VI. The action of cutting tools

The action of cutting tools has not often been treated from a theoretical point of view; in fact I only know of two papers on the subject, one by Professor Willis and the other by Mr. Babbage. Of these Professor Willis’s paper is purely geometrical, showing what angles the edges of tools may make with one another if the cutting angles are to be such as experience shows to answer best. Mr. Babbage, on the other hand, does not enter at all on the question of the shape of the tool, but by making certain assumptions as to the relation between the dimension of the shaving removed by a tool and the work required to remove it, he deduces some results showing how to remove a given amount of material most economically. His conclusions cannot be considered correct, nor do they agree with experience (see Note 1). I do not attempt in the following paper to give any dynamical investigation of the action of tools, in fact it would be almost impossible to do so without a more extended knowledge of the laws which govern the strains in bodies subjected to large forces, but merely to classify the various actions which observation shows to be caused by the progress of the tool, and to quantify approximately the work expended in each. For this purpose, shavings from a great variety of substances were examined both in the course of their formation (by a microscope attached to the toolholder) and after they were removed. Among the substances examined may be mentioned four or five samples of wrought iron, and as many of steel, cast iron, gun metal, brass, copper, lead, zinc, hard paraffin, soap, and clay.