Page:Practical Treatise on Milling and Milling Machines.djvu/78

72 variety of work is encountered. It is found of advantage for holding irregular or angular pieces and forms, also in determining and forming the edges for model parts of machines and work of a similar class. Often this vise will take the palce of an expensive fixture. It can be set at any angle and the work placed in position or removed

without disturbing the setting. It can also be easily removed form one machine to another and several operations performed without removing the piece of work. The base is double, and is fastened to the table by bolts that fit into the table T slots. It has two sets of bolt slots to allow for moving the vise back when set in a vertical plane. The upper part is a hinged knee, that swivels on the lower part of the base, and it can be set at any angle in a horizontal plane, graduations to degrees indicating the position. The top section of the knee is hinged to the lower part in such a manner that it can be set at any angle to 90° in a vertical plane, and clamped rigidly in position by the nut on the end of the bolt forming the hinge and by the bolt at the joint in the bracing levers. Graduations on a steel dial at the side of the vise indicate the elevation of the knee. A swiveling movement is also provided for the vise proper on the upper part of the hinged knee, and it can be set and clamped at any angle to the axis of the bolt forming the hinge.

Index Centres. These mechanisms are employed for obtaining exact spacing of more common numbers of divisions upon the periphery of pieces of work, such as in cutting the teeth of small gears, ratchets and cutters, fluting taps and reamers, milling the sides of nuts and heads of bolts, and various other purposes. They are used principally upon machines not fitted with a spiral head, for their functions in most instances can be equally well performed by the latter, which also offers many additional advantages.

Like otehr attachments, their efficiency is largely dependent upon their design, and it is important that they be exceedingly stiff,