When sawn timber is planed, the timber is to some extent flattened by the feeding rollers and other pressure elements inside the planer, with the plank middle affected to a greater degree than the top and butt end. As a result, any twist present in rough timber influences the planing process in the proximity of the latter two areas. This is manifested primarily as reduced rectangularity in the affected zones of the planed timber, but also as an increased risk of planer misses. One way to avoid these unwanted features in the end product is to plane an excess length of timber, then cross-cutting to the required final length after planing.This study found low rectangularity to be a larger problem than planer misses, with the top end most affected. The study also indicates that simple models could be used to predict the size of the zone affected by twisting near the ends of planed timber, and thus also the length that must be removed in order to produce an acceptable cross-sectional shape throughout the length of planed timber.