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P2 Locomotive Company and related matters

Discussion in 'Steam Traction' started by class8mikado, Sep 13, 2013.

  1. The Green Howards

    The Green Howards Part of the furniture Friend

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    What I didn't realise until it was mentioned on Saturday was that a P2 was pretty much on the cards right at the beginning back in the 90s but that the A1 was more likely to "work straight out of the box" and so the A1 was chosen.
     
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  2. Kylchap

    Kylchap Member

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    Very nice but I'm not sure about the livery. Is it authentic?
     
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  3. The Green Howards

    The Green Howards Part of the furniture Friend

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    No, because there'll not be any lead in it :D
     
  4. 240P15

    240P15 Well-Known Member

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  5. class8mikado

    class8mikado Well-Known Member

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    Currently pondering this kind of thing with ( Traditional Piano wire / Optical alignment/current equivalents etc) the 'Hengist' build.
    Wonder if that ruler would be worth running over Tornado...
     
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  6. MellishR

    MellishR Part of the furniture Friend

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    I remember reading recently about alignment of one loco being set up by the old stretched wire method, and wondering why they weren't using lasers. I have conveniently forgotten which loco it is, whether a new-build or a preserved one being overhauled.
     
  7. W.Williams

    W.Williams Well-Known Member

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    For all the work and engineering going in to this, why wouldn’t you use the best possible tools available to get the setup as near to perfect as possible.

    Not to take anything away from the old methods, they have proved their worth many times over.
     
  8. RLinkinS

    RLinkinS Member

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    Using lasers is not simply a case of buying in a laser. You also need special fixtures for all the points you are going to measure to. I suspect that using the old methods can be as accurate if particular case is taken. It will take longer but will cost a lot less.
     
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  9. W.Williams

    W.Williams Well-Known Member

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    Did I say it was that simple?

    The old method will never reach the levels of accuracy that modern techniques can.
     
  10. Ploughman

    Ploughman Well-Known Member

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    However
    With more accuracy will tolerances be too tight.
    One of my old tasks at BREL was to run long bolts through a lathe to clean The threads.
    The old lathe was ok for the job and could cope with slightly bent bolts.
    Then they bought a new lathe. The first bolt broke the head.
    Some slack can be a good thing.
     
  11. Steve

    Steve Resident of Nat Pres Friend

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    Not worth the effort for a piece of kit that moves around as much as a steam loco, not to mention changes in temperature from works to working. and where flexibility is fundamental to allow it to go around curves. People may talk in thous and even specify them on drawings but the reality is/was far removed from this. