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BR Standard class 6 No. 72010 'Hengist' and Clan Discussion Thread

Discussion in 'Steam Traction' started by Bulleid Pacific, Nov 23, 2009.

  1. 'Clan' Hengist

    'Clan' Hengist New Member

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    Frame extension view.PNG

    This is a different view of the frame extensions. The view previously provided was partly exploded. The 'shoes' on the frame extensions allow the mounts to move slightly as previously explained.

    Hope this helps.
     
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  2. 'Clan' Hengist

    'Clan' Hengist New Member

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  3. MellishR

    MellishR Part of the furniture Friend

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    While we're discussing these details; why are there frame extensions rather than having the frames extend all the way? I understand why the GWR had extensions in front of their cylinder blocks, but why at the back end of a Standard?
     
  4. northernsteam

    northernsteam New Member

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    No doubt someone else will give the definitive answer, but if I have followed it right it is a very good job they are or we would not have been able to get the frames machined as we have! They would have been too long. Perhaps that is a clue as to why they exist, apart from the need for thicker plates under the cab that is.
     
  5. 'Clan' Hengist

    'Clan' Hengist New Member

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    This one for our technical guru Ian to answer. I am not an engineer, just a humble train driver who is glad not to be at work today. My colleagues are struggling with the aftereffects of the derailment at Sheffield. One through platform and 2 south facing bays. Utter chaos with trains queuing up to get through in both directions. At least no one was injured which is a blessing.
     
  6. Bikermike

    Bikermike Member

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    Because the GW did them at the front?

    I guess joining the frames isn't too bad as the majority of the forces will be in tension, so buckling isn't an issue. If that is the case, you can really make a join at either end, at which point do whatever the GW isn't doing is the right answer.
     
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  7. Jamessquared

    Jamessquared Nat Pres stalwart

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    Looking at the diagram above, the rear frames are set wider than main frames. As a hunch, that probably provides a more stable platform for the cab and firebox. Making them as extension frames is probably easier than creating a joggle in a single-piece frame.

    Tom
     
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  8. std tank

    std tank Member

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    Well, Stanier did exactly the same on the Lizzies and Duchesses. I would say that it was done to enable a wide firebox to be fitted. Also similar on Gresley's A1/3s and A4s.
     
    Last edited: Nov 11, 2020
  9. class8mikado

    class8mikado Well-Known Member

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    Gresley doubled the number of members instead of doubling the thickness, not sure how Bulleid approached it but I bet it was similar to the standard pacifics which might look LMS but here is a lot of Bulleid going on between the wheels.
    At this point in the loco any cross bracing is going to interfere with the ashpan so in the absence of this, making narrow rigid members makes sense.
    Although it was decided that Bar frames were a step too different for the standards surely the next best thing would have been shallower/thicker plates... like the extensions throughout ?
     
    Last edited: Nov 11, 2020
  10. huochemi

    huochemi Well-Known Member Friend

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    Really? I would have thought the braking forces through the trailing frames are potentially significant.

    On a more general point, and ignoring the LNER and most of the LMS Pacifics with their multi-ply rear frames, the Clans, like the Brits, Bulleids and 46256/7 adopted the more globally (i.e. American) accepted design of narrow slabs and a trailing truck (Gresley/the LNER went for a radial axle, presumably to save weight). Even where bar frames were adopted, the rear frames were often separate plates, the rear plates being thinner than the main frames as they don't have big holes in them and are not subject to the forces of piston thrust etc as the main frames are, and there was no point in making them unnecessarily massive. I think the reason rear extensions on plate frame locos are thicker than the main frame plates, is that they are limited in depth and it was probably not practical to massively stay them while giving room for the ashpan etc. The cabs of locos with the narrow rear slab extensions are mounted on the firebox rather than the frames, so for instance, 46256/7 shared three boilers between them as the boilers used by 46220-55 had no provision for mounting the cab.
     
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  11. class8mikado

    class8mikado Well-Known Member

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    Never realised that they were any thing other than the standard pacifics had boiler mounted cabs... you learn a little everday.
     
