GWR sandwich and double-framed locos

Obviously I should like to share your optimism but in the event of catastrophe, large organisational feats might well be irrelevant.

 

I have to confess my first thought on reading the thread title was that we were heading into a discussion regarding GWR catering....

Much like his natural successor Bulleid then really.

I must confess on this topic my knowledge is limited to what I have read, I seem to recall in addition to lubrication matters discussed above the simple idea that Dean was a traditionalist WRT to such matters and thus persevered with the form contributed to their longevity on the GWR. Coincidentally (after a very lovely picture was posted on the GWS Facebook Page) I have been doing some reading around the Aberdare's the last week or so (would make a very pretty new build!), that's a design attributed to Dean dating from c.1900 and is very Dean below the running plate and very Churchward above the running plate.

 

An OVS sandwich would be a triple-decker (largest predicted requirement) made on crisp-bread (modern materials to keep weight down) and involve pickled cabbage (obligatory uncessary oddity)
A Gresley sandwich is made to order from smoked salmon, caviar and lobster
Thompson is standing in the kitchen after Gresley left, looking at a pile of washing up and only stale bread and cheese to work with.
Collet sandwiches are the same as Churchward's with a few slightly different permutations...

Weren't aberdares outside-framed rather than double-framed? But they are very much victorian below the running-plate and Edwardian above

 

After your initial comment I went back and checked some blurb from the Fire Fly Project, which stated that the originals used oak. Now the group did have access to the original plans, but I've been in this game long enough to know that access to original materials is no guarantee of accuracy of reporting.

 

Sorry to go off thread for a sec, are there plans to overhaul her/Iron Duke at some stage?

 

I'm a bit out of touch with things these days, but with Fire Fly there are definitely 'plans', but I don't know to what extent these represent actual plans versus aspirations.

 

It all depends on which direction the forces are in; wood (in general), because of its fibrous nature, is 'anisotropic', i.e. has differing properties when measured in different directions. Plywood is a little more complex, because it contains sheets oriented in different directions.

I don't know the details of the design goals of sandwich frames, but I'm guessing/assuming that it's an attempt to increase strength with less material, much as with modern sandwich-structured composites (as someone mentioned earlier), for weight/cost (more metal will cost more) reasons. The thing is that sandwich composites are also anisotropic - and I don't know which direction they were built to have strength in.

What I do sort of know is that they gain increased 'in plane' (i.e. parallel to the surface) strength by preventing buckling (the primary failure mode for thin sheets loaded in-plane); they do this by separating two thin sheets with an incompressible (in the out-of-plane, i.e. normal to the surface, direction) layer; thereby effectively increasing the thickness.

I would imagine that in loco frames, in-plane strength is a key goal, so the incompressibility of the middle layer is key. Plywood, however, has poor compressibility out-of-plane (a property of the wood it's made from), which is almost certainly why the original design specified end-grain timber. (The particular wood used is much less key than the orientation - because wood is very anisotropic.)

It's interesting to speculate why sandwich construction fell out of use; I suspect it was durability. Over time, the wood would break down (age, as well as decay), weakening the overall structure.

Noel

 

Although Holcroft referred to end grain I do wonder if he meant edge grain, i.e. quarter sawn? End grain is least compressible as a spacer but the wood wouldn't add any strength in itself. Ahrons refered to the use of planks about 3" thick which does suggest an evolution from the earliest wooden framed locos. Perhaps the construction evolved further over the years, Holcroft was seeing frames being assembled for an old "Chancellor" 2-4-0 in about 1900.

 

They did, but it wasn't the sort of plywood you buy from the timber merchant. It was a plywood/balsa/plywood sandwich, so the ply was playing the role of the external plates on the sandwich frame, and the balsa the core. I haven't seen a reference, but I'd assume the core was end grain oriented, as it is when we use balsa as a core material in boat construction.

I'm sure end grain. The description sounds like fitting end grain. Quarter sawn would be so much weaker. The chief requirements of the core are compression and sheer, and it cannot add any useful strength to that provided by the skin.

