GWR sandwich and double-framed locos

Ah. That's also different from 'marine plywood' (which is what the report was that the Fire Fly replica used), of the kind I've worked with. On looking into this, there are different kinds of 'marine plywood'; the things they all seem to have in common are i) greater care in their manufacture (e.g. no voids, or butt joints in the layers), ii) use of waterproof glues.

Another interesting detail about marine sandwich construction I wasn't aware of. Well, I don't want to derail into marine plywood (although it would be interesting to know why the Fire Fly rebuild decided to use it; I'm guessing it was for increased durability over time; plus to which end-grain oak, I assume, would be somewhat difficult to obtain).

Noel

 

Yes, 'marine' plywood simply concerns glues and gaps. I would imagine convenience and cost are probably the main reasons for the Firefly rebuild ply. I wouldn't be surprised (with absolutely zero evidence) if their frame plates were thicker than the originals too. I don't think it was an industrial archaeology experiment into frame construction. Assembling a suitably large quantity of end grain oak would be a decidedly non trivial task.

 

The London & Birmingham Railway began operation in 1837/8 using 4-wheel Bury bar-framed locomotives. The frames were constructed of "best hammered wrought iron", with the top member of the iron frame being a rectangle of iron bars 4in wide by 1¾in deep. Later 6-wheel Bury engines of the late 1840s had heavier 4¼in by 2¼in frame bars, thickened near the axles and flattened along the firebox sides [Source: RCTS book by Harry Jack].

Bar framing fell out of favour in Britain, but I believe it became normal practice in North America. I don't think the GWR ever had any locos of this type.

 

After a hard day's work Bury retired to the bar. Shortly afterwards the two Great Western engineers came in and he offered to buy them whiskies; Armstrong said he'd have a double but Gooch wanted nothing more than a sandwich.

 

I think bar-frames went the way of sandwiches for the same reason - steel plate became sufficiently good to allow development of plate frames. As to why the UK went plate and the US went bar, presumably it is part of the wider difference in philosophy with more bespoke/craftsman-lead design brought along by the lack of space/axle-load to accept the the less precisely-focused designs used in the US.

Thinking about it, the Gooch Frames are approaching square in section. Which gets tricky if you have standard gauge inside cylinders (the US can just hang ever-bigger cylinders on the outside). If you look at the difference between plate and sandwich, it's the height of the frame which gives you stiffness in that plane (ie sagging/hogging to use a nautical term). That is the most sensible direction to use the material of that element. Side-side and torsional flexs are better dealt with by the frame as a system as a whole (ie including spacers, and critically connection between them). I appreciate this is esoteric (even by NP standards), but does anyone have pics of frame spacers over the age?

If the spacers are just spacers, then a lot of the torsional etc stresses will have to be picked up by the frames (ie the sides), so need to have strength in lots of directions, so need the thickness as well as the depth.

As you get better steel, and more consistent joinings, you can make a box out of the frame and spacers to make a "space frame" - even if it wasn't officially considered as such. (ooooh, there's a thought, imagine a Chapman/Taglioni tubular lattice frame... <goes off for a lie down>)

Meanwhile, in the sandwich shop, Fairlie's attempt to get two different fillings in one piece of bread was popular in the Porthmadoc and Mexico branches, but otherwise not so much...

 

The early GWR standard gauge stock included quite a few bar frame locos of the Bury type (0-4-2 and 2-2-2) acquired from the northern companies, the last one surviving until 1904, as well as a couple of oddities which appeared to have had outside bar frames. Very much later at the grouping a few American built bar frame locos came into stock.

 

Although double plate frames were widely used by most British railway companies during the mid-Victorian era, single plate frames were also in use from an early date. Ahrons draws attention to some 0-6-0 goods engines built in 1848-9 by Sharp Bros for the LNWR & MSLR. These are thought to have been the first to have single inside wrought-iron plate frames made in one piece from front to back buffer beams (with axle guards welded on). The design is thought to have been due to Charles Beyer, then head of Sharp's design department.

After James McConnell had taken over as loco superintendent of the LNWR (S.Div) at Wolverton, he dropped Bury's bar frames and used single inside wrought-iron plate frames for most of the engines that he built during the 1850s. These plate frames were 1-inch thick in the "Bloomers" but only 7/8-inch thick in the "Small Bloomers".

Ahrons also records that steel gradually came into general use in Britain during the 1860s for tyres, axles and motion parts, but only during the 1870s for frames and boilers, with Francis Webb at Crewe being a pioneer in its application. Single frames had been standard at both Wolverton and Crewe well before that time, using wrought iron. But it is possible that the increasing availability of steel influenced other railways and their engineers to abandon double frames, which from the 1870s became generally restricted to the GWR.

