The Collaborative International Dictionary of English v.0.48:

Rock shaft \Rock" shaft`\ [Cf. Rock, v. i.] (Mach.)
   A shaft that oscillates on its journals, instead of
   revolving, -- usually carrying levers by means of which it
   receives and communicates reciprocating motion, as in the
   valve gear of some steam engines; -- called also rocker,
   rocking shaft, and way shaft.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Rocking \Rock"ing\, a.
   Having a swaying, rolling, or back-and-forth movement; used
   for rocking.
   [1913 Webster]

   Rocking shaft. (Mach.) See Rock shaft.
      [1913 Webster]