The tailstock assembly is composed of the main casting, a spindle (or ram), a spindle-locking lever, a hand wheel, and a mechanism to secure the unit to the lathe bed. Whereas the headstock is stationary, the tailstock can slide along the bed to accommodate work of varying lengths and can be locked at the desired distance from the headstock.
The advantages of a good tailstock should not be overlooked because it does much more than just hold a center. As with the headstock spindle, the tailstock spindle should be machined to accept Morse-taper accessories. Look for a spindle equipped with a #1 , #Z, or #3 Morse taper. The tailstock spindle sometimes runs a bit smaller than the headstock spindle. For example, if the headstock spindle is 1 1/2 in. dia., the tailstock spindle is typically 1 in.
An important aspect of tailstock design is spindle travel-the amount the spindle can be moved when the tailstock is locked to the bed. Lathes typically have about 2 1/2 in. of spindle travel, which is adequate for most applications. I prefer to work with a tailstock spindle that can move as much as possible because the tailstock itself doesn’t have to be moved as often.
The tailstock spindle is advanced and withdrawn by turning a handwheel, which is no more than a large nut. A lever on top of the tailstock locks the spindle in place and prevents it from drifting due to the vibration caused by turning. The traditional tailstock setup calls for the outside of the spindle to be left-hand threaded (see the photo on p. 2 1). Because the thread is left-handed, the spindle advances when the handwheel is turned clockwise, which is normal to our way of thinking. This design is typically used on cheaper lathes, although it is sometimes also found on very expensive ones. Accessories are ejected by inserting a knockout bar through the spindle.
A more elegant arrangement is a self-ejecting spindle. The inside of the spindle is left-hand threaded, and a long left-hand screw extends from the hand wheel into it (see the photo below). Turning the wheel to the right advances the spindle, while turning it left withdraws it. As the spindle is retracted all the way rearward, the screw bumps the Morse taper in the spindle and ejects it. A crank handle is often added to the handwheel so that the spindle can be moved quickly.
The tailstock must lock securely to the bed and not move while you’re turning. There is a variety of locking mechanisms, ranging from a stud running down between the bed rails with a plate and a nut to complicated cams. The main thing to look for is a good positive lock that will hold the tailstock without its drifting backward when you apply pressure to the work with the hand wheel.