by Stewart Hart

By Ronald Binns

This engine was shown by Stewart Hart at a Sandown Park Model Engineer exhibition based on the design of Anthony Mount serialized in Engineering In Miniature magazine.

The original was patented by Joseph Simpson and James Alfred Shipton in 1848. It is a rotary steam engine, but it still uses connecting rods to drive the crankshaft. How many of these engines were built full size is unknown, but an engine was exhibited at the great exhibition in 1851 where it drove textile machinery

The ‘cylinder’, perhaps better described as a chamber, sits on a table carried on four short columns. Inside the chamber is a ‘piston’ lying on its side. Passing through the piston is an eccentric shaft, connected to the outer ends of the shaft are cranks. Connecting rods drop from these cranks to the crankshaft carried on bearings fixed to the base. Steam enters the chamber through a balanced slide valve and impinges on the side of the piston rolling it around inside the chamber.

The aim of this arrangement was to provide a compact smooth running engine. Construction of the model is quite conventional without any odd machining practices. It can be machined on a 3 1/2” lathe, the flywheel being 9” (225mm) diameter. There is quite a lot of milling involved. Castings are available for the base, table, cylinder, piston, covers, steam chest, steam chest cover, eccentric strap and flywheel. There are 23 drawings plus a parts list and all are of A4 size.

The engine has an interesting motion, with levers gyrating all over the place. It is also very free running and only requires a wisp of air to get it running. There is also a reference to the engine in The Engineer in 1862. Still with the same cylinder arrangement, but with a different drive mechanism.

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