A method of determining characteristics of a rotary drag-type drill bit

A method is disclosed for determining the characteristics of a rotary drag-type drill bit. The method comprises the steps of creating a model or representation of the shapes of the cutter (12) and their positions relative to an axis of the bit, projecting the shape of one of the cutters (20) onto a fixed plane (21), overlaying the plane (21) with an array (24) of cells and assigning a first marker to those cells which overlie the projection (23). The model is then rotated, conveniently in the reverse direction, and moved axially. As each of the cutters (12) move through the plane (21), their shapes are projected onto the plane (21), and those cells which overlie both the projection of the selected cutter (20) and the projections of one or more of the the other cutters (12) are assigned a second marker. One or more parameters are derived using the markers applied to the cells of the array (24).