1、Headstock of Engine Lathe The headstock assembly is permanently fastened to the left end of the lathe. It contains the headstock spindle, which is rotated by gears or by a combination of gear and pulleys. The spindle holds the attachments which, in turn, hold and turn the workpiece. Spindles come in
2、 several quality ratings and are supported in headstocks by three to five bearings. Since the accuracy of the work done on a lathe depends on the axis of rotation of the spindle holding the workpiece, the spindle and all its accessories must be built and assemble with the greatest possible care. A h
3、old extends through the spindle itself. The front end of this hole is tapered for holding tools having a tapered shank. A taper sleeve (a hollow-round part) fits into the taper spindle hole, when holding a headstock, or live center. The headstock center is called a live center because it turns with
4、the work. The center is a tapered metal part with a pointed end. It is used to support the end of a workpiece as it is being turned. All lathe center point have a 60-degree() included angle. Three common types of spindle noses are used to hold attachments on the spindle. 1. The threaded spindle nose
5、 has been used on lathes longer than any of the other types. Attachments to be mounted are screwed onto the spindle until they fit firmly against the spindle flange. The major disadvantage of the threaded spindle nose is that turning cannot be done in the reverse position (with the spindle turning c
6、lockwise). This is Because certain attachments, a chuck for example, would come loose. 2. The cam lock spindle nose has a very short taper which fits into a tapered recess in the back of a faceplate or chuck. A series of cam lock studs projects from the back of the faceplate or chuck. These cam lock
7、 studs fit into the hole in the spindle nose. They are locked into position by turning a series of cams. 3. The long (steep) taper key drive spindle nose has a long taper with a key attached and an internal threaded collar. The faceplate or chuck must have an equal taper and keyway plus an external
8、thread. This positive lock-type of spindle is most popular on medionum-size lathes. It permits cutting with the spindle turning in either direction. Power for driving the spindle is provided by an electric motor. There are four common ways of transmitting the power form the electric motor to the spi
9、ndle. These include: Flat belt drive. On most belt-driven lathes, direct drive power is delivered through belts to a step pulley attached to the spindle. The spindle speed is changed by moving the belt to different positions on the step pulley. To obtain slower speeds and more powder, back gears are
10、 used. To understand how the back gears operate, study Fig, 2-3 Notice that gear F is fastened securely to the spindle. This gear is often called a bull gear. The small end of the step pulley gas a small gear attached to it called a pinion gear. This gear (E) always turns when the pulley turns. The
11、step pulley and pinion gear are connected with the bull gear by a sliding pin called the bull-gear lock-pir. At the back of the headstock are two gears mounted on the same shaft. They are spaced to line up or mesh with the bull gear (F) and pinion gear (E). These are called back gears. To engage the
12、 back gear, the pin in the bull gear is pulled out (when the pin is out, the pulley and pinion gear will turn, but the spindle will not turn). Pull the back gear handle forward to mesh the back gears with bull gear F and pinion gear E. Do this by turning the step pulley by hand-never while the power
13、 is on. When engaged, power is delivered directly to the bull gear (F) and spindle by the back gears. At the left end of the headstock assembly is a feed reverse lever. It is used for reversing, the direction or movement of the lead screw. This lever can be moved to three positions. When it is in th
14、e upper position with the automatic feed engaged, the carriage will move to-ward the headstock (to the left) and the cross-feed will move in. When in the center position, the gears are out of mesh and the lead screw will not move. When in the lower position with the automatic feed engaged, the carri
15、age will move toward the tailstock (to the right) and the cross-feed will move out. V-belt drive. A V-shaped groove is cut around the circumference of each pulley, and a V belt fits accurately into this groove. The V belt does not touch the bottom of the pulley. This type of drive has a back gear ar
16、rangement similar to that used on flat belt machines. Variable-speed driver. In this arrangement it is possible to change the speed between the driver and driven pulleys without stopping the lathe. In fact, the speed must be changed only when the machine is running. The driving pulley of a variable-
17、speed drive is made with parts having V-shaped sides. One side of the pulley may be opened or spread apart from the other side. As it spreads apart, the belt moves inward toward the smaller diameter, producing a slower speed on the driven pulley. As the sides of the pulley are brought together, the
18、belt is forced outward toward the large diameter which increases the speed of the driven pulley. The speed change may be done either manually or hydraulically. On the hydraulic type, a control dial located on the top of the head stock accurately activates the hydraulic system. Do not turn the contro
19、l dial unless the motor is running. Speeds are from 300 to 1,600 revolutions per minute (rpm) in direct drive. For slower speeds, the lathe must be stopped and the back gear knob moved. This will provide slower speeds of 43 to 230 rpm. 4. Geared head. This headstock contains gears and changing mechanisms for obtaining many different spindle speeds. The speed index plate attached to the headstock will help the operator select the required speed. Two or three levers or knobs must be moved to adjust the speed.
