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

[Bealman]

And a heartfelt thank you from this little Durham lad in self-imposed exile in the Antipodes. A wonderful series and a valuable addition to the forum.

Thank you!

[cmason]

John,

I must add my thanks for this truly wonderful series. I have looked forward to each new "episode" and learnt so much - what I wonder comes next?

(one also is also left to consider if there is a simple way to extract all the page posts in sequence to create a single document which would then make a wonderful mini book to have on hand as a reference work).

BTW - I am now trying to explore the technical details of the last Chinese steam mainline locomotives which ran mainline expresses on the Jitiong railway until 2005, the QJ class LINK as I would like to know how many of the innovations you have described were included in these engines (I recently purchased an N gauge model of one which I have posted pics of elsewhere on our wonderful forum which set me on this path).

Colin.

[Firstone18]

I've created a document from all of the wonderful parts of John's series. I don't think I'll print it though, there are 307 pages! What a super effort and such an interesting and informative series.
Cheers! 

[Train Waiting]

Thank You


Hello Chums

Thank you very much indeed for all those nice things you said about the amazingly brief mini-series. It was especially kind of you. But, I fear you might have encouraged me. I left a lot out of the mini-series - @port perran mentioned an example - the Kylchap exhaust saga for No. 71000. I'm wondering about perhaps posting some 'Occasional Specials' covering specific matters that were either left out of the mini-series or glossed over.

@Cols made a helpful suggestion:-

So... Is that the lot???
[...]
However, I was hoping that the work of Sam Ell at Swindon, and the fitting of double chimneys to all of the "Kings" and many of the "Castles", would feature within your excellent "mini series"... But this is not a whinge. [...]

I almost included these engines in the final section but it was already threatening to be overlong (which it proved to be). Such a postington, or, series of postingtons, might usefully cover some of the other improvements made to these splendid 4-6-0s in their last decade in BR service.

So, that might not be the lot after all - there is an emerging possibility the astoundingly brief mini-series could continue in a slightly modified form. If it does, I promise I'll continue with the SuperSilly, irreverent writing style. Anyone wanting textbook-style can get themselves a textbook.

I even have an idea an idea for the first new postington and it won't involve much work. But first, I'll need to consult our SussexSage and Bluebell Railway correspondent - Floreat vapor!

Thanks, again, for all your kindness.


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Au reservoir for now

John

[chrism]

Did you cover the "ancillary" parts, like injectors, ejectors (other than the Geisl one which is for a different purpose) and braking systems?

[Papyrus]

But first, I'll need to consult our SussexSage and Bluebell Railway correspondent - Floreat vapor!

John

I've been called a lot of things in my time, but 'sage' is not a description that has frequently been applied to me!

  

Cheers,

Chris

[Firstone18]

John, I do hope you can post some more!!
I can say every part of you series provided me with knowledge which was new and I am now looking forward to some extra 'special editions, in the future.
BW
Firstone18

[fisherman]

def MORE  MORE  MORE''


please

such an informative set of postings !

TY

[Bealman]

Looking forward to it, John.  

[Newportnobby]

But first, I'll need to consult our SussexSage and Bluebell Railway correspondent - Floreat vapor!

John

I've been called a lot of things in my time, but 'sage' is not a description that has frequently been applied to me!

  

Cheers,

Chris

It's what comes of knowing yer onions

[Bealman]

I am sure that the esteemed author of this thread (yes, that's you, John) will be pleased to hear that Scotland have qualified for the World Cup for the first time since 1998 

[Cols]

When CHRISM mentioned "ancillary parts" such as ejectors, he did me a big favour as I misread the word "ejectors" as "injectors", which jogged my memory, and I immediately picked up the phone and booked a 'flu jab...!
The Forum's a wonderful thing in quite unexpected ways...!

