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4079 Pendennis Castle

Discussion in 'Steam Traction' started by Davo, Mar 25, 2019.

  1. bluetrain

    bluetrain Member

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    Thank-you. Your post provides a good succinct summary of present-day issues around gauging.

    The arrival of high square-topped containers has added a new factor into the mix of considerations, but some of the other factors have been lurking for a long time. Back in the mid-19th century, early railway platforms in Britain seem to have been about 18-21 inches above rail level, roughly aligning with the lower foot-boards seen on Victorian-era railway carriages. It must have been very difficult for many passengers to clamber up from those low platforms into their compartments. Unsurprisingly, railway companies came under pressure to raise platforms, which duly crept up in subsequent decades until they reached a height of around 2ft 9in to 3ft above rail level, which remained the standard for most of the 20th century. In recent years, accessibility requirements have seen platforms resume their upward drift.

    The platform raising during the latter 19th century occurred during a period when the majority of Britain's railways were dominated by locomotives with inside cylinders. It does appear that the platform raising on some lines encroached into spaces where later loco designers wanted to place large outside cylinders. ES Cox wrote that, when the LMS was planning new outside-cylinder classes, there were particular problems with platform clearances at some locations on the LNW and Midland sections.

    Platform top-edge clearances on the GWR seem to have been a little less restrictive than on some other lines, and Churchward was able to make the design choice for his outside-cylinder classes to have their cylinders horizontal, low-slung and widely-spaced. On the 4-cylinder classes, the cylinder spacing had to be wide enough to allow for sideways movement from the adjacent bogie wheels. The result is that, not only are the GWR outside cylinder classes wider over cylinders than the majority of comparable engines from the other railways in Britain, but the point of maximum width tends to be at a lower height and more likely to come close to station platform edges.
     

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  2. Sidmouth

    Sidmouth Part of the furniture Staff Member Moderator

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    limited work so far , maybe I accept by choice and split with VT and WC
     
  3. Sidmouth

    Sidmouth Part of the furniture Staff Member Moderator

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    bringing topic back to 4079 , I do wonder if it is to have a main line future a tie up with Vintage trains or WCRC is I suspect going to be needed . The Didcot Stratford corridor remains ideal along with circulars via Sapperton Birmingham and back
     
  4. Johnb

    Johnb Resident of Nat Pres

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    So is Clan Line and life for the single engine owned and maintained by volunteers gets progressively harder and the their days are probably numbered. Clan Line, with it’s regular prestige Belmond working is in the best position and being London based has a large catchment area to recruit volunteers. Bahamas had lottery funding for its last overhaul but that won’t happen again. The K1 can rely on regular Jacobite work but how long will that carry on?
     
    Last edited: Dec 8, 2019
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  5. ruddingtonrsh56

    ruddingtonrsh56 Member

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    I'd imagine the Jacobite is probably one of the most secure mainline steam operations out there. There isn't competition for paths, the route is not a candidate for electrification, it's a route that's popular with rail enthusiasts and Joe Public tourists alike (thanks to thinks like the 'Harry Potter Viaduct') and I'm sure that at one stage it was the income gained from Jacobite operations that was keeping the Fort William - Mallaig line open! If that is still the case then I think if WCRC considered pulling the plug on it Network Rail might try and convince them otherwise!
    As for the K1, while WCRC does have enough Black 5s on its books to run the service without the mogul, the uniqueness of the K1 and its associations with the West Highland line mean emotively there's a real case for it, so I thing NELPG will look to keep it on the mainline as much as they can, it's probably their flagship loco at the moment, and WCRC may well try and encourage them to do it so they can send a Black 5 elsewhere. Although mainline retirement for the K1 would probably see it having the NYMR as its home base which would probably stretch it almost as much as a day on the Jacobite!
     
  6. Johnb

    Johnb Resident of Nat Pres

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    I don’t think emotion comes into it, if WC want to substitute one of their own locomotives as the third engine on the Jacobite roster to save paying steaming fees to a third party, then they will do it. The only thing that may stop them is the fact that a season the Mallaig road knocks hell out to the engines.
     
  7. 45581

    45581 Member

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    And they would have to find a support crew.........
     
