More uses for wedges What about wedge angle?

An axe is a good example of a wedge, as is any cutting or chopping edge, such as a knife, a chisel, a pin or a nail. In these cases and in all wedges, there are two or more inclined planes tapering to an edge or a point.

When using an axe the sharp edge penetrates the surface of a log of wood, then the sides of the wedge split it apart by applying a large sideways force. Friction reduces the efficiency of a wedge so sometimes extra force has to be applied by a heavy hammer.

A blow with a hammer forces the point of a nail into wood. If you examine the point of a nail carefully you will see that it is really four wedges, enabling it to pierce wood easily, then push the fibres apart. This last action increases friction between the wood and the nail, holding the nail firmly in place. Sometimes a nail splits the wood when the sideways force is more than the wood grain can withstand. A pre-drilled hole helps prevent this from happening.

More uses for wedges
Other examples of wedges in action are scissors slicing through paper and pushing the separated halves apart, a chisel slicing a thin layer from wood, and a guillotine slicing through paper or metal.

A wedge can be used to keep a door open. Friction holds the wedge to the floor and the door is prevented from rising further up the wedge by its hinges. This is a simple application of the wedge and the reverse can apply. By tapping a wedge into a gap a heavy object can be raised and secured.

Door wedge.

What about wedge angle?
The wedge of a sharp knife has a very small angle between the sides of the wedge. This means that it can cut easily but is not very good at splitting. An axe has a larger angle between the wedges and can cut and split wood fairly effectively. A blockbuster on the other hand has a high wedge angle so is not good for cutting but excellent for splitting logs for example where there is already a fine split.

Sometimes a combination of angles is used, for example in a chisel. The first wedge has an angle for cutting, then the angle changes to push the shaving away from the work.

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