A Coarse Guide to the Steam Locomotive for ‘N’ Gauge Modellers

[PennineWagons]

an appointment where a charming lady hit me with a hammer for half-an-hour and then stated, "It's getting worse."

Well you were advised, John, that 'Nurse Whiplash' did not sound like a genuine healthcare professional.
PW

[martyn]

Sorry to go back a few posts, but the RCTS LNER history does point out that the 'Castle' class had had seventeen years of development through the 'Star' class before the trials against the A1: which had only three years development.

However, there is no doubt the A1 was well behind the 'Castle' performance.

And the trials of the latter on the LMS effectively killed the proposal for a Derby designed Pacific, which wouldn't appear on the LMS until the Stanier era.

Martyn

[F2Andy]

Great series of articles!

My computer-thingy doesn't have MS 'Word', so, unfortunately, I'm not able to use it for for drafts.  ...

If your computer is Windows, you can use Notepad, which is part of Windows. Tap the windows button, and type "NOT" and it should appear. If you use a Mac, there is, I think, an equivalent called TextEdit.

Both are very basic, but perfectly fine for writing a draft for a forum post.

[Foxhound]

Well, I have just spent a few lunch breaks wading through this thread and I have to say @Train Waiting that this is an incredible work, and very engaging. I now understand far more than I ever did about those water boiling devices that my diesel-soaked brain would ever admit to, and I am now far more inclined to purchase a 'kettle' for my layout.
I am torn, however, between a Castle, a Black 5, a Bulleid or an A4. Maybe I should buy one of each?

[grumbeast]

I am torn, however, between a Castle, a Black 5, a Bulleid or an A4. Maybe I should buy one of each?

Yes.  This.  Actually, you've given me an idea, The only one I don't have is a Black 5 (how did that happen?).

Wonderful latest article John, I'm slowly beginning to understand the purpose and importances of a good superheater.  I have always been a huge fan of Castles (I think a far more effective and useful locomotive than the Kings, pound for pound) and I think Martyn's addendum about the pipe interior and shape considerations was very insightful and something I've not thought about before

Graham

[Train Waiting]

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 44


Hello Chums

At Last, We Get to the Engine/s

Please think of a fire engine.  What did you imagine?  A big red lorry rushing round skooshing water at conflagrations?

In the second decade of the eighteenth century, it meant something different.  You see, in 1712, Thomas Newcomen developed a practical 'Atmospheric Engine' which was often called a 'Newcomen Fire Engine'.  Nowadays, we generally refer to it as a 'Newcomen Engine'. This is generally accepted as the world's first successful steam engine.

As is so often the case, Mr Newcomen had at his disposal the work of others who had experimented with various steam contraptions over the years. Worth mention is Denis Papin FRS, who had experimented with an atmospheric engine which used a piston moving in a cylinder.

The Newcomen engine works by drawing steam at about 2 psi, generated in a boiler below the engine, into a vertical cylinder. Once the cylinder is full of steam and the piston is at the top, the exterior of the cylinder is sprayed with water which condenses the steam.  This creates a partial vacuum in the cylinder which allows atmospheric pressure to push the piston down the cylinder.

The main use for Newcomen engines was to pump water out of mines.  The piston was connected to a rod which, in turn, was linked to a horizontal beam, pivoted in the centre.  The other end of the beam was connected to the pump. Many of these engines were built during the eighteenth century and they are regarded as the beginning of commercial steam power.

James Watt made many improvements to the Newcomen engine and is particularly remembered for the invention of the separate condenser.  In partnership with Matthew Boulton, their firm, Boulton & Watt, became leading builders of steam engines.

Mr Boulton was, it seems, keen to exploit steam power beyond pumping mines and encouraged James Watt to develop an engine where the reciprocating movement of the piston could be made into a rotary motion for driving machinery and suchlike.

