A mill is a device, often a structure, machine or kitchen appliance, that breaks solid materials into smaller pieces by grinding, crushing, or cutting.

Milling also refers to the process of breaking down, separating, sizing, or classifying aggregate material (e.g. mining ore).

For instance rock crushing or grinding to produce uniform aggregate size for construction purposes, or separation of rock, soil or aggregate material for the purposes of structural fill or land reclamation activities.

Mining engineers, Peter von Rittinger, Friedrich Kick and Fred Chester Bond independently produced equations to relate the needed grinding work to the grain size produced and a fourth engineer, R.T.Hukki suggested that these three equations might each describe a narrow range of grain sizes and proposed uniting them along a single curve describing what has come to be known as the Hukki relationship.

[5] Autogenous or autogenic mills are so-called due to the self-grinding of the ore: a rotating drum throws larger rocks of ore in a cascading motion which causes impact breakage of larger rocks and compressive grinding of finer particles.

Ball mills are commonly used in the manufacture of Portland cement and finer grinding stages of mineral processing.

Industrial ball mills can be as large as 8.5 m (28 ft) in diameter with a 22 MW motor,[6] drawing approximately 0.0011% of the total world's power (see List of countries by electricity consumption).

However, small versions of ball mills can be found in laboratories where they are used for grinding sample material for quality assurance.

The bearing units of one roller can move linearly and are pressed against the material bed by springs or hydraulic cylinders.

A similar type of intermediate crusher is the edge runner, which consists of a circular pan with two or more heavy wheels known as mullers rotating within it; material to be crushed is shoved underneath the wheels using attached plow blades.

However, the smaller the rods, the larger is the total surface area and hence, the greater the grinding efficiency.

SAG mills are primarily used at gold, copper and platinum mines with applications also in the lead, zinc, silver, alumina and nickel industries.

A VSI mill throws rock or ore particles against a wear plate by slinging them from a spinning center that rotates on a vertical shaft.