[Train Waiting]

Boiler Work


Hello Chums

I'm fortunate enough to be acquainted with BR '4MT' 2-6-4T No. 80135, a long-time resident of the North Yorkshire Moors Railway. At present she's having a 'Heavy General' repair. Lots 'N' lots of lovely work.

The boiler work is especially important because, as well as providing the power to make the engine go, the boiler's construction, maintenance and management is critical to safety. The thought of a catastrophic boiler failure in a crowded Pickering station is too awful to contemplate.

Which means it's important a new generation of boilersmiths takes over from the diminishing 'old guard' and then pass the skills down through the generations.

Here's a video I really enjoyed. A group of blokes nattering, but so much more. Their work will bring No. 80135 back to life. And an absolutely fabulous way to sit at home, comfortable as can be, and gain an appreciation of what's below the boiler cladding. And how much hard physical work is required to build and maintain a locomotive boiler the old-fashioned way. Which is, normally, the best way.

Here's the video, it's a slow watch but, I think, a worthwhile one:-

'N' Gauge is Such Fun!

Toodle-pip

John

[Hailstone]

that is a lot of work with a huge bill to follow - 6 figures at least. hats off to the MYMR.
the only boiler work I was involved in was retubing 6106 at Didcot and a similar job on a traction engine - all boiler work is hard graft.

Regards,

Alex

[Train Waiting]

It's Maybe Fine in Practice but it Won't Work in Theory


Hello Chums

I'm wondering about perhaps posting some 'Occasional Specials' covering specific matters that were either left out of the mini-series or glossed over.

Sorry for quoting myself - not good form, I know. The long and the short of it is I've now stopped wondering, so let's jolly along with:-


Occasional Special No. 1

Almost all steam locomotives are reciprocating engines of the Stephensonian type. With two, three or four cylinders, according to the designer's preference and the work to be done. We discussed this sort of stuff in the amazingly brief mini-series.

We have eminent engineers, experienced enginemen and distinguished physicists on our FabulousForum, so I'm going to loup in where the angels fear to tread regarding this topic.

Please think of a reciprocating engine, steam or internal combustion, of your choice. This could, for instance, be a Burrell traction engine, a Gardner diesel, a Rolls Royce Merlin or Velocette 'KTT' - it's up to you.

One thing you are likely to find when you take your chosen engine apart is the cylinder and crankshaft centres are in line with each other and they are fixed firmly in relation to each other by some means. Hard luck if you chose a 'Deltic' engine as your example - it has three crankshafts, so that's a lorra, lorra parts you now have on your parlour floor.

The reciprocating bits of the engine make the crankshaft/s birl round 'N' round. Often at a furious rate. I had a 500cc Velocette 'red-lined' at 6,000rpm - 100 revolutions per second. The late (and great) Mike Hailwood's 250cc Honda Six was red-lined at 18,000 rpm. Goodness, gracious me!

Our steam locomotives' coupled wheels don't quite turn at that rate. At 100mph, 6ft 2in driving wheels, as on a 'Britannia' or 'Merchant Navy' 4-6-2, will revolve at 7.5 revolutions per second or 450rpm. A '9F' 2-10-0 with 5ft coupled wheels at 90mph will achieve 8.4 revolutions per second or 504rpm. Although, hearing of this speed being achieved by a '9F' made BR motive power HQ take SuperSwift action to prevent reoccurrences. The mechanical engineering staff probably didn't require laxatives for some time afterwards.

Now to get to the point (at last!). Unlike the engines we thought about earlier, a Stephensonian steam locomotive has an interesting difference. The cylinders and the crank axle (or plain axle for two-cylinder outside-cylinder types) - the steam locomotive's equivalent of a crankshaft - are not fixed in relation to each other. Let's think about this.

Going right back to the era just after the earliest 'steam dinosaurs', steam locomotives were fitted with springs in an attempt to stop them wrecking the track. Having springs was one of the rules for the Rainhill trials, although it is believed Timothy Hackworth's Sans Pareil didn't have them. The combination of its vertical cylinders and a sprung driving axle would have resulted in a locomotive version of a pogo stick. Robert Stephenson quickly lowered the cylinders of the Rocket-type locomotive and succeeding designs to nearer the horizontal to ensure better running.

