How to use a fixed steady rest on a lathe

The lathe is a very versatile machine tool, since it can machine through different processes such as straight turning, drilling or grooving; however, the productivity and versatility of these machines can be increased by using one of the clamping and support accessories such as the fixed steady rest for the lathe.

What is a lathe fixed steady rest?

Although lathes are very versatile and accept almost any workpiece for machining, the size of the workpiece is a limitation. Lathes are very easy-to-use machines in which workpieces are held on a shaft and rotate at high speed, while the cutting tools approach their surface to remove the surplus material in the form of swarf. But for the machining process to be successful, the workpiece must be held firmly in the lathe chuck, and various clamping and workholding systems are used for this.

However, when the workpiece has longer dimensions than expected, other support systems such as the lathe fixed steady rest are needed; this is one of the many accessories lathes have, which can be divided into two:

• Clamping systems, support and drive. This category includes lathe centres, chucks, spindles, mandrels, as well as travelling steady rests and fixed steady rests for the lathe.
• Tool-holding devices for cutting tools, for their part, refer to different types of toolholders (straight and angled); for threading, internal turning, boring bars, assemblies for quick tool changing, and so on.

Characteristics of the lathe fixed steady rest

The lathe fixed steady rest is used to support long workpieces in the chuck or between the lathe centres. The steady rest is positioned and aligned with the parallel guideways of the lathe, regardless of which part of the bed the accessory is placed on; however, it is essential that the steady rest leaves clear the travel of the machine's carriage, which has to move along the guideways in order to machine the workpiece.

Lathe steady rests can be fixed or travelling. Travelling ones, unlike fixed ones, are mounted on the saddle and move along with the longitudinal carriage, preventing the workpiece from moving away from the working range of the cutting tool.

One feature of the steady rest is that it can be combined with other clamping systems such as the one used between centres to machine very long workpieces. This type of “combined” clamping can be used on lathes, but also on the universal grinding machine. When should you use it? When the overhang (rigid structure of the workpiece) is eight times its diameter, or when the workpieces are very thin. In these cases, the workpieces are placed in the machine between the centre, the tailstock and the fixed steady rest.

The fixed steady rest allows the workpiece to be machined without its material bending or suffering deformation from the feed movement of the tool, when the workpiece is of excessive length. Steady rests are characterised by having two or three support points and, like clamping between centres, they need a lathe dog that transmits the movement to the workpiece.

Holding workpieces using steady rests

Steady rests have one particular feature: their clamping is secure, but not very robust, so they are usually used for straight turning. However, using fixed steady rests allows perfect centring and lets you place and remove the workpiece without losing its concentricity. That said, the steady rest can leave a mark on the surface of the workpiece, and setting it up is rather laborious for operators.

The first step if you want to use the lathe fixed steady rest is to fit the accessory to the machine tool. A lathe dog is then fitted to the workpiece to be machined ; this is what transmits the movement, in this case the rotation of the chuck, to the workpiece. The movement is transmitted from the lathe dog to the workpiece through a threaded stem on the driver plate.

The steady rest is opened and the workpiece is rested on it. The workpiece is then clamped between the centre and the tailstock. The fixed steady rest is closed and the supports are adjusted on the workpiece until you are sure it is properly centred. It is important to note that this type of steady rest has an open C design, with three contact points on most of them. These steady rests are fixed along the Z axis and a mechanical clamp is placed where the steady rest is fitted. The steady rest must be able to withstand the action of the cutting forces and stop the workpiece from moving.