On the trail we have no grindstones, and often have recourse to a file with which to sharpen our axe; sometimes we use a whetstone for the purpose. New axes are not always as sharp as one would wish; in that case if we use a grindstone to put on an edge we must be sure to keep the grindstone wet in the first place, and in the second place we must be careful not to throw the edge of the blade out of line. When this occurs it will cause a "binding strain" on the blade which tends to stop the force of the blow. If the edges are at all out of line, the probabilities are one will knock a half moon out of the blade in the first attempt to cut frozen timber. The best axe in the world, with an edge badly out of line, cannot stand the strain of a blow on hard frozen wood. While grinding the axe take a sight along the edge every once in a while to see if it is true.