Abstract: An improved reciprocating knife includes a blade with a blade opening, a blade guide defining a track for guiding the blade reciprocation, a blade drive having a rotating drive shaft and an angled cam plate which extends into the blade opening, means for mounting the blade drive such that rotation of the drive shaft causes the cam plate to engage the rim of the blade opening to reciprocate the blade, and biasing means for biasing the rim of the blade opening against the cam plate to modulate the play between the cam plate and the rim. The biasing means is designed to aid blade reciprocation over a portion of the reciprocating cycle and to resist blade reciprocation over another portion of the reciprocating cycle. Reinforcing for the rim of the blade opening, a replaceable blade cutting edge section, and a collar for adjusting the fit of the drive shaft in the knife are also disclosed.