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Meaning of underdraft

un•der•draft

Pronunciation: (un'dur-draft", -dräft"), [key]
— n. Metalworking.
  1. a tendency of a rolled piece to curve downward after passing through a stand, occurring when the upper roll is faster than the lower. Cf.(def. 7).
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.