Fig. 1949.
Thus, in [Fig. 1949] is shown a sectional view of a gang of three mills or cutters, a, b, and c, of which a and c are recessed to admit of the ends of b passing within them. The heavy black line representing a paper washer inserted to adjust the distance apart of a and c, it being obvious that this gives a means of letting them together after their side teeth at d and e have been ground. As shown in the figure, a has teeth on one only of its sides, while c has them on both sides as well as in its circumference, while all three are of different widths of face. This would capacitate a only for the inside cutter, as in the figure, while b would be serviceable only when there was a cutter on each side of it; or if used singly, only when its face overlapped the width of the work on each side. But c, being cut on each side, could be used singly for grooving or recessing, or for plain milling, or in the position of b or a in the figure; hence it is preferable in gang milling for general purposes to provide teeth on both sides as well as on the circumference of the mill or cutter. But if a gang of mills are to be made for some special purpose, and used for no other, the teeth may be provided on the sides or not, as the circumstances may require.
Fig. 1950.
Fig. 1951.
Suppose, for example, that steps, such as shown in [Fig. 1950], were required to be cut in a piece of brass work, and that, the work requiring to be very true, a set of roughing and one of finishing cutters be used, then the latter may be put together as in [Fig. 1951], there being eight separate cutters, and their ends being slightly recessed but without teeth. Such cutters would wear a long time and may be readily sharpened, and there being no side teeth, the widths of the cutters, individually and collectively, would not be altered by the grinding; hence no readjustment with washers would be necessary. The tooth corners must, however, be kept sharp, for in proportion as they get dull or blunt, the sides of the cutter wedge in the work, causing friction and extra power to drive them as well as producing inferior work.