  8. Johnb

    Johnb Resident of Nat Pres

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    WC are a TOC with their own staff
     
  9. Pete Thornhill

    Pete Thornhill Well-Known Member Staff Member Moderator

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    I’d say there is more chance of Clan Line continuing on the mainline than say the SVR making a mainline comeback. However this is not a certainty and time will tell and answer the question of how much longer. Increasingly even a owning group going mainline is less and less so definitely a point worth making.
     
  10. Matt37401

    Matt37401 Part of the furniture

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    So anyhow back to 4079...
     
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  11. Pete Thornhill

    Pete Thornhill Well-Known Member Staff Member Moderator

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    Haha yes we must get back on topic, I must admit I thought I was posting in a different thread so do apologise!!!
     
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  12. MellishR

    MellishR Part of the furniture Friend

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    I have trouble grasping how a designer has much latitude in choosing cylinder spacing. Working outwards from the frames you have the wheels, the coupling rods and the connecting rods, all of which presumably have fairly similar thicknesses regardless of the loco class. You can presumably design the crossheads to have the piston rods and the connecting rods not exactly in line, but surely not far out.
     
  13. bluetrain

    bluetrain Member

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    There is actually quite a lot of variation. Looking only at locos with outside cylinders but inside frames, many outside cylinder 2-4-0s and 4-4-0s had connecting rods placed inside the coupling rods, which brings the cylinders closer together. For example, the Midland Compound had large 21-in outside cylinders, but was only 8ft 6½in overall width.

    Among the larger outside-cylinder British locos with connecting rods outside the coupling rods, the cylinder spacing was usually around 6ft 8in. In some cases, for example the Urie 4-6-0s and Robinson 2-8-0s, the frames were inset at the front end, which helped to enable cylinder centres to be kept within that figure and wide cylinders to be accommodated within the loading gauge.

    As you say, the coupling and connecting rods will need to be a certain size, but the designer will likely have some leeway over the space between them. I believe that the cylinder spacing was 6ft 10in on the GWR 2-cylinder classes (and higher on the 4-cyl). The difference from 6ft 8in might not sound much, but is enough to mean greater route restrictions for Castles and Halls, as compared for instance with LMS Jubilees and Black Fives.
     
  14. Jimc

    Jimc Part of the furniture

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    Fractions of an inch add up though. And to get the same area on the bearing you can either make it wider or larger diameter. On the GW 4 cylinder locomotives inside big ends were notably narrower and larger diameter than outside for instance. There's also the question of throw on curves. Its not just the headline static width that matters.
     
  15. misspentyouth62

    misspentyouth62 Member

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    With outside cylinders, surely the critical spacing is that between the coupling rod/crankpin boss on the front driving wheels and the connecting rod that passes? I can't imagine therefore that machining & moving of cylinders inwards gives very much saving? Then there is the subject of bogie wheel clearances.
    Please forgive my lack of big-railway engineering experience here since I'm using my thinking from 4mm scratch building in 18.83 as my prompt..
     
  16. fergusmacg

    fergusmacg Part of the furniture

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    Don't forget the swing (not the right term but will do) of the loco - on a corner the wheels, rods etc are following the rails however cylinders will be at the extremity of that envelope and are the thing you have to consider as they are as made as wide as possible (within the loading gauge) to maximize traction.
     
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  17. Jimc

    Jimc Part of the furniture

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    Throw on curves spectacularly exaggerated... Note how the front of the locomotive (green) projects the most on small radius curves (blue), and the cylinders (red) on larger radius (orange). And yes, bogie wheel clearances are very important.

    throw.jpg
     
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  18. misspentyouth62

    misspentyouth62 Member

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    Absolutely - these things are probably very apparent in scale 4mm since the wheel tyres are also conducting 12v. I currently have a 4MT standard tank on my workbench in 18.83 and I'd hate to have to take anything off the backs of the cylinders for width clearance as there's hardly a fag-paper between the coupling rod boss and conn rods as it is :)
     
  19. misspentyouth62

    misspentyouth62 Member

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    Indeed so - in modelling terms I would term this wheel/axle lateral drift within the frames

    Keeping on topic for 4079, I've just checked my scale four rendition of 5034 Corfe Castle and the rear bogie wheel and cylinder backs are already very close!
     
  20. Jimc

    Jimc Part of the furniture

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    Unsurprised. Holcroft notes that the Bear was limited on cylinder size because of bogie wheel clearance, and the Castles had bigger cylinders.
     

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