The lathe is one of the oldest and most significant tools in modern machining, and it's actually known as the mother of all machining tools. The ancient lathes (1300 BC) were used to process wood, with modern lathes powered by electric motors and servomechanisms, mostly used for metalworking and processing plastic components.

Regardless, all aforementioned applications have one thing in common: the need to hold the workpiece tightly and securely to enable easy machining. As such, many work-holding devices are used to make the machining process on lathe machines easier and safer.

What are Work-holding Devices Used For?

Workholding devices are used to correctly position the workpiece and protect it from movement caused by forces exerted by the machining tools during the machining operations. A workholding tool is any tool used to hold a workpiece securely in place relative to the position of the machine tool so that the workpiece can withstand the stresses of cutting and machining without causing damage to the workpiece, cutting tool, or lathe machine itself.

Types of Work-holding Devices in Lathe Machines

We already established that securing the workholding piece and preventing its movement relative to the machine is paramount in facilitating easy and precise machining. There are several types of workholding devices used for this purpose:

Chucks

Chucks are arguably the most used kind of workholding mechanism for lathes. They are quick and precise and function effectively with most workpiece types. There are four basic types of chucks:

• Three Jaw Chucks — These are also known as three-jaw self-centering chucks. They have a cylindrical body with three radially fastened jaws at the front for effective clamping. This kind of chuck is typically used to handle workpieces with regular shapes during turning operations.
• Four Jaw Chucks — Besides the number of jaws, the primary distinction between three- and four-jaw chucks is that the latter aren't self-centering, necessitating the separate adjustment of each jaw. This gives these chucks, also known as independent chucks, the ability to successfully hold eccentric or uneven workpieces.
• Magnetic Chucks — These chucks hold the workpiece by employing strong magnetic forces. They can either be permanently magnetic or electromagnetic, and they're suitable for the mass production of thin-sectioned components.
• Collet Chuck — collet chucks are frequently used to hold very small or extraordinarily long workpieces made of bar stock.

Face Plates

Faceplates are used to hold workpieces that can't be supported by chucks or centers. They typically have a circular form with a threaded hole in the center to allow attachment to the lathe spindle's threaded nose. They are used to support bulky, heavy, and asymmetrical workpieces that are inconvenient to hold between centers. Angle plates are used along faceplates to maintain the perpendicular position of the workpiece relative to the lathe tool used.

Driving Plates and Catch Plates

A workpiece held between centers is typically driven using driving plates and catch plates. While both driving and catch plates have a disk form, catch plates contain "U" slots that are intended to accommodate "bent tail" carriers, while driving plates have a driving pin on the face that is used to interact with straight tail carriers.

Carriers

Driving plates are coupled with carriers, also referred to as lathe dogs. A screw is used to firmly fasten the workpiece once it has been placed into the lathe dog's eye. Based on the kind of tail, they can be categorized into two categories:

• Straight Tail — These are coupled with driving plates.
• Bent Tail — These are coupled with catch plates.

Centers

Centers are employed when holding the workpiece between centers. A center's face is conical in shape, while the shank has a Morse taper. These come in two varieties:

• Live Center — Turns with the workpiece.
• Dead Center — Doesn't turn with the workpiece.

Steady Rests

Rests are used to support long, thin workpieces and are typically positioned at the midpoint to prevent the workpiece from deflecting.

Mandrels

Lathe mandrels, also known as lathe arbors, are used to secure holes that were previously bored or drilled into the workpiece, allowing the machining of its outer surface. To allow for effective gripping, mandrels typically have tapered ends that are slightly smaller than their initial diameter.

Summary

If you're interested in learning more about various types of workholding tools and accessories, visit Reid Supply, and refer to their's Engineering Resource Guides.