Fig. 44. Cast Elbow held on Angle-plate attached to Faceplate
Application of Angle-plate to Faceplate.—Another example of faceplate work is shown in [Fig. 44]. This is a cast-iron elbow E, the two flanges of which are to be faced true and square with each other. The shape of this casting is such that it would be very difficult to clamp it directly to the faceplate, but it is easily held on an angle-plate P, which is bolted to the faceplate. The two surfaces of this angle-plate are square with each other so that when one flange of the elbow is finished and bolted against the angle-plate, the other will be faced square. When setting up an angle-plate for work of this kind, the distance from its work-holding side to the center of the faceplate is made equal to the distance d between the center of one flange and the face of the other, so that the flange to be faced will run about true when bolted in place. As the angle-plate and work are almost entirely on one side of the faceplate, a weight W is attached to the opposite side for counterbalancing. Very often weights are also needed to counterbalance offset parts that are bolted directly to the faceplate. The necessity of counterbalancing depends somewhat upon the speed to be used for turning. If the surface to be machined is small in diameter so that the lathe can be run quite rapidly, any unbalanced part should always be counterbalanced.
Sometimes it is rather difficult to hold heavy pieces against the vertical surface of the faceplate while applying the clamps, and occasionally the faceplate is removed and placed in a horizontal position on the bench; the work can then be located about right, and after it is clamped, the faceplate is placed on the lathe spindle by the assistance of a crane.
Special faceplate jaws, such as the one shown to the right in [Fig. 33], can often be used to advantage for holding work on large faceplates. Three or four of these jaws are bolted to the faceplate which is converted into a kind of independent chuck. These faceplate jaws are especially useful for holding irregularly shaped parts, as the different jaws can be located in any position.
Fig. 45. Rough Turning a Cylinder Lining—Note Method of Supporting Outer End