What is the purpose of a three-jaw chuck on a drill press or lathe?

• A. To hold round stock securely in true alignment
• B. To measure diameters accurately
• C. To drill holes in precise locations
• D. To support cutting fluids

Answer: (A)

The three-jaw chuck is a self-centering gripping device. Its three jaws are linked to a single scroll so when you tighten or loosen it, all jaws move together, drawing the workpiece into the middle of the chuck. This centers round stock precisely with the spindle axis, giving true alignment for turning or drilling along a straight path. It’s especially handy because setup is quick and repeatable for round pieces. It’s not suited for square or irregular shapes, since the jaws are geared to center round stock. It also isn’t used for measuring diameters or for applying cutting fluids—the chuck’s job is simply to hold the work securely in line with the spindle.