 

Improved load-bearing of the p'way (which definitely happened, historically) could also have been a factor. Sandwich beams are lighter, for a given strength - albeit at the 'cost' of being more complex, and likely less durable (because of the decay of the wooden element). So if one were weight restricted in designing a loco (because of p'way limitations), sandwich construction would be a way to ameliorate that. And once the p'way was improved, to handle greater weight...

Mind, this is all supposition, based on not much data; at this distance, the rationales for those changes may no longer be discoverable with certainty. But those old engineers weren't dummies.

Noel

 

If Holcroft's supposition is correct that the last time a set of sandwich frames were renewed was around 1900 it can be assumed that they had a life of at least 30 or 40 years (for instance the Barnum's built in the 1880s must have retained their original frames until withdrawn in the late 1930s) There didn't seem to be much weight difference between GWR 0-6-0s of sandwich or double frames with similar boilers either.

 

I have started going through Backtrack again and have reached the July/August 1992 edition. There is an article by Michael Rutherford ( who is always worth reading ) on the early days of Locomotive Manufacturing. He makes reference to the problem of boiler manufacture due to the available iron plate of suitable thickness being little more than four feet square. He quotes the original 'Planet' boiler needing 22 such plates all having to be hand-riveted with the associated problems of potential steam leakage.

He then goes onto the problems with frames:

''Supply of suitable ironplate also set limits to the quality of the frames of the early 1830's. Stephensons, Tayleur and R&W Hawthorne used sandwich frames in which oak or ash blocks were sandwiched between fairly thin iron plates, often fire-welded to obtain a suitable length. These plates were then riveted together through the woods and horns were riveted on. These frames, which were usually outside, were quite flexible and were used in conjunction with several short, thin inside-plate frames running from the front of the firebox to the cylinders and holding motion brackets and the like.They were intended to keep the 'engine' aligned but did not give any support to the crank axle. No allowance was made for the longitudinal expansion of the boiler at this time ( a further cause of stress ) and frame flexibility caused a number of problems, not the least of which was increased forces applied to crank axles, breakages of which was were an ongoing problem. Once again manufacturing limitations were the main determinants, not until 1843 and the introduction of Nasmyth's steam hammer could suitable cranks be forged satisfactorily. Until that time water-powered tilt hammer was the only machine available.''

Rutherford refers to the issues that manufacturing had in the article from the limitations of the time in materials, machine tools and other manufacturing processes and limitations in the early track.

Edited with thanks to LMS2968: error was mine and not Michael Rutherford's.

 

Steel wasn't used in early boilers; it was around the 1860s that it became feasible following the introduction of the Bessemer process, and better again with the open hearth process. Earlier, frames used wrought iron, as did boilers, but the quality of the iron varied a lot. Much of it was provided by Bedlington Iron, including Timothy Hackworth's San Pareil (they also built the boiler), which was so poor that it leaked like a sieve at the Rainhill Trials. The Stephenson's went for Staffordshire Iron instead, Rocket's four boiler plates were 62 in x 36 in. The frames were flat bar 4 in x 1 in laid horizontally - no wood.
Planet had six main frame, including the outer sandwich ones, the four inners being flat wrought iron plate laid vertically. By Patentee, there were only three frames inside. The cylinders were attached to the inside frames only through the back of the smokebox; they didn't involve the outside frames. The front of firebox was likewise attached, and the drawbar attached to brackets fixed to the rear of the firebox and, again, not the outside frames. This was pushing things too far and Patentee, working hard, pulled the back plate off the firebox, the only locomotive boiler explosion suffered by the Liverpool & Manchester Railway.

 

Many thanks, the reference to steel was my error and not Michael Rutherford's who refers to iron in the article.

 

I recall reading somewhere that bar frames tend to be more forgiving of poor track. If so, perhaps the original lighter track, evidenced in so many photos of early US lines, was a decisive factor, with use of bar sectiln continuing as much out of ingrained habit (s'pose, if feeling more charitable, you could speak of 'accumulated design expertise') until cast frames came along towards the end of steam's reign. So far as the GW is concerned, note too the comparatively light section of the bridge rail employed in IKB's 'baulk road'. In part, at least, might the late survival of sandwich frames on the GW reflect the slightly conservative tendencies of the Swindon D.O, mentioned once or twice elsewhere on our forum?

 

For those interested, the March issue of the Bluebell Times includes an article on The Dukedog, focusing particularly on how they came into being.

See https://www.bluebell-railway.com/bluebell-times/ page 13 onwards.

Thanks particularly to @Jimc for a lot of interesting discussions and help in preparing the article. Any mistakes are mine, not his!

Tom

 

A fascinating read Tom, thanks for that, and for highlighting it.

 

Just for anyone missing steam at the moment - early days of the Dukedog on the Bluebell.



As a little aside - they absolutely hammer through Haywards Heath on the way to the railway, evidently confident in the mainline gauging - or maybe just a mainline crew with little investment in the engine! By contrast the arrival into Sheffield Park platform is very circumspect with much looking over the side to check clearances ...

Tom