Engine Lathe Operations and Controls - 11: Centers, Dogs, and Faceplate
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WARNING: Machine tools present a safety hazard. Improper operation can result in severe injury. These topics are for non-laboratory study only and are not to be used in conjunction with the operation of any tool or machine described herein. Never use a machine tool without the supervision of a qualified instructor.
To hold a work piece directly in the center of the spindle and be true to (in line with) the spindle a center can be used. There are three types of centers; the live center (figure 1), the dead center (figure 2), and the half center (discussed below). A live center rotates on internal bearings. A dead center does not rotate. A dead center creates friction and must be lubricated (the live center rotates with the part and does not create friction). All centers are 60 degrees at the tip. To assure that the center is holding the work piece correctly, a special hole is center drilled at the end of the work piece that matches the shape of the center. Faceplates (figure 3) are also called Driver Plates. They are circular with a slot or a series of slots for bolts or to hold the bent-tail of a lathe dog (figure 4). To turn a shaft that is being held by centers a dog is used with a faceplate. Faceplates are also available with T-slots for clamping.
Figure 1
Figure 2
Figure 3
Figure 4
Special circumstances require special tools. The half center is just such a tool. It is used to provide special clearance for lathe tooling. With this setup you can see how the live center in the tail stock interferes with the tool bit. With the half center installed the tool bit has clearance. Half centers are always dead centers. Remember to keep them greased as they do not turn freely like a live center.
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