Defining chucks used for turning

For turning applications, there are many types of workholders. One is the chuck, a universal holding device capable of OD or ID clamping. It can be manually, pneumatically, hydraulically or electrically actuated.

Lathe chucks are mounted horizontally, vertically (facing up) or inverted (facing down). The chuck is bolted to a machine-mounted adapter plate. A drawtube is connected from the rear of the chuck, and the CNC or operator actuates the drawtube to clamp and unclamp the chuck.

Figures 1 and 2. A 3-jaw OD chuck (top), and a 3-jaw ID chuck.

Workholding components, sometimes called top tooling, are mounted to the chuck face. (Top tooling components are sometimes, but not always, jaws.) The workpiece is placed in the center of the tooling, the drawbar is actuated and the part is clamped in a defined manner based on the type of chuck being used.

The jaws (or another type of top tooling) slide to and from the chuck centerline. There can be two to eight jaws, depending on part shape, configuration and clamping area available. Figure 1 is a typical 3-jaw OD chuck.

When using a 3-jaw ID chuck (Figure 2), the part ID may or may not have been machined prior to setup. All chucking operations require a specifically designed process, because to function correctly the jaw diameter must closely match the part diameter.

Figure 3 shows a part being held between centers that was previously machined on the ends. This allows the part to be completely turned in a single operation, which is common for finish turning and hard turning applications, such as turning shafts with tight tolerances from end to end. Turning between centers with face drivers requires a chuck, a driver mounted in the chuck and an opposing center for stability.

Figure 3. A part being held between centers.

As with most workholders, specific chucking solutions for unique cutting requirements are custom-designed. For example, Jade Tool Inc., Traverse City, Mich., has been designing and building custom chucks for more than 20 years. Among other products, the company has developed pin chucks for roughing and finishing. The following examples are custom chucks designed by Jade Tool.

A pin chuck (Figure 4) pulls the part against the stop face (end stop) and has jaws that rock side to side to ensure secure six-point contact on the part, even if it is out of round.

Figure 4. A pin chuck.