Whilst a crank would have been the most simple solution, a chap called James Pickard had been granted a patent for the arrangement they would have used.  This caused them to devise a 'sun and planet' gear in 1781.  Steam power quickly moved from mines to manufactories and the industrial revolution was proceeding apace. Although he had a patent for a high pressure steam engine, the term was relative and James Watt resisted the use of substantially higher steam pressures on safety grounds.   

Although a footnote to history, it would be wrong not to mention Nicolas-Joseph Cugnot, a French military engineer, who built what is accepted as the first self-propelled mechanical land vehicle. Known as the fardier à vapeur it was, effectively, a steam-powered cart.  During 1769-1770, he built, I believe, three prototypes, two of which were full-sized.  The drive from the piston to a wheel was by means of a ratchet apparatus.

I have used three terms, in that brief overview of developments, to which I wish to return briefly.  These are the vital components which turn a xxxxx (please insert your own favoured type) from a boiler on wheels into a steam locomotive.

Cylinder, piston and crank.  Interestingly, the concepts go back about a couple of millennia, and they were in use in Roman times.  Although not quite as we'll be using them.  Still, the basic components of a steam engine were nothing new.

Waggonways, primarily to allow a horse to pull a heavier load, usually of coal, had been around for centuries and became fairly common after 1700.

Once James Watt's patent expired, Richard Trevithick led the way in the use of higher working pressures, around 30 psi (sometimes, during the period, called 'strong steam') from 1800. James Watt did not approve.

All these developments came together in Merthyr Tydfil, on 21 February 1804, when Richard Trevithick demonstrated the world's first steam-powered locomotive hauling a train along the tramway of the Penydarren Ironworks.  And, nearly two-and-a quarter centuries later, we are still building steam locomotives.  Hats off to Trevithick.

It's a great shame he never achieved the commercial success he deserved and ended up, in 1827, penniless on a quayside in South America.  Incredibly, he met, literally, with good fortune because (you know what it's like to go away on holiday and meet one's neighbours) he met Robert Stephenson.  As you might have noticed, I hold the Younger Stephenson in exceptionally high regard.

Mr Stephenson paid for Richard Trevithick's fare for the voyage home. History records he gave Mr Trevithick £50.00.  In to-day's money, that's getting on for 2,500 of these:-





For the next part of this mini-series, I'll fast forward through the period of the earliest steam locomotives, what I call 'Steam Dinosaurs', and centre our discussion on the 'engine/s' part of the kind of steam locomotive we might run on our layouts or see at a heritage railway.  However, before getting into all that, I was keen to note the historical context with a special mention to Richard Trevithick.


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Toodle-pip

John

[Papyrus]

Many thanks for the latest instalment, John. The early history of the steam engine is a fascinating subject. As with so many other things, the real pioneers like Newcomen and Trevithick are often overlooked and those who are remembered today were the ones who 'stood on the shoulders of others', to quote Isaac Newton.

Your mention of the Cugnot steam cart brought back a memory from my teenage years. I built a plastic kit of one (can't remember the maker now) and I had completely forgotten about it until now. Naturally, I consulted Professor Google and came up with this. I hadn't realised one was still in existence.

Cheers,

Chris

[Bealman]

Fascinating stuff, John.

[Train Waiting]

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 45


Hello Chums

Before we time-travel over centuries in a sentence, I'd like to pause for a second to thank you for the thoroughly kind comments which you have posted since the mini-series recommenced. And, of course, for the 'reactions'.  These are hugely appreciated and encourage me to continue. Right-oh; on with the mini-series, where were we...

From the Ancients to the Steam Shed

We saw, in the previous part, that the key components of a steam engine: cylinder, piston and crank were known about and were being used, albeit for different things, when BC became AD. (No, I'm not in favour of the terms BCE and CE.)  The other component required to convert reciprocal movement to rotary motion and, indeed, vice versa is the connecting rod and there appears to be evidence that this was in used (in the vice versa sense) in Roman (at least) times to convert rotary motion to reciprocal to move power saws.

