Introduction
- Types of Mill
There are three kinds of
windmill. The earliest of these is the post mill, which consists
of a box-like structure of wood, containing all the machinery.
This can be turned into the
wind on a central upright post.
Later came the tower mill, which
is built of brick or stone, except for the revolving cap on the
top; and the smock mill,
which is similar to the tower mill, but has wooden tower with six
or eight sides, often on a
brick base.
Shipley is an eight-sided smock mill, so-called because
she is supposed to look like the old-fashioned farm labourer's
smock.
Outside of the Mill
Before you start your visit, go outside and look up
at the Mill. You can see that she is built on a brick
base, which is two stories high. Above that there
are three more stories of wooden tower, tapering
towards the top.
On the very top is the cap,
perched like a hat on top of the wooden tower.
The cap carries the sails, which in this part
of the country are always known as sweeps. At
the back of the cap is the fantail, another little windmill, set
at right angles to the sails. The
wind blowing against the sweeps causes them
to rotate.
For the Mill to work, it is necessary for the sweeps to be facing
directly into the wind. To do
this the whole cap must be turned. This
is done automatically by the fantail. The fantail
turns when the wind blows on it from one side,
driving a series of gears, connecting to a worm which in turn
mates with a toothed ring on
the top of the smock tower, known as the curb. It is on this curb that the cap rests and turns.
The cap has no wheels - it slides on greased iron plates
on the top of the curb.
The whole cap, together with the sweeps, fantail and
gearing weighs about fourteen tons.
The
Sweeps
 The
shuttered sweeps fitted to Shipley
Mill are of the type known as Patent
Sails. Invented by an engineer called William Cubitt in 1807, their big advantage is that they can be adjusted without the need to stop the Mill.
Each of the four sweeps carries a set of shutters, which can be opened and closed like a Venetian blind, by the movement of the
uplongs, long wooden rods to which the
shutters are connected. At the centre of the four sweeps, the
uplongs are coupled to the
spider, which connects through
links and triangles to the striking
rod, an iron bar that goes right through
the windshaft, which carries the
sweeps. At the back of the mill the striking
rod connects to the chainwheel, from which is hung an endless chain, reaching down to the stage
outside the second floor of the Mill. The striking weight is hung on this chain to hold the shutters
either open or closed. The speed of the Mill can be regulated to
some extent by altering the
weight; a heavy weight will hold the shutters tightly closed in a light breeze, while a lighter
weight can be used in a strong wind to allow the shutters
to open slightly in the gusts. Ten to twelve turns per minute of
the sweeps
is a good speed for grinding.
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