Material properties are important in tooling because many different materials are employed in tool making. Each material will exhibit very different characteristics in tool life, sharpness, cost, etc. To understand why different materials have such different properties we must first discuss the basic mechanics involved.
Strength is the ability of a material to resist applied external loads. It is this property that keeps a tool from deforming or breaking when stressed. There are many categories of strength.
Flexural strength is the ability of a material to resist loads applied across its longitudinal axis. This is an important property for router tools that are relatively narrow in diameter and often enter the workpiece from the side. (5)
Shear strength is the ability of the material to not break (or shear) in a plane parallel to two forces applied in offset and opposite directions from each other. This is an important mechanical property for tools that will be subjected to significant amounts of torsion. (5)
Tensile strength is the ability of a material to resist two forces that are trying to pull it apart. In brittle materials under bending, tension determines the bending strength. This is important because the cutting edge of many tools is made of brittle materials. (5)
Compressive stresses are basically the opposite of tensile stresses. A material’s compressive strength is its ability to withstand internal rupture due to compression. (5)
Yield strength is the point at which any further stress will cause permanent deformation. That is, the material passes from the elastic zone where it will bounce back to its original shape, to the plastic zone where there is a permanent change in shape. Elasticity is a measure of a material’s ability to deform non-permanently. Plasticity is a measure of a material’s ability to resist stresses in the plastic zone. (5)
Yield strength is important in tooling because we want our tools to be able to stand up to high forces without changing shape. Hardening through heat treatment can increase the yield strength of many metals. (5)