I think most people would be more than happy with it as is.

You may want to try a bit more lead as it looks like the grub screw in the eccentric is almost a 90 deg to the crankshaft web but not that easy to see for certain. If you move it another 10-20deg in the direction of rotation it may run a bit smoother at the ends of the stroke.

I was quite impressed at how slowly it will run. That means that there is not too much wrong with it. You have to expect a little bit of irregularity at slow speed, can be just slight variations in friction as it goes around.

John

You're wrong there! Bunch of engine junkies here. Mary Shelley's 'Frankenstein' is all about people like us. “You’re fulfilling your destiny, Dr_GMJN. Become my apprentice. Learn to use the Dark Side of the Force.” Bringing inanimate objects to life is dangerously addictive.

The irregular beats may be a feature of the engine's design. All engines of this type suffer from a geometric imperfection due to the 'angularity (or obliquity) of the connecting rod'. It's a consequence of converting reciprocating sideways into rotary motion. When the piston is centred in the cylinder, the connecting rod, being at an angle, isn't quite long enough to put the crank at a true right angle to the piston rod. This causes valve event timing errors. The error is proportional to the ratio between piston stroke length and con-rod length, and for it to be at an acceptable level the con-rod should be at least 4 times longer than the stroke. An inconvenient cure is to build engines with very long connecting rods. The other is to compensate errors with an adjustable valve gear and then spend an age fine tuning it. The Stuart's valve gear is a straightforward and effective compromise, with minor shortcomings, plenty good enough for a working model. However, if chasing perfection brings joy, then there are lots of more advanced engines to model…

Seriously good build though – you either have talent or a skip full of rejects, perhaps both! Congratulations.

Dave

Nice job, measure of success is not how fast it will run but how slow and that runs as slow as you could reasonably expect with a flywheel of that size. Well done indeed.

Paul.

Indeed. Yours runs fine as far as I can see, and a slow run is the most attractive because you can still see the detail of the moving parts, and it most resembles what you see in a full-sized engine of similar design. Plus I don't think the vanilla design of the 10V crankshaft is properly balanced – mine vibrates at high speed.

Because I don't have a quiet compressed air supply – I use a hand-held compressor from Lidl since the battery gave out in my car jump-starter/tyre inflator – I can scarcely hear the beat of my 10V.

I very much like your inlet control, and will shamelessly copy something like it…

Edited By Mick B1 on 18/10/2020 13:54:22

Something else to be aware of is that air and steam behave very differently, so steam runs better with more advance.

Also steam finds leaks that air can't (or at least makes them obvious!)

It is fun to fit a displacement lubricator and run a 10V on steam though, I found a coffee machine's milk frother supplied plenty of steam via a silicone tube for running unloaded.

Neil

Great work. To create something like this is not only addictive but fantastic for the soul. Well done, You seem to have taken to it like a duck to water. Now to plan the next one!

I find it interesting too. There's a mass of interest in a steam engine. Building them is great fun, and making them look good isn't easy either! Then there's understanding how they work, and how they might be improved. The more I look at the whole the more I appreciate the technical achievements of our forefathers.

Your diagram is every bit as good as mine I'm sure – I just drew it as it felt right to me.

I'm not sure about torque, but you may be right. Certainly the piston is travelling fastest at mid-point, because it has to slow down and reverse before hitting the end of the cylinder. Pressure inside the cylinder isn't constant throughout the stroke though. One of James Watt's major contributions was the Indicator Diagram, a graph of pressure inside the cylinder, example pinched from Wikipedia:

That it's all about heat is more obvious with hot steam than cold compressed air, but the piston isn't simply pushed to and fro by pressure. Rather, work is done as the input gas cools by expansion. So the valves aren't just opened and closed at each end with a bang, they gently open and close to maximise the expansion phase.

I find steam engines difficult to visualise because everything changes throughout the cycle; temperature, pressure, torque, power-output, piston speed, and rpm. My mathematical abilities run out of puff with rates of change. Wish I understood calculus but I struggle with the basics.

Measuring what an engine is capable of is another game. Next challenge: find the power output of your Stuart in Watts. I think average power is easier to measure than torque,but could be wrong…

Dave

I mean the input /output of the valve of course

I've got a question on direction of rotation.

How did you decide to run it that way?

I worked from the motorcycle engine I rebuilt under guidance from a friend nearly 50 years ago, and thought it should be clockwise when viewed from timing side.

I can't remember whether the Stuart sheets contained any instruction on that. Anyone know of standard conventions?