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

[Train Waiting]

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 1


Hello Chums

After wittering on in a post on my Poppingham thread about a locomotive being reboilered with a superheater, it occurred to me that modellers often use terms like this but might not be completely sure what is meant by them.

I wondered if it might be an idea to include a short series on our Fabulous Forum looking at steam locomotives from a 'N' gauge modeller's perspective.  The emphasis will firmly be on conventional British practice.  This means many fascinating experiments, developments and dead ends in steam locomotive engineering will be ignored.  Also, as this is a model railway thread, we'll be looking at steam locomotives from a 'N' gauge modeller's perspective.  Therefore, the analysis will tend towards the superficial.

I hope others, much more knowledgeable than me, will be kind enough to add their thoughts and views by way of discussion.

***

Rocket and Wheels

We need to start somewhere and, as I intend to limit my observations to the conventional 'Stephensonian' locomotive, what better place to start than Robert Stephenson's famous Rocket of 1829.?  You see, the principal arrangement of Rocket continued in mainstream British practice right through to Evening Star.  Or, if you prefer, Tornado.

We all know Rocket – a yellow locomotive with a separate tender.  A horizontal boiler, with a chimney at the front, mounted on wheels.  Driver and fireman together on a footplate behind the boiler.  Remove the adjective 'yellow' and the description could equally apply to Evening Star.  Even on the outside, Rocket set the norm for the steam locomotives that followed for more than 130 years.  And what is in the inside is even more important.




[This picturingham shows Rocket, somewhat altered, in her final condition and her tender is missing.  Not yellow now!]


So, we start with Rocket.  Not the first steam locomotive and not even the first steam locomotive built by a Stephenson.  The investigation of pre-Rocket locomotives is a fascinating subject, more akin to the study of iron dinosaurs than iron horses.

As Rocket is fundamentally a horizontal boiler on wheels, we'll commence with wheels.

Right-o, as you know, Rocket looked like this, Oo – a pair of large diameter wheels at the front and a pair of smaller diameter wheels at the back.  Soon after Rocket, there were oO variants (Robert Stephenson & Co's Planet of 1830).  There were also OO locomotives, an arrangement that was also used on some pre-Rocket locomotives.

Then, in 1833, Robert Stephenson & Co. developed the OO into a OOo for the Leicester & Swannington Railway.  This was followed in 1834 (although construction commenced in 1833) by Patentee, for the Liverpool & Manchester Railway, which had a oOo wheel arrangement.  Again, in 1834, Robert Stephenson & Co built a OOO locomotive for the Leicester & Swannington Railway  Thus was born the six-wheeled 'Stephensonian' locomotive.  Not, of course, the first locomotives to have six wheels, but the first post-Rocket ones to do so.

I have deliberately omitted an important locomotive type here but we'll get to it eventually.

The next development came in 1837, unsurprisingly, from Robert Stephenson & Co, with locomotives of the oOO type for export to France and the USA.  The type entered service in Great Britain on the Great North of England Railway (between York and Darlington) which opened in 1841.

As you will have noticed, differentiating between several variations of four and six wheeled locomotives isn't easy.  And so it remained during the remainder of the Nineteenth Century with descriptions such as 'four wheels coupled passenger engine' in common use.  But, was that locomotive a oOO or a OOo?  Or, indeed, something else?

As time passed and larger locomotives, with more wheels, were making the problems of description even worse, an elegant solution appeared in a magazine article by Frederick M Whyte, published in the USA in 1900.  'Whyte notation' became immediately popular in the English-speaking world, with variations on the concept used in other countries.

Whyte notation counted a locomotive's wheels from the front and the types we have encountered thus far became:

Oo = 0-2-2
oO = 2-2-0
OO = 0-4-0
OOo = 0-4-2
oOo = 2-2-2
OOO = 0-6-0
ooO = 4-2-0
oOO = 2-4-0

Mr Whyte assumed it was normal practice to have little wheels at the front and rear of a locomotive and big wheels in the middle.  The absence of little wheels was indicated by the numeral 0 or naught.  Typically, in spoken English, this is frequently (and confusingly) pronounced like the letter 'O'.  Just like with '0' gauge and '00' gauge model railways.

Here is a practical example of what, when the 'LNWR 18-inch Goods' (commonly called Cauliflower) class was introduced in 1880, was known as a 'six wheels coupled* goods engine'.  And in Whyte notation a 0-6-0.  Much easier!




