Inventors at Work, with Chapters on Discovery

by George Iles

A Beaver Tooth and the Self-Sharpening Plow.

The frames of other animals furnish forth a goodly round of analogies with recent products of mechanical ingenuity. A beaver tooth might well have been the model for a self-sharpening plowshare, widely used throughout the world. This tooth has a thin outer layer of hard enamel, within which, dentine, less hard, makes up the rest of the structure. Gnawing wears the dentine much more than the enamel, so that the tooth takes on a bevel resembling that of the chisel which pays frequent visits to a carpenter’s oil-stone. The scale of enamel gives keenness, the dentine ensures strength, so that the tooth sharpens itself by use, instead of growing dull. Much the same structure is repeated in a plowshare by chilling the underskin of the steel to extreme hardness, while the upper face of the share is left comparatively soft. As it goes through the ground the upper face wears away so as to yield a constantly sharpened edge of the thin chilled under metal. Thus the heavy draft of a dull share is avoided without constant recourse to the blacksmith for re-sharpening.

Beaver teeth.