Fig. 1737.
[Fig. 1736] represents a common form of cotter or keyway drill, the cutting edges being at a, a, and clearance being given by grinding the curve as denoted by the line c. In some cases a stock s and two detachable bits or cutters c, c, are used as in [Fig. 1737], the bits being simple tools secured in slots in the stock by set-screws, and thus being adjustable for width so that they may be used to cut keyways of different widths.
Fig. 1738.
The feed of keyway drills should be light, and especial care must be taken where two spindles are used, to keep them in line, or otherwise the keyway will not come fair, as is shown in [Fig. 1738], where the half drilled from side a and that drilled from side b are shown not to come fair at their point of junction c. This is more apt to occur when a deep keyway is drilled one half from each side. Hence in such a case great care must be exercised in setting the work true, because the labor in filing out such a keyway is both tedious and expensive.