[No little wheels and six big wheels in the middle makes this Union Mills locomotive a 0-6-0.  Flossie and an interested passenger view proceedings.  Signalman Farmer stands at the bottom of his Lone Star signalbox's stairs.  He's not happy with the equivocal aspect of his Up Starting Signal.  Time to call out a S&T man


More later unless you tell me to stop.

* I'll cover the 'coupled' phenomonen in the next part.

My thanks to our MarvellousModerator @Bealman for his helpful comments on my idea for this series of postingtons and for his advice as to the most appropriate place on our FabulousForum for them to reside.


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Toodle-pip

John

[martyn]

A nicely written starter.

However, it is usually suggested that Stephenson's PLANET was the first 'true' loco as the cylinders were at the front more or less under the smoke box, rather than at the rear.

Look forward to more, and additional posts.

Martyn

[Moonglum]

Please carry on John!

All the very best,

Tim

[SD35]

Please do carry on. 

I intend buying a black 5 to go with a rake of blue and grey mk 1s to cover the Cumbrian Mountain Express in the early 80s.  I've sussed out there's such a thing as rivetted tenders and otherwise but all the gubbins on top of the boiler and the various valve gear types are beyond my ken at the moment so would be handy to learn a bit more before the upcoming Farish release.

I guarantee I'll renumber one to suit 4767 and someone will say, "Pah!  That one never carried a sproghlejack top feed in preservation" or something.

[Chris in Prague]

Excellent, John. Please do continue. I'm sure that I'll learn a lot.

[Graham]

Excellently educational, keep it going please.

[PLD]

I guarantee I'll renumber one to suit 4767 and someone will say, "Pah!  That one never carried a sproghlejack top feed in preservation" or something.

Well as you asked... 4767 is indeed a bad choice to renumber a Farish Black 5... 
It was uniquely fitted with 'Stephenson' valve gear instead of the standard 'Walschaerts' type as modelled by Farish.
(Hence it's preservation naming as "George Stephenson").
To their credit, Farish have recognised many of the main variations on Black 5s including long/short fireboxes, 2 dome positions plus domeless and combined dome & top-feed, welded and riveted tenders, but so far only Walschaerts valve gear, not Stephenson nor Caprotti which all look distinctly different.

[Train Waiting]

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 2


Hello Chums

Before we get to Part 2, thank you very much indeed to your kind response to Part 1 and to @Bealman for giving me the confidence to attempt to write this series.

Please do carry on. 

I intend buying a black 5 to go with a rake of blue and grey mk 1s to cover the Cumbrian Mountain Express in the early 80s.  I've sussed out there's such a thing as rivetted tenders and otherwise but all the gubbins on top of the boiler and the various valve gear types are beyond my ken at the moment so would be handy to learn a bit more before the upcoming Farish release.

I guarantee I'll renumber one to suit 4767 and someone will say, "Pah!  That one never carried a sproghlejack top feed in preservation" or something.

Thank you for this.  As @PLD helpfullty mentioned (4)4767 is a unique and, in my view, excellent engine.  There were 842 'Black Fives' and the class had many variations during its construction spanning the years 1934-1951.  I'm so glad you are interested in this particular locomotive and will make sure I refer to her as often as I can as the series progresses.  She has many interesting features, including her valve gear.
Incidentally, she was built at Crewe during the same month as the LMS 1500hp Co-Co Diesel Electric emerged from Derby works.

**

Frames

In this postington, we will consider locomotives built on a fixed set of frames.  Frames are parallel to a locomotive's wheels.  Which means the frames and the axles connecting the wheels, on each side of a locomotive, are at right angles to each other.

In British practice the method of constructing the frames improved as processes in other industries developed.  Starting with wrought iron, or wood and wrought iron sandwich frames, and ending up with steel plate, the basic concept was unchanged.  Something to hold the wheels in place and to which other parts of the locomotive could be attached.  This resulted in the normal British view that a steam locomotive's identity lies in its frames.

Commencing with Planet, the early Stephenson locomotives had sandwich frames outside of the wheels. This was a common but not universal arrangement at the time and, by 1840, a locomotive could have inside, outside or double frames.  For a time, some locomotive engineers compensated for weaknesses in the materials the frames were manufactured from by having double frames, one set inside the wheels and one set outside.  These locomotives are often mistakenly referred to as having 'outside frames', but double frames is correct. Double frames were especially popular in the 1850-1875 period, although their use steadily declined after 1860 or so.  The concept lingered until the early Twentieth Century, on the Great Western Railway. 

In 1876, what is believed to be the first locomotive with steel plate frames was built in Great Britain.  It was a 2-4-0 of FW Webb's design for the London & North Western Railway (LNWR), and was built at Crewe Works.  Steel plate inside frames became the norm for steam locomotives built for service in Britain.




