WATT’S EIDOGRAPH

Photographs of James Watt ‘s parallel eidographs have been found during the cataloguing and conservation of recently discovered photos at IMechE. These curious objects was designed to copy and create sculpture. Watt developed the machines at his home, Heathfield Hall. The photos were found with letters about the machine, they are freely available online.

Copying machine.
Copying machine.

Watt developed two sculpture-copying machines; one for same size copies and one for different sizes aka the Diminishing Machine. He was preparing patent drawings for them at the time of his death, some drawings which were found at the Hall are dated 1811. The contents of the workshop, including 24 multi-part moulds for plaster of Paris copying, and over 400 medallion moulds, casts and copies were transferred to the Science Museum in the 1920s but these photos are much earlier, being from 1883 when the workshop was first photographed (we think!).

The Diminishing Machine (see below) consists of a lathe bed, with fly-wheel and treadle for obtaining the motive power for driving the drill. There is a hollow tube long lever, fulcrumed at one end onto a ‘universal joint’, so that the other end can be freely moved about. The lever has a feeler (a blunt point) near its outer end and a drill near the fulcrum. Whatever the motion of the feeler, the motion of the drill is one-eighth part as much. The bust being copied is placed under the feeler, the feeler is then moved so to trace the bust. Plaster (or whatever material is being used) is placed under the drill; as the feeler traces the bust, the drill follows the same path cutting the plaster but at one-eighth the size of the original. The lever is balanced. On the bed of the lathe are various slides which are moved by a pentagraph (arrangement of levers) to give one-eighth as much motion to the new sculpture as to the original – this means everything is in proportion. Another motion allows for the turning around of the original and the copy. Examples remained of works cut on this machine, see below.

Watt chose for his subjects both people he knew and characters from classical antiquity, using portraits, busts and even his partner Matthew Boulton’s death mask! The copying machines were never finished, but working on them used many of the mechanical skills he developed in his engineering career, and no doubt he enjoyed the work.

The IMechE Proceeding article on the machines is freely available online to Members.

Archives, Institution of Mechanical Engineers

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