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Windmills use conical cogs, straight cogs and staves to transfer power from the sails to the millstones and sack hoist.
Top photo: The sails, windshaft and brake wheel are the only mill components that rotate horizontally. The main spindle, stone spindles and millstones turn vertically. Conical cogs on the brake wheel and the wallower are used to change the "direction of rotation" from horizontal to vertical.
Bottom photo: Straight cogs are on the great spur wheel (at the bottom of the main spindle). Staves are on the stone nut (at the top of the stone spindle). Straight cogs and staves are simpler in design than conical cogs because both spindles rotate in the same direction (vertically).
The number of cogs in each wheel must not be divisible by each other. For example, a great spur wheel cannot have 99 cogs when a stone nut has 33 cogs. This maximizes cog life because each cog must contact all other cogs or staves with the same frequency.
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