Page 305 - The Lost Ways

on the left and a lantern gear on the right). To allow the axles to cross, the gears would
actually mesh slightly off center, as shown in the left diagram.

The vertical axle would pass through the floor of the mill and into the second story, where
the milling operation would occur, regardless of the type of milling to be done.

However, gears do more than change direction; they also change speed and power. Water
wheels don’t operate very quickly, so it is useful to speed up their operation in order to
make the milling operation go faster. This is why

different sized gears are used in the gear train.

In this diagram, we see two different sized gears:
gear A with 20 teeth and gear B with 40 teeth.

Since the teeth of the gears must mesh, it will
take gear A two revolutions for every revolution
that gear B makes. If gear A is the drive gear,

moving at 100 RPM (revolutions per minute),
then gear B will turn at 50 RPM, half the speed.

At the same time, the amount of force that the gear is able to produce will be doubled.
Put simply, the force that is transmitted through the gears is an inverse to the speed. So
because the speed is halved in this case, the force is doubled.

However, this is the opposite of what happens in most water wheels. Rather than
reducing the speed, the desire is to increase it. So the gear that is on the water wheel’s
axle will be much larger than the one on the other. It’s not uncommon for the gear on the
water wheel to be eight or more times the size of the driven gear. As the leverage of the
water wheel produces a lot of force, the reduction of force caused by the increase in
speed is considered acceptable.

At times, multiple gears are strung together, which increases the ratio of teeth between
the drive gear and the driven gear. This allows much greater changes in speed than a
simple two-gear gearbox.

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