A hammer having a face in the shape of a thin rectangle is assumed to produce a plane-strain indentation. By applying rings of blows to a thin disc with the hammer face oriented circum-ferentially or radially, various axi-symmetric distributions of internal stress may be set up. Theoretical stresses were used for calculating changes in stiffness in various harmonic modes of flexure. Hence, effects of distributions of the two types of blow were assessed. The theoretical results, confirmed by controlled experiments, serve to elucidate some aspects of workshop practice.