Figure 9-11.—60-degree lathe centers.Figure 9-12.—Lathe dogs.Lathe CentersThe 60-degree lathe centers shown in figure 9-11provide a way to hold the work so it can be turnedaccurately on its axis. The headstock spindle center iscalled the LIVE CENTER because it revolves with thework. The tailstock center is called the DEADCENTER because it does not turn. Both live and deadcenters have shanks turned to a Morse taper to fit thetapered holes in the spindles; both have points finishedto an angle of 60°. They differ only in that the deadcenter is hardened and tempered to resist the wearingeffect of the work revolving on it. The live centerrevolves with the work and is usually left soft. The deadcenter and live center must NEVER be interchanged.(There is a groove around the hardened dead center todistinguish it from the live center.)The centers fit snugly in the tapered holes of theheadstock and tailstock spindles. If chips, dirt, or burrsprevent a perfect fit in the spindles, the centers will notrun true.To remove the headstock center, insert a brass rodthrough the spindle hole and tap the center to jar it loose;then pull it out with your hand. To remove the tailstockcenter, run the spindle back as far as it will go by turningthe handwheel to the left. When the end of the tailstockFigure 9-13.—Center rest.screw bumps the back of the center, it will force thecenter out of the tapered hole.Lathe DogsLathe dogs are used with a driving plate or faceplateto drive work being machined on centers; the frictionalcontact alone between the live center and the work is notsufficient to drive the workThe common lathe dog, shown at the left in figure9-12, is used for round work or work having a regularsection (square, hexagon, octagon). The piece to beturned is held firmly in the hole (A) by the setscrew (B).The bent tail (C) projects through a slot or hole in thedriving plate or faceplate so that when the tail revolveswith the spindle it turns the work with it. The clamp dog,illustrated at the right in figure 9-12, may be used forrectangular or irregularly shaped work. Such work isclamped between the jaws,Center RestThe center rest, also called the steady rest, is usedfor the following purposes:1. To provide an intermediate support for longslender bars or shafts being machined between centers.The center rest prevents them from springing, orsagging, as a result of their otherwise unsupportedweight.9-8
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