Fig. 897.
Now suppose we have the piece of work shown in [Fig. 897], which requires to have its surfaces a and b parallel and at a right angle to c and d, the end faces e and f parallel to each other, and at a right angle to both a, b, c, and d, the hole at g is to be axially true with the surfaces a, b, c, and d, as well as with the pin at i, and the hole at h at a dead right angle to that at g.
We may put a plug in g and turn up the surfaces e and f, and turn the pin i; this, however, would leave the hole g unbored, whereas it should be bored when the surface e is turned; again, after these surfaces are turned they are of no advantage as guides in the subsequent chuckings.
Fig. 898.
We may grip the surfaces e and f in a jaw chuck to turn the surfaces a, b, c and d, but depending upon the face jaws of the dogs to set the work surface true by; but this would not be apt to produce true work on account of the spring of the jaws, as explained in the remarks upon jaw chucks; furthermore, the work, supposing it to be a foot long, could not be held in a dog chuck sufficiently firmly to enable the turning of the end face e or the pin i, and this brings us to that most excellent adjunct to a general chucking lathe, the angle plate shown in [Fig. 898].
It is simply a plate of the form shown in the figure, having two flat and true surfaces, one at a right angle to the other; one of these surfaces bolts to the chuck plate, while the other is to fasten the work on. The slots shown are to pass the bolts through to fasten the angle plate to the chuck plate, and the work surface of the plate contains similar slots and holes to receive the bolts used to fasten the work.