concentricity. Workpieces for cylindrical turning can be held in the jaw chuck (when they are short); but they can also be held between centres with a driving pin. When the workpieces are large and heavy, it is most advisable to hold them with a fixed or travelling steady.

Boring

When cylindrical turning is carried out inside a hollow workpiece, it is called boring. When a long cylindrical workpiece is to be machined, one of the holding and support devices is used, such as chucks and fixed or travelling steady rests.