Making small gauge-rings about an inch or two inches in diameter is performed by boring holes into well-forged cakes of steel while attached to a lathe-chuck. The chuck is a dog-chuck or grip-chuck, consisting of a disc-chuck having a pair of angular grips connected with one screw. This screw is a spindle on one half of which is a right-hand screw for working one of the grips, and having on the other half a left-hand screw for moving the other grip; such a screw is fitted to the disc-chuck, and rotated for fixing and unfixing the work by means of a spanner which fits both ends of the screw. Such a screw by being rotated will move both the dogs in • opposite directions at the same time, so that when a piece of work is between the dogs, it is fixed or unfixed by merely placing the spanner to only one end of the screw and rotating it. Chucks worked with right and left screws, are of several sizes, and have dogs of various shapes. One class of these are denoted in Fig. 540, in which a right and left-screw chuck is shown, that is suitable for boring gauge-rings and a large number of rings for other purposes. When used for gauge-rings, each ring is first bored while in the chuck to a diameter which is smaller than the finished diameter; they are next turned on an arbor in some other lathe to reduce them to the proper thickness and outer diameter ; after this they are again fixed to the same lathe-chuck, or to some other lathe, and the holes are finally bored with a slide-rest tool and water.

The turning of gauge-rings about four or six inches in diameter is performed in a manner somewhat resembling that for smaller ones; and if to be hardened, it is done next to the first boring and turning of the entire surfaces. After being softened for the second turning, the outer sides are finished while on an arbor; consequently, while fixing each ring to the chuck to be finally bored, the outside of the ring is made to rotate exactly concentric with the lathe-spindle or with the outer edge of the chuck. This concentricity is termed truth ; and when a certain edge, rim, side, or other portion of a piece of work rotates concentric with the lathe-spindle, the particular edge or rim runs truly. If a right and left-screw chuck is used for boring large rings, a couple of fastening-plates and bolts are required to hold the work, in addition to the two dogs. While thus held, the hole is finally bored with a slide-rest tool, and also, in some cases, finally ground to the finished diameter while still in the dogs.

In order to avoid much of the lathe-boring with slide-rest tools, it is proper to enlarge the holes in the rings by means of a drilling-machine when a large quantity of metal is to be taken out. The drill used for this purpose is usually a cylindrical one having a few cutting teeth at the end; such a drill is termed a rosebit, and is represented by Fig. 517. This tool is specially adapted to vertical drilling-machines, but is also sometimes used in a lathe, to avoid taking out several cuts from a ring or boss, and also to roughly adjust a number of holes to one diameter without the need of measuring. A rosebit in use in a lathe is shown in Fig. 540, being 'supported at one end with the poppet-pivot. A rosebit is not used until the hole is truly bored by some other means; and when a proper quantity has been taken out, the rosebit is used to avoid boring with a slide-rest tool, or to finish the hole to the diameter desired. If a rosebit is employed to bore a steel gauge-ring, a plentiful supply of oil is given to the tool while the work rotates ; the oil at such times is poured into one of the oil-channels of the rosebit, by which means the oil travels to the cutting teeth of the tool. During the rotation of the work, the rosebit is held by a spanner which fits the square head of the tool next to the poppet-pivot. In the Figure the long end of the spanner is shown in contact with the carriage, and to advance the tool into the work the operator rotates the poppet-wheel, which advances the poppet-cylinder, and, consequently, the rosebit in contact.