Водяные молоты и кузницы доиндустриальной эпохи.

Pre industrial workshop utilizing water driven trip hammers
the historical mill or forge

A hammer mill, hammer forge or hammer works was a workshop in the pre industrial era that was typically used to manufacture semi finished, wrought iron products or, sometimes, finished agricultural or mining tools, or military weapons. The feature that gave its name to these workshops was the water driven trip hammer, or set of hammers, used in the process. The shaft, or 'helve', of the hammer was pivoted in the middle and the hammer head was lifted by the action of cams set on a rotating camshaft that periodically depressed the end of the shaft. As it rose and fell, the head of the hammer described an arc. The face of the hammer was made of iron for durability.

These mills, which were original driven by water wheels, but later also by steam power, became increasingly common as tools became heavier over time and therefore more difficult to manufacture by hand. The hammer mills smelted iron ore using charcoal in so called bloomeries (Georgius Agricola 1556, Rennherden, Rennfeuer or Rennofen: from Rinnen = "rivulets" of slag or Zrennherd from Zerrinnen = "to melt away"). In these smelting ovens, which were equipped with bellows also driven by water power, the ore was melted into a glowing clump of soft, raw iron, fluid slag and charcoal remnants. The iron was not fluid as it would be in a modern blast furnace, but remained a doughy, porous lump mainly due to the presence of liquid slag. These lumps of sponge iron, known historically as "blooms" were initially compacted by hand using a sledgehammer. After that they were forged several times, usually with the trip hammer or with sledgehammers until all the slag and charcoal had been removed. For that, the iron was heated in another forge oven or smith's hearth. The iron could then be directly used as soft iron. A further improvement process, such as fining as used in blast furnace operations, was not needed. The resulting coarse bar iron was then further worked externally e. g. in special, small hammer works (Zainhammer) into thin iron rods, (e. g. thick wire), so called rod iron (Zaineisen), which was needed by nailsmiths to produce nails. Further processing into so called refined iron or into "elastic" steel for e. g. for sword blades, was carried out by specialised refined iron hammer forges or by blacksmiths on site.

Geographically, hammer mills were dependent on the availability of water power. At the same time, there had to be forests nearby to produce the large quantities of charcoal needed. In addition, there had to be deposits of iron ore in the vicinity in order to ensure that there was only a short distance to transport the iron containing ores to the smelteries. Finally, agricultural land was needed in order to feed the many craftsmen involved.

In Austria the hammer mills were mainly found in the Iron Roots (Eisenwurzen) along the Austrian Iron Route around the tripoint of the states of Lower Austria, Styria and Upper Austria (e. g. Ybbsitz) and in the Upper Styrian valleys of the Mur and Mürz and their side valleys. The seats of the hammer lords ("black counts") were known as Hammerherrenhäuser ("hammer lord manors").

Steelworkers in Thiers, France used hammer mills, powered by the Durolle River in the Vallée des Rouets, for the production of knives and other cutlery until the middle of the 19th century.

Hammer mills were not widespread in England, but there are examples such as the one at Abinger Hammer in Surrey from which the village derived its name.

Most of the mills listed here have survived and are open to the public.

In the literature, hammer mills were immortalised in Friedrich Schiller's ballad, Der Gang nach dem Eisenhammer (1797), which Bernhard Anselm Weber set to music for the actor, August Wilhelm Iffland, as a great orchestral melodrama, and later by Carl Loewe as a through composed ballad.