Physics-exploiting axe splits wood in record time

Interesting Engineering

A new axe design has taken full advantage of known physics to chop the time it takes to split up a log of wood. Finnish inventor Heikki Kärnä is the man behind the Vipukirves Leveraxe and his aim was to redesign the axe using simple principles of physics to make it more efficient and safer.

Vipukirves-590x330[Image Source: Heikki Kärnä/ LeverAxe]

This 1.9kg is more than a unique personal item, they are actually for sale but they do come at a price - €193.12. So what is it about this axe that would convince you to spend the little extra over a traditional design.

A traditional axe is a simple wedge of metal on a handle that passes momentum on to the wood when it is struck; if there is enough momentum, the wood splits. Its a pretty direct force and optimisation of design comes in finding the perfect wedge shape to penetrate the wood to pass on the swinging momentum.

The Leveraxe however acts more like a lever. The centre of gravity is shifted from the centre-line by placing the wedge offset to the handle. When the wedge of the axe penetrates the wood, the remainder of the kinetic energy provide rotation around the centre of gravity and the axe acts more like a lever - as you may have guessed from the name. A single strike is said to be enough to open the wood by up to 8cm, ample enough to split it.

The design means that less force is required to do the same amount of splitting. The kinetic energy used in the rotation would either by wasted and transferred to the user or used less efficiently in passing on direct momentum. This wasted energy in traditional axes is said to cause harm through abrupt shock and deflection.

Vipukirves_x_jpg-590x391[Image Source: Heikki Kärnä/ LeverAxe]

"Everybody who has tried splitting wood with a traditional axe knows that it takes a lot of power to penetrate and split the wood," according to the axe-maker, but with the Leveraxe, "You can easily and safely start splitting suitably sized logs from the sides by striking closer to edges. No more needing the futile first heavy strikes just to get the log split in two."

Another feature is that due to the final lever motion of the axe it doesnt becomed wedged in to the wood if it doesn't split, meaning it is always easy to retract the axe and continure striking,

"When using a chopping block with a tire setup you can achieve a burst of strikes at a frequency of 100 strikes a minute. Thus, as an example, using 10 strikes to chop a log would take 6 seconds," Kärnä said. Check out the slow-motion video below to see it in action: