Stationary Engine Kits

Anthony Mount Models

Please note: Unfortunately this engine is currently unavailable.

M’ A de Polignac’s Curved Cylinder Engine

This engine was designed by M’ A de Polignac’s in France in the 1870s. The engine is unusual in that the cylinder is curved along its length. The piston is also suspended in a frame and swings like a pendulum. It was claimed that this form of construction relieved the cylinder of wear, and allowed for a fast running engine.

The engine was available from the catalogue of a M’ Oppennan. The design was published in a book of 1875, which had been edited in 1873. The illustration on which I based the model was for an engine of 6hp. As you can see from the illustration the engine is of light construction. A speed of 500 rpm was claimed, and that the engine had been tested to 750 rpm. It was a small engine with flywheels 500mm diameter. I chose a scale of 1/5 which gave a flywheel diameter of 100mm. The cylinder bore is 19mm diameter. The engine was used to drive woodworking machinery where the high speed was put to good use. Though it was originally a metric design I have used dual measurements on the drawings. Showing imperial first with the metric dimension below. You will notice that they are not exact conversions. Standard material sections have been used where possible.

The set of drawings comprise 20 in number plus a parts list, all to A4 size. Both metric and imperial dimensions are given on the drawings. There are five castings, an aluminium base, gunmetal for the cylinder, covers and eccentric strap. The rocking frame is a laser cut mild steel plate, as are the side frames, the webs being soldered on to represent castings. The flywheels and pulley wheel are machined from free cutting mild steel blanks. All other parts are made from bar and rod material.

The curved cylinder was machined full size using a horizontal boring machine and a large rotary table. In the model the curved bore was machined using a metal jig that was pivoted on the back of the cross slide. An extension being bolted to the back of the cross slide to get the pivot point far enough back. The other end was forked around the toolpost on the top slide. The top slide being used to apply the feed to a boring tool held in the chuck. The cylinder casting was clamped to the jig.

The engine runs very smoothly and is fascinating to watch in motion. It is quite a simple engine and can be machined on a 3 1/2” lathe. The laser cut frames save a lot of work. The connecting rod is an interesting piece of machining being fish bellied.

The engine was serialised in Engineering In Miniature from June 1995 to December 1995.