Machinery in an Overdrift windmill, note the Fantail and Common Sails

Diagram showing an Underdrift windmill

Brake Wheel and Windshaft.

Overdrift millstones

A Stone Nut in a Dutch Overdrift windmill

Open Trestle Post Mill with Spring Sails

Tower Mill with Roller Reefing Sails

Smock Mill with double Patent Sails

A cast iron Windshaft

Glossary of Windmill Terms

Bedstone

The Bedstone is the bottom of a pair of millstones. It does not move. The upper stone is called the Runner Stone.

Brake Wheel

The Brake Wheel is the main driving wheel in a Smock or Tower mill, and in some post mills. It is carried on the Windshaft and drives the Wallower on the Upright Shaft

Buck

The Buck is an East-Anglian term for the body of a post-mill.

Crown Tree

The Crown Tree is the central, single baulk of timber, usually oak, that rests on top of the post in a post mill. Attached to it are the side-girts and the rest of the frame of the buck.

Fantail

A fantail is a small windmill which is used to keep a windmill facing into the wind automatically.

Great Spur Wheel

The Great Spur Wheel is carried on the Upright Shaft It drives the Stone Nuts. Millstones driven by the Great Spur Wheel can be either Overdrift or Underdrift.

Head Wheel

The Head Wheel is carried on the Windshaft in a Post Mill and has a brake around its circumference. It drives a Stone Nut, Millstones driven by the Head Wheel are always Overdrift stones.

Overdrift

Millstones driven from above are known as Overdrift stones.

Pintle

The pivot centering a post mill on top of the main post.

Runner Stone

The Runner Stone is the topmost of a pair of millstones. It is driven by the Stone Nut. The lower stone is called a Bedstone.

Sails

The Sails are the source of power in a windmill. They are carried on the Windshaft. Most windmills had four sails, although some had five (Boston), six (Waltham, Lincs) or eight sails Heckington, Lincs and there is one recorded twelve sailed windmill (Cottenham, Cambs).

Common Sails have a lattice framework over which a sailcloth is spread. These were the earliest type of sails in northern European windmills.

Spring Sails, invented in 1772 by Andrew Meikle, have shutters adjusted by a spring. Each sail is adjusted individually and, as with Common Sails the mill has to be stopped to enable an adjustment to be made.

Roller Reefing Sails, invented in 1789 by Stephen Hooper, use a canvas strip wound around a roller in the place of shutters. The mill does not have to be stopped in order to adjust the sails.

Patent Sails, invented in 1819 by William Cubitt, combine the shutters of the Spring Sail with the automatic adjustment of the Roller Reefing Sail. Single Patents have shutters on the trailing side of the sail, Double Patents have shutters on both sides of the sail for its whole length.

Samson Head

An iron collar and plate bearing that fits over the pintle of a post-mill's post, that supports the weight of the crown tree, around which the buck of the mill is constructed. An example is visible at High Salvington windmill.

Stone Nut

The Stone Nut is a small gear driven by the Great Spur Wheel, Head Wheel, or Tail Wheel. It drives the Runner Stone either from above (Overdrift) or below (Underdrift).

Tail Wheel

The Tail Wheel is carried on the Windshaft in a Post Mill and drives a Stone Nut. Millstones driven by the Tail Wheel are always Overdrift stones.

Trestle

The Trestle is the substructure of a Post Mill, usually enclosed in a protective structure called a roundhouse, which also serves as a storage facility. Post mills without a roundhouse are called Open Trestle Post Mills.

Underdrift

Millstones driven from beneath are known as Underdrift stones.

Upright Shaft

The Upright Shaft is the main vertical shaft found in Smock and Tower mills. It is also found in some Post mills. It carries the Wallower at its top end, and a Great Spur Wheel at the bottom end. The Great Spur Wheel drves two or more Stone nuts.

Wallower

The Wallower is a driven gear at the top of the Upright Shaft in Smock, Tower and some Post mills. It is driven by the Brake Wheel

Windshaft

The Windshaft carries the Sails and also the Brake Wheel (Smock and Tower mills, and in some Post mills) or the Head Wheel and Tail Wheel in a Post Mill. Windshafts can be wholly made of wood, or wood with a cast iron Poll End (where the Sails are mounted} or entirely of cast iron.

References

See also

• "A Researcher's Guide to Local History Terminology" - Abecedary
• Glossary of mill terms