I was prompted to write about the issue by several posts where people describe how their axe keeps glancing off the wood instead of biting into it. The answer is simple; the axe is not sharp enough. I can not stress enough how important it is to keep a sharp axe.
Like Abraham Lincoln said: 'Give me six hours to chop down a tree and I will spend the first four sharpening the axe.'
When it comes to axes in particular, there are two reasons why you need to keep it sharp. The first is obvious; sharp things cut better. The second reason is that the geometry of efficient chopping with an axe necessitates that it be kept sharp.
Imagine that there is a tree in front of you. If you swing the axe and hit it perpendicularly from the side, at a ninety-degree angle, the edge of the axe will cut in. If you keep pulling the axe out and swinging it back in the same way, you will spend the rest of the day making cuts into the wood, without much progress.
A much more efficient way to chop wood with an axe is to start by selecting the area where you would like to cut. Then picture a wide V shape with a point ending at least in the middle of the tree trunk. Then begin to cut it from the top and the bottom. The cuts in the pictures here were made with a Cold Steel Trail Boss, the hatchet is used just to illustrate the point.
When a cut is made on the top and the bottom, the material between the two ends of the V should fall off, or can be removed by a slight twist of the axe.
Keep doing that until you reach the point of the V. Then, start on the other side of the tree trunk.
The wider the V, the faster you will remove wood from the tree, and the faster your cut will go.
What does this have to do with your axe being sharp? Well, in order to make a wide V cut, the axe must be very sharp. Because you are coming in at a steep angle towards the wood, if the axe is not sharp, it will not bite into the wood, but will rather glance off. That will force you to narrow the V, bringing the axe blade more perpendicularly to the tree, making the cut a lot less efficient.
How sharp is sharp? Some people like to keep their axes shaving sharp. I do not think that is necessary because that sharpness will go away after the first few cuts. The axe has to be sharp enough however to smoothly cut through a piece of paper, just like you would test a knife.
Few other points:
One, make sure you are using the right axe for the job. If the axe is too small for the size tree you are cutting, it will be much harder to remove the chips of wood between the V cuts, making the job much harder.
Two, if your axe is sharp, but still glances off the wood, you might be using an axe that has too wide of a grind. If the profile of the axe is wide, as it would be on a splitting axe, it will also have a hard time biting into the wood.
Three, the same geometry applies to carving. You very often need to approach the wood at a steep angle, and an axe which is not sharp will glance off rather than cutt into the wood.