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This type of engine was used to
drive machinery which had previously been driven by horses and, customers always asked
James Watt, " how many horses will your engines replace". The term horsepower has been in use ever since, and when customers ordered engines of this size, they were told it would do the work of ten horses. |
| The piston of this
engine was powered in both directions by, the expansive force of steam and a vacuum
created inside Watt’s separate condenser. The Lap Engine is the first engine in the
world to have its rotational speed controlled by a centrifugal governor. |
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| In 1788 this engine drove forty three
individual machines which were used for the lapping and polishing of small manufactured
articles. The main structure of the engine is made from English oak all held together with wrought iron straps and bolts.
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| However, in the Science Museum where it is now preserved it is not assembled as it was used originally . It is now displayed with the lower half of the flywheel below the working floor level. At the Soho Manufactory the whole diameter of this wheel was above the factory floor as can be seen on the Lap Engine in miniature. | |
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The flywheel of this engine is 16 feet in
diameter and was fitted with 304 wooden gear teeth, these teeth were used to drive a
counter shaft which drove each individual lapping and polishing machine. The model is the result of an extensive search to rediscover what the engine originally looked like when James Watt had designed it in 1788. The Lap Engine was used to produce the blanks which were used for the Boulton Coins in 1797, the most notable was known as the cartwheel, a heavy copper coin valued at two pence. Note the Sun and Planet method of rotation, fitted to avoid any infringement of the Pickard patent.
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