Steady Rests and Follower Rests Information
Lathes have been in use for centuries. The basic turning tools that rotate the workpiece while a tool fashions the wood “blank” into a finished part date back to ancient times. While wood lathes have been producing the likes of table legs, railing spindles, bowls, woodwind instruments, and my favorite baseball bats for seemingly ever, it was when metal turning became mastered in the late 18th century that the industrial revolution had begun. The main driver of adopting the lathe to turn metal was the production of gun and cannon barrels at arsenals throughout the world.
To turn a metal or wood spinning part on a lathe, you must apply enough force through the tool onto the outside diameter of the workpiece to “turn” a small amount of material to separate away from your finished part. As parts get longer with a high length to diameter ratio (think of broom handles and gun barrels), the mechanics of materials, modulus of elasticity, and deflection come into play and proper pressure cannot be maintained by the tool. When your tool deflects the workpiece, dimensional accuracies suffer and decreased tool pressure affects the quality and efficiency of the turning.
Steady rests and follower rests were developed to remedy the lathe turning deflection problem. Steady rests and follower rests hold a long workpiece steady during turning. Steady rests are mounted to the lathe bed and do not move with the lathe. They ensure concentricity, but limit the length of the supporting cut. Also, to achieve the best results in turning, vibration must be kept to a minimum. Vibration is problematic for any turning, but it is particularly problematic when turning long spindles, or hollowing out deep vessels. To reduce vibration, a steady rest provides needed support. Typically, steady rests are selected to provide support for longer cuts. Both steady rests and follower rests are used with cylindrical parts and round stock. They are also used to keep the workpiece from wobbling and to ensure that a drilled hole will be concentric with the outside diameter (OD) of the part.
Follower rests are so named because they attach to the saddle (the lathe component that holds the tool) and move along with or "follow" the lathe. Some long slender shafts that tend to whip and spring while they are being machined require the use of a follower. The follower rest is fastened to the carriage and moves with the cutting tool. The follower rest is often used when long, flexible shafts are threaded. At the completion of each threading cut, care must be taken to remove any burrs that may have formed to prevent them from causing the work to move out of alignment.
The key component to steady rests and follower rests are the jaws. The jaws have posts called quills that the work rotates on. Quills can be fixed posts or rolling elements. There are two main arrangements for the positioning of quills. Roller steady rests do not have an upper quill. They are built for workpieces into the double-digit tons range and diameters up to three meters. The weight of the workpiece is enough to keep it in contact with the rest during turning. Lighter work needs to be held in all directions; otherwise, the cutting force of the tool can lift the workpiece off of the rest. This 360 degree containment is achieved by either three or four quills. Various approaches allow the top post to be moved into place once the workpiece is positioned. These include:
- collapsible tops
- removable tops
- swivel tops
- c-forms that are open on one side
Steady rests and follower rests are very important lathe components when long and narrow parts are to be turned. Used to avoid the sagging while turning metal and other materials, they have had great impact on the advancement of many of the important products and machines used today. Transportation, defense, and power generation all rely on long shaft and barrel production. Steady rests and follower rests are a tried and true addition to many types of lathe. They can be obtained in a broad range of designs and configurations to meet the particular needs of the work at hand.
RichterLünetten / CC BY-SA 2.0 DE