[Probably the most famous of Mr Webb's 2-4-0 locomotives for the LNWR, Hardwicke of !892.  A later development of the pioneering 1876 locomotive but, fundamentally, similar.  By this time the use of inside steel plate frames was pretty much normal practice.]


The thickness of the steel plate increased slightly over the years.  By the end of volume construction of steam locomotives in Great Britain round about 1 ¼" thickness was normal.  Incidentally, cracked frames was a problem that was unresolved at the end of steam.  If steam locomotive development had continued in Great Britain, it is a distinct possibility that an alternative to steel plate frames would have been used, at least for larger locomotives, as in other countries.

We'll gloss over, for now, the interface between the axles and the frames.  If you'll bear with me, that subject can be put in a box at present.

One final point to make about frames is how far apart they are.  This dimension was important for locomotive designers.  As the first railways were built, there was a variety of track gauges (the distance between the inside face of two parallel rails) in use.  One example is the 5 foot gauge of the Eastern Counties Railway, the first section of which opened in 1839.

There were two main gauges in use in Great Britain, George Stephenson's 'Standard Gauge' of 4' 8 ½" and Isambard Kingdom Brunel's 7' ¼" 'Broad gauge, used by the Great Western Railway and associated companies.  Places where there was a 'break of gauge', most notably Gloucester, became chaotic with passengers and goods having to transfer between standard and broad gauge trains.  The Government became concerned about this and the Board of Trade appointed a Board of Inquiry to look into the matter.  Its report in 1845 resulted in the effective ban on the broad gauge extending northwards.  This was the beginning of the end for the broad gauge and just under fifty years later, it was no more, with all the lines which used it having been converted to standard gauge.

Incidentally, the Eastern Counties Railway had converted to standard gauge in the autumn of 1844.

Although the broad gauge lingered on for almost half-a-century, there wasn't a great deal of locomotive development for it and we shall concentrate on standard gauge from now on.

For locomotive engineers, to provide all the necessary clearances and to allow for the thickness of the frame plates, standard gauge meant that the distance between the insides of the frames of a steam locomotive was about four feet.  This will become jolly important in later postingtons.


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Cheerie-bye

John

[Firstone18]

Do please carry on with this John, I am finding many answers to the many things I didn't know I didn't know!
Very well done!
Cheers

[SD35]

I guarantee I'll renumber one to suit 4767 and someone will say, "Pah!  That one never carried a sproghlejack top feed in preservation" or something.

Well as you asked... 4767 is indeed a bad choice to renumber a Farish Black 5... 
It was uniquely fitted with 'Stephenson' valve gear instead of the standard 'Walschaerts' type as modelled by Farish.
(Hence it's preservation naming as "George Stephenson").
To their credit, Farish have recognised many of the main variations on Black 5s including long/short fireboxes, 2 dome positions plus domeless and combined dome & top-feed, welded and riveted tenders, but so far only Walschaerts valve gear, not Stephenson nor Caprotti which all look distinctly different.

Thanks.  I guess that narrows it down to 5305 or 5407 then unless I go for one of the other classes.  Plenty of options to go at:

https://settlecarlislesteam.co.uk/headboards/cumbrian-mountain-express

[Bigmac]

I guarantee I'll renumber one to suit 4767 and someone will say, "Pah!  That one never carried a sproghlejack top feed in preservation" or something.

Well as you asked... 4767 is indeed a bad choice to renumber a Farish Black 5... 
It was uniquely fitted with 'Stephenson' valve gear instead of the standard 'Walschaerts' type as modelled by Farish.
(Hence it's preservation naming as "George Stephenson").
To their credit, Farish have recognised many of the main variations on Black 5s including long/short fireboxes, 2 dome positions plus domeless and combined dome & top-feed, welded and riveted tenders, but so far only Walschaerts valve gear, not Stephenson nor Caprotti which all look distinctly different.

i wasnt aware of these variations by Farish--please tell us more.

[Train Waiting]

A Coarse Guide to the Steam Locomotive for 'N' Gauge Modellers - Part 3


Driving and Coupled Wheels

The next thing we need to address is the fact that a locomotive is not much use unless at least one axle and its associated pair of wheels is driven or powered in some way.  We'll, hopefully, discuss later how this can be done, but, for now, let's simply assume that, in normal British practice in Queen Victoria's time, one axle would be driven and the wheels stuck on both ends of that axle could be quite big, big-ish, big, or enormous.

