Fig. 1734.
Another tool for taking a very light cut to smooth out a hole and cut it to exact size is the shell reamer shown in [Fig. 1734], which fits on a taper mandrel through which passes a square key fitting into the square slot shown in the shell reamer.
Fig. 1735.
Reamers may be driven by drill chucks, but when very true and parallel work is required, and the holes are made true before using the reamer, it is preferable to drive them by a socket that permits of their moving laterally. Especially is this the case with rose-bits. [Fig. 1735], which is taken from The American Machinist, represents a socket of this kind, being pivoted at its driving or shank end, and supported at the other by two small spiral springs. The effect is that if the socket does not run quite true the reamer is permitted to adjust itself straight and true in the hole being reamed, instead of rubbing and binding against its walls, which would tend to enlarge its mouth and therefore impair its parallelism.
Cotter drills, slotting drills, or keyway drills, three names designating the same tool, are employed to cut out keyways, mortises, or slots.
Fig. 1736.