The Lap Engine is a

beam engine A beam engine is a type of steam engine where a pivoted overhead Beam (structure), beam is used to apply the force from a vertical piston to a vertical connecting rod. This configuration, with the engine directly driving a pump, was first used b ...

James Watt James Watt (; 30 January 1736 (19 January 1736 OS) – 25 August 1819) was a Scottish inventor, mechanical engineer, and chemist who improved on Thomas Newcomen's 1712 Newcomen steam engine with his Watt steam engine in 1776, which was f ...

, built by

Boulton and Watt Boulton & Watt was an early British engineering and manufacturing firm in the business of designing and making marine and stationary steam engines. Founded in the English West Midlands around Birmingham in 1775 as a partnership between the Engl ...

in 1788. It is now preserved at the

Science Museum, London The Science Museum is a major museum on Exhibition Road in South Kensington, London. It was founded in 1857 and is one of the city's major tourist attractions, attracting 3.3 million visitors annually in 2019. Like other publicly funded ...

. It is important as both an early example of a beam engine by Boulton and Watt, and also mainly as illustrating an important innovative step in their development for its ability to produce rotary motion. The engines name comes from its use in

Matthew Boulton Matthew Boulton ( ; 3 September 172817 August 1809) was an English businessman, inventor, mechanical engineer, and silversmith. He was a business partner of the Scottish engineer James Watt. In the final quarter of the 18th century, the par ...

Soho Manufactory The Soho Manufactory () was an early factory which pioneered mass production on the assembly line principle, in Soho, Birmingham, England, at the beginning of the Industrial Revolution. It operated from 1766–1848 and was demolished in 1853. B ...

, where it was used to drive a line of 43 polishing or

lapping Lapping is a machining process in which two surfaces are rubbed together with an abrasive between them, by hand movement or using a machine. Lapping often follows other subtractive processes with more aggressive material removal as a first ste ...

machines, used for the production of buttons and buckles.

Innovations

Watt did not invent the

steam engine A steam engine is a heat engine that performs Work (physics), mechanical work using steam as its working fluid. The steam engine uses the force produced by steam pressure to push a piston back and forth inside a Cylinder (locomotive), cyl ...

and there is no single '

Watt steam engine The Watt steam engine design was an invention of James Watt that became synonymous with steam engines during the Industrial Revolution, and it was many years before significantly new designs began to replace the basic Watt design. The Newcomen ...

' as such. He developed a number of separate innovations, each of which improved the existing engines of the day, beginning with Newcomen's. The Lap Engine of 1788, also the Whitbread Engine (1785), represent survivors of the first engines to show all of Watt's major improvements in one.

Parallel motion

Rotative beam engines

Sun and planet gear

The

rotative beam engine A beam engine is a type of steam engine where a pivoted overhead beam is used to apply the force from a vertical piston to a vertical connecting rod. This configuration, with the engine directly driving a pump, was first used by Thomas Newcomen ...

needs a means to convert

reciprocating motion Reciprocating motion, also called reciprocation, is a repetitive up-and-down or back-and-forth linear motion. It is found in a wide range of mechanisms, including reciprocating engines and pumps. The two opposite motions that comprise a single ...

of the piston and beam to

rotary motion Rotation or rotational/rotary motion is the circular movement of an object around a central line, known as an ''axis of rotation''. A plane figure can rotate in either a clockwise or counterclockwise sense around a perpendicular axis intersec ...

. The

crankshaft A crankshaft is a mechanical component used in a reciprocating engine, piston engine to convert the reciprocating motion into rotational motion. The crankshaft is a rotating Shaft (mechanical engineering), shaft containing one or more crankpins, ...

was well known for centuries before Watt, mostly from its use in mining machinery powered by

water wheel A water wheel is a machine for converting the kinetic energy of flowing or falling water into useful forms of power, often in a watermill. A water wheel consists of a large wheel (usually constructed from wood or metal), with numerous b ...

s. However its use for a steam engine was covered by

James Pickard James Pickard was an English inventor. He modified the Newcomen engine in a manner that it could deliver a rotary motion. His solution, which he patented in 1780, involved the combined use of a crank and a flywheel. James Watt's company Boulton ...

's patent at this time. Watt was unwilling to pay a license fee to use the crank and so sought an alternative. The sun and planet gear was invented by another Scottish engineer,

William Murdoch William Murdoch (sometimes spelled Murdock) (21 August 1754 – 15 November 1839) was a Scottish chemist, inventor, and mechanical engineer. Murdoch was employed by the firm of Boulton & Watt and worked for them in Cornwall, as a steam engin ...

, an employee of

. Watt patented it in October 1781. The sun and planet gear is a simple epicyclic gear. The planet is attached rigidly to the end of the

connecting rod A connecting rod, also called a 'con rod', is the part of a reciprocating engine, piston engine which connects the piston to the crankshaft. Together with the crank (mechanism), crank, the connecting rod converts the reciprocating motion of the p ...

, hung from the beam. As it rotates it applies a torque to the sun gear, just as for a crank, and so causes it to rotate. As the two gears also rotate relative to each other, like conventional gearwheels, this has the effect of giving the sun gear a further rotation. The sun, and the output crankshaft, thus rotates twice for every piston cycle of the engine, twice as fast as with a conventional crank. Beam engines were slow-moving and the output shafts driven by the Lap Engine were fast-moving, so this was an advantage.

Centrifugal governor

According to the Science Museum, it was the first steam engine to be fitted with a

centrifugal governor A centrifugal governor is a specific type of governor with a feedback system that controls the speed of an engine by regulating the flow of fuel or working fluid, so as to maintain a near-constant speed. It uses the principle of proportional con ...

Innovations

Parallel motion

Rotative beam engines

Sun and planet gear

Centrifugal governor

History

Preservation

Notes

References

Further reading