Here's that dodgy picturingham of Rocket again.  The powered wheels are the quite big leading wheels and the little wheels at the rear are simply to hold the back of the engine up.  Other than that, they are pretty much just along for the ride.





We now need to stop for a bit and think about a railway where flanged metal wheels run on metal rails, as was pretty much the norm after Rocket.  This results in a very low rolling resistance, but also low adhesion.  The amount of the wheel in contact with the rail is very small indeed.  Much, much smaller than the often-mentioned man's hand contact area between a motor-car's rubber tyre and the road surface.  Victorian locomotive engineers thought that the contact area for a typical driven wheel was about the size of a penny – the proper 'old money' penny.

Which meant that locomotives intended to move heavy, trundling goods trains benefitted from having more driven wheels.  The way to achieve this was simple and went back to the earliest pre-Rocket locomotives.  Drive one axle and connect one or more axles to the driven axle.  This was occasionally done in the very early years by gear-type contraptions, but soon the much simpler device of coupling rods became standard.

The coupling rods were fitted to a crank on the wheels on the driven axle by means of a crankpin.  That way, two, three, four or five wheels (in Great Britain - other countries managed six!) on each side of the locomotive could be coupled together and the number of pennies in contact with the rail increased, to the benefit of adhesion.  Especially in the rain!




[This is a replica of Timothy Hackworth's Sans Pareil, which came second to Rocket at the Liverpool & Manchester Railway's Rainhill Trials in 1829.  She was a 0-4-0 of, at the time, fairly convention design.  Her defeat at Rainhill marked the beginning of the end of the era of Steam Dinosaurs.  You can see the crank, crankpin and coupling rod.  The use of coupled wheels pre-dated the Rocket era.  However,Sans Pareil had 4d's worth of driving wheel-to rail contact and Rocket had only 2d.]


Pedants might say that wheels attached to the driven axle are called driving wheels and the wheels linked to them by means of coupling rods are called coupled wheels.  But 'driving wheels' or, colloquially, 'drivers' is a common description.  Let's not argue about this - especially in the context of model railways where 'driving wheels' is pretty much the normal term employed. But please, please, don't call the coupling rods 'connecting rods' or 'con rods'.  These are a thing, but a very different thing.

Time for another couple of well-dodgy picturinghams.




[A passenger locomotive having two axles coupled by means of coupling rods - 4-4-0 in Whyte notation.  4d worth of driving wheels' contact with the rails.  She also has double frames which makes it difficult to see the diameter of her driving wheels.  On the full-sized locomotive, they are 6' 8½" - big wheels!  Please ignore the front four wheels for now.  That's something for later]


     

[A goods locomotive having all six wheels coupled together by coupling rods to maximise adhesion – 0-6-0 in Whyte notation. A 'tanner's' worth of driving wheels' contact with the rails.  Conventional inside frames, although some very similar locomotives had double frames.  Big-ish wheels - 5' 2" diameter.]


Closing Comments

Writing this sort of thing is dashed tricky and I am aware I have left a few things hanging in the air.  I believe these to be:-

1)  How the axles are attached to the frames;
b)  How at least one of the axles is driven, and
iii) Why the size of the driving wheels is important; including, maybe, something more on the importance of wheel-rail contact.

Please let me know if you think there are others.

Tempting as it is to address these these matters, I'm going to remain on the subject of wheels and frames for now.  They are all, of course, inter-related, but my coarse guide is trying to keep things simple.  Hopefully, you'll join me for the next postington in the series where we will move a bit later in Queen Victoria's reign and think about - oh my giddy aunt - locomotives with more than six wheels.

By the way, a little thought.  In my view, there were two 'long' fifteen year periods where steam locomotive development in Great Britain could be described reasonably as 'revolutionary': 1829-1845 and 1901-1917.  There was also evolutionary progress in other periods as we will, hopefully, see next time.

PS Rocket has quite big driving wheels of 4' 8½" diameter.  Same measurement as the track gauge.  Dashed clever chaps, those Stephensons!


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Cheerie-B

John 

[Moonglum]

Fantastic reading John, can you at some point please define connecting rods/con rods.

All the very best,

Tim

[chrism]

Fantastic reading John, can you at some point please define connecting rods/con rods.

That will come under (b) in the "things left hanging in the air" in John's post

[Invicta Alec]

John,

As you know I have more or less zero interest in steam engines (or at least in the case of model railways I don't) but I have enjoyed reading the first three episodes of your new threadingham.

I look forward to learning. I've already picked up a couple of gems of which I had been hitherto unware.

Alec.