The wedge follows the grain of the wood, but the edge tool can follow a line determined by the worker.

The edge is a refinement and improvement upon the wedge and enables the worker to be somewhat independent of the natural grain of the wood.
In general, it may be said that the function of all cutting tools is to separate one portion of material from another along a definite path.

All such tools act, first, by the keen edge dividing the material into two parts; second, by the wedge or the blade forcing these two portions apart.

If a true continuous cut is to be made, both of these actions must occur together.

The edge must be sharp enough to enter between the small particles of material, cutting without bruising them, and the blade of the tool must constantly force apart the two portions in order that the cutting action of the edge may continue.
The action of an ax in splitting wood is not a true cut, for only the second process is taking place, Fig.59.The split which opens in front of the cutting edge anticipates its cutting and therefore the surfaces of the opening are rough and torn.
[Illustration: Fig.59.Wedge Action.] [Illustration: Fig.60.Edge Action.] When a knife or chisel is pressed into a piece of wood at right angles to the grain, and at some distance from the end of the wood, as in Fig.