The Collaborative International Dictionary of English v.0.48:

Doffer \Doff"er\, n.
   1. (Mach.) A revolving cylinder, or a vibrating bar, with
      teeth, in a carding machine, which doffs, or strips off,
      the fiber from the cards.
      [Webster 1913 Suppl.]

   2. (Spinning) A worker who replaces full bobbins by empty
      ones on the throstle or ring frames.
      [Webster 1913 Suppl.]