While production flow does stop if the machine jams, the delay is short and well compensated by the improved grade yield which results from a direct mechanical measurement. One of the properties which dramatically affects the performance of a piece of lumber is the grain angle relative to the long axis of the piece. This is a difficult and imprecise task at best. We are not aware of any mechanical production-line lumber grading equipment in which a shear force is applied. Almost all of these machines apply a bending force.
Shear stress is induced as a result.
A few apply a tensile force. A few very-low speed machines measure deflections with constant applied force, but the major producing machines apply a constant bending deflection and the bending force is measured. There is an important distinction here. These statements leave an incorrect impression. First, some pieces are broken in the planer as it forces warped lumber into a straight line.