The turbine shaft comes out of the chimney here. You can see from the colour of the metal that it is made of brass. The brass bevel gears take the energy across the front of the fireplace to the pulleys.

Brass is an alloy of copper and zinc. It is very hard. This is because it needs to stand up to a lot of rubbing by the other gear. This complicated shape would have been made by heating the brass so that it melted and then puring it into a sand mould. Try pushing a button into some plasticene - the shape it makes is a mould for the button.

More information about bevel gears...