Yes, its a very hostile environment for wood, especially wood jammed between two steel plates with limited ability to dry out. But sandwich frames must also have been a lot thicker than plate frames to achieve the same strength so space may have been a factor too.

Collett's sandwich would look just like Churchward's, but be much more precisely made with every slice of cheese the exact same thickness.

 

At the risk of continuing this silliness (and please also continue the serious discussion): Wainwright would have taken one of Stirling’s sandwiches, kept the bread but given it a far tastier and more nutritious filling. Maunsell would have found his kitchen preparation budget to devise new sandwich recipes severely curtailed, but would nonetheless have added some special Ashford sauce to a Urie sandwich recipe and thereby made it much better, without anyone being able to say after the fact quite how he did so.

Tom

 

Stanier sandwich - also like Churchwards, with some extra relishes, but his sandwich makers sometimes included peculiar spices his predecessor had favoured which left a nasty aftertaste.

 

As steel improved, I can imagine that the actual load-bearing of the wood ended up (unknowingly) being secondary to the spacing effect, and the strength being derived from a simple plate being replaced by a space-frame construction. When did wood stop being used as a sandwich filler? From what I could read quickly about aberdares, they had double frames, but no wood.

The Robinson sandwich, not terribly original, and made with really thick slices of bread.

The Ivatt (1946) sandwich - like a Stanier but with all the superfluous bread cut off.

 

I have done many miles firing and driving the Dukedog both at home in Sussex and also when it has been away on its holidays.
I can confirm that the frames really do move about a lot. The part over the bogie seems to ride steadily and smoothly and the part over the coupled wheels moves around in a twisting manner. The footplate feels about average from a ride quality point of view, though it has been a while now obviously.
It really is one of my favourites from a footplate point of view, both firing and driving.
I think a Stroudley sandwich would be smaller than the other ones but very satisfying.

 

Given that end-grain wood (i.e. slabs cut horizontally across the trunk) was apparently specified, I'm fairly dubious about both halves of that. End-grain wood has very little strength across the fibers (i.e. along the frames, as apparently installed), which is why it splits so easily; so it would have had very little load-bearing capability. (And one can't get very long pieces in that orientation, anyway.) And specifying use of end-grain indicates that spacing was explicitly its primary intended purpose.

Noel

 

I am assuming that John Chester Craven never made the same sandwich twice and regularly flogged the sandwich makers.

Drummond made a good basic sandwich in his younger day but as sandwiches got bigger it all went downhill.

Webb kept on with the same strange flavours that never worked.

I've also found a rare photo of the sandwiches produced at Derby. As you will notice they are all tiny and have to be doubled up and they are still not doing the job. But very elegant none the less.

 

Firefly being Gooch's rationalisation of North Star, which was basically a Patentee except that the large driving wheels meant the axleboxes came in line with the frames which instead of being straight had to be arched arched over them. The Patentee and Planet frames were clearly straight planks with thin plates bolted either side of them. On these early locos the boilers were as much a structural element as the frames (indeed Patentee's boiler exploded when the backplate of the firebox was pulled off by the drag-pin which was riveted to it when pulling a heavy undivided goods train up an incline). The later GWR renewals and Dean's new sandwich frame locos had additional inside plate frames and boilers independent of them except at the smokebox, no doubt the design had evolved considerably in detail despite their similar appearance to the original Gooch design.

Regarding the rigidity of the baulk road it should be noted Dean used long leaf springs with spacers between the leaves to soften the ride in the vertical plane while Holcroft noted sandwich frames allowed noticeable lateral movement.

 

I’d like to think that in addition, a Stroudley sandwich would contain something described as green, but looking suspiciously like mustard...


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F G Smith put too much filling in his sandwich and had it confiscated for weighing too much.

 

Raven got a new electric sandwich toaster but Gresley wouldn't let him use it.

 

Marsh's sandwiches weren't very good until he put his special sauce in them, then loads of people wanted the special sauce in theirs.
One of Bulleid's sandwiches was meant to be eaten from either end but the filling was all on one side.
Smellie Bogie sandwiches never caught on...