Two Types of Undercut Paper Stretching or Warpage Straightening
When the cut side of the paper bundle is checked after cutting, occasionally the top few sheets are longer than the setting size. This phenomenon is generally called 'undercut.' There are two types, each with a different cause.
First, stretching of the paper at the moment of cutting (see figure). At the moment the knife comes down and the edge touches the paper on top, a few sheets are stretched by the pressure of the knife. The lower sheets are cut exactly according to the setting because they do not stretch due to pressure.
The second type of undercut is the phenomenon of the top few sheets slipping a little toward the back gauge due to the pressure of clamping. This slippage is due to warpage caused by insufficient air release or warped paper. The knife comes down and the paper is cut; when the clamp is raised and the force is dispersed, the warpage is straightened, causing inaccuracy. To deal with undercut, first look closely at the side that was cut.