[Fig. 892] represents a view of the end l as held for the second chucking. c is a section of the chuck plate, and o o represents the line of centres of the lathe, and it is obvious that the radial face of the lever end (which is here represented by l) being used for all but the first chucking, the holes will all stand axially true one with the other, no matter how many chuckings and holes there may be, hence it becomes obvious that the face that will meet the chuck plate is the one that should be turned at the first chucking. It is of no consequence in the case of a single lever whether the pin fits the hole in the end of l, [Fig. 892], or not, because the dotted circles at b, c, d in [Fig. 891] form the guides whereby to set the holes for distance apart, and any bolt may be used to clamp the work.
It is usual in an example of this kind to turn the stem of the lever to its proper thickness for a short distance from the hubs, so as to have the stem true with the bores, and form a guide whereby to set the lever in the planer or shaper when cutting down the lever stem to size. The rules of chucking and the balance weighting described with reference to chucking a crank, of course also apply to this example.
It will now be observed that in all cases in which work is chucked by bolts and plates, the whole of the faces cannot be turned at one chucking unless the shape of the work is such that it will permit the plates and the bolts to pass or be below the level of the work surface. It will further be noticed that if one face of the work is held against the chuck surface it cannot be turned at the same chucking that the other face is turned at. Now it may be very desirable that a part or the whole of the back face as well as the front one be turned at the same chucking as that at which the hole is bored, so as to have the hole and those two faces true without incurring the errors that might arise from a second chucking. Again, the diameter of the work may be equal to that of the chuck so as to preclude the possibility of using bolts and plates outside of the circumference, and though there be cavities or slots running through the work through which the bolts might be passed, yet the presence of the plates would prevent the face from being turned.
Fig. 893.
To meet these and many other requirements that might be named, chucking by the aid of chucking dogs is resorted to, one of these dogs being shown in [Fig. 893]. b represents a section of the chuck plate with a piece broken out to show the stem a of the dog, which is squared to prevent its revolving when the nut d, which holds the dog to the chuck plate, is tightened, the holes of the chuck, of course, being square also; e is the set-screw which holds the work, its end at e being turned down below the thread, and the head squared to receive a wrench.
Fig. 894.