Cylinder - piston - connecting rod - crank: here we are fast-forwarded:-





From the rear of the cylinder projects the piston rod.  One end is connected to the piston which, I invite you to imagine, is inside the cylinder.  The other end is attached to the crosshead.  The crosshead is moved to-and-fro by the action of the piston and its movement is kept where it ought to be by it sliding along slidebars.  This locomotive has two prominent slidebars, one above the crosshead and one below.  Locomotive designers enjoyed different crosshead and slidebar arrangements, but the principle remains the same.

Pivoting on the crosshead is the small end of the connecting rod.  The big end of the connecting rod sits on the crankpin, which projects from the crank.  The radius of the crank is half that of the distance the piston moves in the cylinder - called the stroke.

In two paragraphs we have introduced reciprocal, pivoting and rotational movement, all of which requires suitable bearing surfaces and lubrication.  Think of the driver going diligently around the locomotive with his oil can.

At this point, if you have tinkered with old motor-bicycles or motor-cars during your life, you might wonder why the steam locomotive has a piston rod and a crosshead.  Internal combustion engines manage happily without these, having the connecting rod pivoted from a gudgeon pin in the piston.

There are two reasons for this:

1. The distance from the piston to the crank is a lot further in a steam locomotive.  Add to this the forces involved and there is a requirement for a long and heavy connecting rod.  It makes sense to have it well-supported at its small end.

b. This one is a fundamental point which we need to understand.  Pistons in an internal combustion engine are single-acting - they are forced in one direction by the mixture exploding and are returned by the crankshaft via the connecting rod.  A two-stroke engine has one power stroke for each revolution of the crankshaft and a four stroke engine has one power stroke for two revolutions of the crankshaft (assuming single-cylinder engines).

Please think about that.  For every four times the piston in a four-stroke internal combustion moves along the cylinder, it produces power once only.  The other three times, it is using power.

Newcomen engines and those derived from them had single-acting pistons.  Then James Watt transformed the situation by making the piston double-acting, producing power with each stroke.

And that's what a steam locomotive does - each piston stroke is a power stroke, which means the piston has two power strokes per revolution of the crank.  We'll discuss how this is achieved later but, for now, can we please accept that the clearances required to allow the connecting rod to pivot in the piston would be such that the steam would escape to atmosphere?

The steam engine has another advantage over an internal combustion engine.  Let me choose a motor-bicycle, say a Brough Superior 'SS100' vee-twin like TE Lawrence enjoyed.  I sit astride it, turn on the petrol, tickle the Amal carburettor, ease open the twistgrip and... Nothing!  I could sit there all day and nothing would happen.  Same for your petrol or diesel motor-car.

Of course, you could activate the starter motor and I could give the JAP engine a 'long swinging kick' with the kickstarter and we'd both be away.

Have you ever seen the fireman attempting to kickstart a '9F'?  Or seen the driver press the button for the electric starter?  No.

Why's that then? Because the double-acting steam engine starts itself when steam is applied.  Or, it usually does.

Clever stuff this, and please remember it's a technology that's a couple of centuries old.

Some of the earliest locomotives had only one cylinder but two quickly became the norm.  The disposition of the piston at top or bottom dead centre, and the subsequent location of the crank, might mean a single-cylinder steam engine was in a 'blind spot'.  Single-cylinder traction engines, should they suffer this inconvenience, can be given a little push on the flywheel and off they jolly well go.

A driver can still be unlucky with the disposition of the pistons of a locomotive, which might refuse to start, say, when leaving a station.  He would deal with this by putting the locomotive into reverse and moving back a tad, then into forward gear and away. So much easier with Jimmy Stirling's steam reverser as fitted to locomotives of the Glasgow & South Western and South Eastern Railways.

Next, we'll discuss where the cylinders are located (normally - no backwoods 'Shay' or other types will intrude).  Probably a little later, we'll even encounter locomotives with more than two cylinders.  Anyone know which British railway first introduced a four-cylinder locomotive?

Finally, you might have seen me use the form, 'engine/s', in a couple of previous postingtons.  It was just me hinting about something that might have become apparent from what I've written above.  Each cylinder - piston - piston rod - connecting rod - crank grouping on a steam locomotive is, effectively, an engine in its own right.  Perhaps, something worth keeping at the back of one's mind.  The point having been made, I'll use 'engine' from now on.


