Shop Operations: Catch a tiger by the tail

In the finest Yankee tradition, American job shops develop creative tooling and workholding solutions to keep the wheels of industry turning and get work out the door when the need arises. There is one such operation that is common enough—and tricky enough if not handled properly—that most experienced machinists have at least one exciting story to tell.

Most folks who run an engine lathe often work on the ends of long shafts, or rods, that protrude unsupported out of the headstock. Depending on the shaft diameter and how much unsupported length sticks out, this operation can be dangerous because of the high potential for shaft whip. However, with the proper tooling, this operation is a cinch to perform safely.

An unsupported shaft protruding from the headstock can be dangerous. Images courtesy of T. Lipton.

As the unsupported, protruding shaft rotates, it tends to oscillate. Unchecked, the shaft can start to whip. As the speed increases, this whipping can become self-reinforcing and cause the shaft to bend, destroying anything in its path as it spins like a windmill.

Best practice is to have no part of a shaft protruding unsupported from the headstock. However, this is not always possible, because job shops are called on to make whatever custom parts stumble through the door. Fortunately, there are good ways to greatly reduce—or even eliminate—the risk.

For small, quick jobs, insert a cork that’s bored to fit the workpiece diameter into the open spindle bore to support the shaft as it exits the headstock. This cheap and easy solution is for shafts that slightly protrude from the headstock. It’s a simple idea for supporting shafts smaller than the ID of the spindle on the center of rotation.

Inserting a cork in the spindle bore is one way to work with slightly protruding shafts.

Another useful support accessory is a small chuck, which can be adapted to fit the rear of the headstock. This approach is suitable for a range of diameters, and you can accurately center the chuck to the spindle’s rotational axis. This detail is important for deep-hole drilling in the ends of a shaft or for features that need to be very accurately machined, relative to the shaft axis.