Toolholder

While the insecure holding of the bit in the toolholder is a factor in tool breakage, it is far from being the only factor; there are many other factors — the quality of the carbide, the material being machined, the type of machine being used […]

In cases without good face contact, the diameter of the toolholder at the front of the flange or the tool itself should not be any larger than the gage diameter of the toolholder shank from a bending stiffness viewpoint.