'N' Gauge is Such Fun

Many thanks for looking and all best wishes.

Tickety-tonk

John



   

[crewearpley40]

A thank you from me John on the history and engineering lessons

Maybe you should be be a Railway author

Happy new year.  Chris

[martyn]

Thanks again, John.

As an aside, I think the big marine diesels of today are classified as 'trunk' (without crosshead-not sure, I was a navigator at sea....), or crosshead type, if so fitted.

I think also a two stroke of any number of cylinders fires once per rev, as opposed to once every second rev of a four stroke (?). (or maybe I've misunderstood your post).

There were/are a few designs of internal combustion engines that were double action, at least some marine diesels; and I think the ill-fated Kitson-Still loco was also double acting but with steam on one side of the piston and diesel on the other! However, it wasn't that simple, as steam at one end of the piston was used to start, and at 4 mph, diesel was injected into the other end of the cylinder and steam shut off.

Martyn

[chrism]

I think also a two stroke of any number of cylinders fires once per rev, as opposed to once every second rev of a four stroke (?). (or maybe I've misunderstood your post).

"A two-stroke engine has one power stroke for each revolution of the crankshaft and a four stroke engine has one power stroke for two revolutions of the crankshaft (assuming single-cylinder engines)" - I think you missed the bit in brackets.

[martyn]

I think also a two stroke of any number of cylinders fires once per rev, as opposed to once every second rev of a four stroke (?). (or maybe I've misunderstood your post).

"A two-stroke engine has one power stroke for each revolution of the crankshaft and a four stroke engine has one power stroke for two revolutions of the crankshaft (assuming single-cylinder engines)" - I think you missed the bit in brackets.

Quite right, Chris.

Thanks for that.

Martyn

[Train Waiting]

Thank you very much, Chums.

A four-stroke single only 'fires' one every second revolution of the crankshaft.  This leads to some interesting sounds. A 'Big Pussy' (Panther 650 cc ohv single - built in Cleckheaton) 'firing once every lamp-post', or a racing machine in Poppingham's time sounding like nothing else on earth.  No hairs left on the back of my neck.  The film features Stanley Woods on a Works 'KTT' Velocette 350cc ohc single.

 


I've owned several 'Velos' in my time, but only ohv models.

With all good wishes.

John

[Train Waiting]

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 46


Hello Chums

Where to Put the Cylinders

Continuing from where we left off, discussing two-cylinder steam locomotives, there arises the matter of where to place the cylinders.  At the front of the locomotive is obvious, to allow an easy route for steam from the boiler, often called 'live steam', to get into the cylinders and for steam that has been used in the cylinders, called 'exhaust steam' to get away and straight up the chimney.  Please note, I an skipping gazelle-like around the matter of the Franco-Crosti '9F' 2-10-0s.  What a waste of money that wheeze was.

In the early days, the cylinders were outside of the locomotive's frames and there are pictures of these earlier in the mini-series.  Then Robert Stephenson had an idea - he placed the cylinders of his Planet 2-2-0 of 1830, for the Liverpool & Manchester Railway, between the frames.  This arrangement is what is known as an inside-cylinder locomotive.  The type dominated locomotive construction for British railways during the 19th Century and only gradually became less prevalent in the 20th Century.

*

Let's pause for a Fun Fact.

The last inside-cylinder tender engine to be built for a main line British railway was '2251''Collett Goods' 0-6-0 No. 3219, built for BR (WR) in January 1948.

Inside-cylinder tank engines were built even later, the final one for BR being '9400' 0-6-0PT No.9499 in July 1955.  She barely saw four years' service.