  12. 242A1

    242A1 Member

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    Having had a look through the Clan Project design page I see a valuable range of improvements. Has anyone looked at the valve gear? Because the design as fitted produces events which are not in accordance with those achieved by best practice.
     
  13. 30854

    30854 Part of the furniture

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    Hadn't heard that mentioned before (regarding the 'Clans') and I'm officially intrigued. Could you expand on your comment a bit please?
     
  14. northernsteam

    northernsteam New Member

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    You should know by now this is the place to learn about all sorts of things, it might not always be right but you still learn!
    I look forward to learning about the motion improvements we could do as well.(no, not us personally, the loco I mean).
     
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  15. class8mikado

    class8mikado Well-Known Member

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    Must admit i read in the beano many moons ago that the Std Locos Valve gear was a somewhat ' Crude' interpretation of Walshaerts, the late Don Ashton commenting that the Std 5 valve gear was not as good as its LMS Predecessor.
    Dont think the ASTT looked at this in particular But Mr Hind definitely has a paternal eye on the project so maybe someone will ask about that.
     
  16. 242A1

    242A1 Member

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    Correct. It was the late Don Ashton who pointed out the limitations of this valve gear arrangement. Have a look at the Don Ashton website, all is revealed. Locomotives built 20 years earlier had a better valve gear design, probably even earlier than that if you look hard enough. The Std Class interpretation and application of Walschaerts' gear was pretty close to the BR notions of exhaust system design.
     
  17. ianh1

    ianh1 Member

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    Apologies, I haven't checked this forum for a while and the automatic notifications seem to have stopped working. Some answers

    What function do the two 'Eyelets'on the top side of the frame extensions fulfil...

    Yes, for lifting. There's 2 more on the front of the frames, we have to rivet the 2 (almost!) circular strengthening plates to the holes. The rear ones are not reinforced but the plates are thicker at the rear compared with the front.

    There are 4 firebox supports. 4 shoes are bolted to lugs that project from the bottom of the foundation ring. These shoes sit on 4 firebox supports and can move on lubricated liners. 2 of the supports are on the Front Firebox Support & Truck Pivot and 2 are on the supports bolted to the frame extensions. The grey component in the image is bolted to the frame, the brown component is bolted to the rear section of the firebox foundation ring. The shoe is constrained left/right but can move fore and aft as the boiler contracts/expands.

    Supports.jpg

    Why frame extensions? I don't know personally but the reasoning on wide fireboxes and ashpans seems to be right. We haven't been able to fit the frame extensions as the assembly would have been too long for the hornblock machining station. These should get fitted in the next few weeks.

    Valve gear. Have a read of section 4 on https://www.theclanproject.org/design/Clan_Design_Clip.php. John Hind is now a very active member of the engineering team and on Monday he was enlightening me on the pros/cons of Walschaerts valve gear vs. Caprotti. We have managed to decipher all of the valve settings from the motion drawing - a visit to the NRM to see the original drawing was of great help.
     
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  18. class8mikado

    class8mikado Well-Known Member

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    Thanks Ian, read it again quite recently - Think the question being asked on the Valve gear is whether the Walschaerts gear off the
    drawing board is what we are getting or, not withstanding the already made support bracket, whether any consideration has been / is going to be given to re examining its geometry, given the computing power/ analytical tools and the work of the likes of Mr Ashton at our disposal today.
    As for me Pro Caprotti, Pro double chimney and Pro 1F tender all the way, and still think the historical justifications for all three are sound but these are at the end of the day' side show' issues...
     
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  19. ianh1

    ianh1 Member

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    John Hind told me today that one of his ASTT gurus had spotted that the Walschaerts valve gear geometry was not ideal. However doing something about it may be difficult. Today we've been doing a lot of frame measuring. Here is Carl from CTL Seal at work today with his Faro Arm

    DSC_0079.jpg
     
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  20. northernsteam

    northernsteam New Member

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    Yes, continuing progress is good to see Ian, especially where caution and accuracy is being exercised. Also good to see some of the many parts which are already to be fitted as work progresses, I mean the handrail knobs. A minor but essential part of the finished locomotive.
     

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