I am not an engineer, but my father, Tony Lewis, was the engineering teacher at Te Puke High School and I was in his class for four years.  When Dad died in 2014 he left me the Boxford Model A lathe that he bought from the school when they upgraded. We normally lived in the Smokey Mountains of Tennessee, USA,  but we bought a house in Thames, New Zealand to put the lathe in and as a holiday house, and where we were very happily caught by lockdown, and plan to stay.

I started re-learning how to use the lathe and have now made a number of  YouTube videos about it and more waiting to be edited. https://YouTube.com/c/Evanecent

My grandfather was a stationary steam engine engineer who built a Hero steam

engine (above - before and after restoration) which I inherited. As a result of that I was asked to give a lecture on the history of steam engines, starting with the Greeks, for Heritage Festival. The lecture is on my YouTube Channel. That was my introduction to steam engines although I had been dreaming of making one since I was in my early teens and saw an oscillating cylinder engine for the first time.

My first project was to build a Hero’s steam engine and measure its power output and efficiency. It was capable of rotating at 5,400 revolutions per minute (the highest speed ever reported).

To demonstrate that it could perform useful work it was connected to a gearbox to reduce revolutions per minute to 122 RPM or less. This was used to lift a weight on a small crane and it lifted 200 to 300 grams to a height of 500 mm in about 15-18 seconds. From that it was calculated that it produced about 0.1 Watts of power. This is considerably less than the power output calculated from the theory of thrust produced by steam jets, which was up to 9 Watts.

This proved that it could do work, but whether it would be considered useful work is another story.The efficiency of converting heat to mechanical work was calculated from theory to be 1% but in practice was as low as 0.0128%.

Efficiency may not matter if there is an unlimited supply of fuel, such as wood, to produce the fire necessary to generate steam. On the other hand, if it takes more labour to collect the fire wood than it saves in providing mechanical energy, perhaps it was not economic.

It could, however, have been the beginning of the development of more efficient steam engines. Some engineers disagree saying that they did not have the knowledge (thermodynamics, fluid dynamics, gear design, and boilers) to develop it further, but that is debatable. Trial and error goes a long way.

Many people have said that it produces so little torque that simply placing your finger on the ball will stop it spinning. They considered it a useless toy. In a machine with a rotating shaft, like the Hero engine, torque is the force that it can exert at a given radius from the axle (given in pound.feet or Newton.meters).

Power can be calculated by multiplying the speed of rotation (revolutions per minute or RPM) by torque. The fact that the Hero engine can spin at a very high rate, means that it could be geared down to produce more torque. If it is geared down to produce slower rotation the torque increase as the rate of rotation decreases, but the power remains the same.

I made a worm gear that turns one time for every 44 turns of the input shaft. By reducing RPM by a factor of 44 we increase torque by a factor of 44 and this gives it enough torque to operate a crane and lift a weight (power stays the same).

The worm gear consists of a thread (20mm diameter with 1.5mm pitch) meshing with a gear wheel which has 44 teeth. For every turn of the thread it advances by one tooth, so it takes 44 turns of the shaft to make the gear wheel turn once. This type of gear reduction should produce relatively little friction.

This engine was built using a small engineer’s lathe and during its production a series of YouTube videos were produced, including a very simple method for making the worm drive gear.

How did Hero’s steam engine work?

The moving part was a spinning sphere with jets placed on its equator pointing along the equator. Steam rushing out of the jets created a force that made the sphere spin.

It wasn’t until 1690 AD that Sir Isaac Newton proposed the three laws of motion that we still use today. The third law states that “Every action produces a reaction equal in force and opposite in direction.” In this case the force that causes the steam to rush out of the jets causes an equal and opposite force on the jet itself and that makes the sphere turn. This is the same way that rockets, jet engines and other aircraft engines work.

My first version (below) was based on my grandfather’s engine. My grandfather, Hugh Sargeant Barrett, made his model by using a large copper kettle as a boiler (3.5 litres) to produce steam which was conducted up vertical pipes. These pipes supported a copper sphere (which had been the float in a toilet cistern) supported between two pointed pivots. ran at 2400 RPM.

Modern turbines can exceed 30,000 RPM. The absolute maximum speed (if the jets of Hero's engine were able to reach the speed of sound) was calculated to be 60,000 RPM. But as the jets approach the speed of sound their thrust diminishes towards zero. This means that the jets might be able to approach the speed of sound (mach 1), but can never reach it.

In reality Hero's engine only reached 5,400 RPM with jet velocity of about one eleventh of the speed of sound in steam, and actual air speed of 122 km/h or 73 MPH.

Improved versions in part two here.