*

Now for a couple of picturinghams:-

An 'Adams 'Radial' 4-4-2T outside-cylinder locomotive:





And an inside-cylinder locomotive - a Hunslet 'Austerity' 0-6-0ST, this one being an LNER 'J94':





Can you imagine it?  Railway Bylines magazine Volume 30, Issue 2, January 2025, has a picture, on page 97, of a NCB driver standing beside an Austerity' 0-6-0ST.  The caption tries to persuade us the he is oiling the connecting rod bearings.  My emphasis.  A glance at @Nbodger 's splendid photograph (above) of his 'Austerity' leaves us in no doubt that she's an inside-cylinder locomotive with connecting rods between the frames.  The driver would have been attending to the coupling rods.

It's bad enough when modellers make that fairly common error of terminology, never mind Railway Bylines. 

And what about people wittering on about a train's 'consist'?  Fine for the Seaboard Air Line, but not 1950s BR.  Grrr!

*

Although inside-cylinder locomotive were, by far, the most common type during the 19th Century, their dominance was never complete.  Some designers preferred outside cylinders for at least some of their locomotives - a good example being William Adams, best known for his work on the London & South Western.  They were also normal on narrow-gauge lines, for obvious reasons.

When 'Atlantic' 4-4-2 engines started appearing, outside cylinders were the norm, although Mr Aspinall's famous 'Highflyers' for the Lancashire & Yorkshire had inside cylinders.

And there was one important British main line railway which had a total of five inside-cylinder engines (all tank engines, by the way) in its total locomotive stock until a new Locomotive Superintendent took over in 1896. Then inside-cylinder types began to become common on the line, or, at least, parts of it.  Any idea which railway?

*

Although few 'N' gauge modellers will model inside cylinders, many of us will mention them.  Which made me think that we had jolly well see them.  Not easy, because like a Victorian lady, inside-cylinder locomotives keep their interesting bits well-hidden.  Still, here's a coarse picturingham I made from an old illustration in my non-collection:





The fine chaps are have such fun taking this 0-6-0ST to bits.  The boiler is off, as is the buffer beam, which allows us a SuperSpiffing view of the cylinders with their covers removed.

The left-hand (Viewed facing forward from the footplate) piston can be seen, right at the end of its stroke.  Just look at that nut securing the piston rod - Mr Whitworth's finest.

The right-hand piston cannot be seen.  Unless the chaps have removed it, I assume it's in the cylinder, half-way down.  Please ignore the space between the cylinders - that's for thinking about later.

*

Now for the tricky bit of explanation.  And I'm going to be brave and slip in a bit of modellers' jargon as well.

Why's the right-hand piston half way down the cylinder and not at the opposite end?

Well, if the pistons were at opposing ends of the cylinders, the chance of the locomotive stopping in a 'blind spot', with both pistons on dead centre, would be high.  The cranks on the locomotive would be set at 180^o and, if the engine was in a good state of repair, one would only hear two exhaust beats per revolution of the driving wheels.  How peculiar.

By setting the cranks at 90^o to each other, the pistons are never at opposite ends of the cylinders and starting is more-or-less assured.  And one gets that lovely 'four beats to the bar' exhaust note - 'Wuff, Wuff, Wuff, Wuff'.  If a 'Black Five' is working a special train down the partly-reopened Waverley Route, it passes within hearing (not in sight, though) of Poppingham Towers and the sound is mightily impressive.  You see, the engine is on the climb to Falahill Summit and the regulator is up in the cab roof.

Note - we are discussing two-cylinder locomotives here.  Others to follow, later.

If the locomotive's cranks are set at 90^o (giving four exhaust beats per revolution of the driving wheels) that's quarter of a circle, isn't it?

If you ever find yourself struggling with the 'quartering' of a model locomotive, you can reassure yourself it's all in a good cause - blind spots, prevention of.

*

Did that make any sense at all?  Probably not.

Next time I'm going to attempt to let you see what the inside of a cylinder looks like.  This will involve us all taking a virtual trip to Yorkshire.


'N' Gauge is Such Fun - but, maybe, not the wheel quartering!

Many thanks for looking and all best wishes.

Cheerie-bye

John

PS Sorry about that 'Wuff, Wuff, Wuff, Wuff' bit - something of a low point I fear.