Let's take a figure for the vertical range of a locomotive's sprung axles of about 1 1/2in. Springs 'softened' with age and use between repairs, so a locomotive ready for overhaul could have a greater vertical movement than a new or just-repaired one.

Of course, our locomotive's cylinders are fixed to the frames and don't move with the sprung wheels. One would think, in theory, the resulting variations between cylinder centre line and crank axle, or driving wheel, centres would be a recipe for disaster. Hideous piston, piston ring and cylinder bore wear at least. A complete seizing-up at worst.

There is another factor to consider. When other motorcycle manufacturers were using rigid frames, or those with primitive vertical plunger rear suspension, Velocette introduced its pivoted fork¹ rear suspension. Pretty much every manufacturer followed suit, although some took their time. The pivoted fork caused the rear wheel to move in an arc under control of springs. That way, the distance between the gearbox sprocket centre and rear hub sprocket centre remained constant. Jolly good engineering, as one would expect from Velocette.

But a steam locomotive's driving wheels don't move in an arc. The axleboxes move vertically in the frames under control of the springs. This means the effective distance between the crank axle, or driving wheel crankpin, and the piston is greater at the points of maximum spring deflection. As the connecting rod and piston rod are of fixed lengths, that means the only way to compensate for movement caused by spring deflection is for the piston to move in the cylinder. One's thoughts turn to the piston being potentially pulled back into the rear of the cylinder and suchlike horrors.

As if that wasn't enough, here's another thing. Remember we mentioned that, in reciprocating engines, we'd expect the cylinder and crankshaft centres to be in line with each other? Common sense and we'd be forgiven for assuming the same always applied to steam locomotives. And our assumption would be ... wrong!

This wasn't always the case and the best examples to demonstrate the point date from Mr Churchward's time on the GWR. On some of his two-cylinder locomotives, the engine centres (a centre line through each cylinder bore) were not the same as the traction centres (a centre line through each coupled axle in succession). The engine centres were 2 1/2in above the traction centres.  Here's a couple of picturinghams which, hopefully, demonstrate this. I had such fun with a straight edge placed along the piston rods to prove this point to myself:-







You'd think this arrangement would be totally daft, but Mr Churchward's locomotives were streets (railway lines?) ahead of contemporary British types. Yes, there was a difference in connecting rod angularity at each half-cycle, but this made no difference to the efficient running of the engine. But how on earth did Mr Churchward compensate for that difference in connecting rod angularity?

Well, back in Robert Stephenson's time (in my view the only British locomotive engineer more distinguished than Mr Churchward) it was evident that there needed to be sufficient clearance allowed between the piston at maximum stroke and the rear end of the cylinder to allow for the movement of the driving wheel crank, or, from Planet's time, crank axle under the action of the springs.

In order to have the engine and traction centres at different azimuths, Mr Churchward simply allowed 1/16in additional rear end clearance for each cylinder.

So there we are, scary biscuits in theory but a practical engineering job which has stood the test of time.

¹ The pivoted fork quickly became known to all but the most pedantic motor-bicyclists as the 'swinging arm'.

One last thing to mention before I say toodle-pip. I continue to be amazed that our MarvllousModerators allow a coarse modeller like wot I am to write this semi-technical stuff. However, you'll be relieved to learn that viewers of this postington were safeguarded from the worst of my SuperSilliness by the kindness of @Hailstone and @martyn in reading my draft and commenting thereon. To you, gentlemen, my greetings and thanks.

Any remaining errors, omissions, inconsistencies or inelegancies are mine and mine alone.


'N' Gauge is Such Fun!

Many thanks for looking and all best wishes.

Toodle-pip

John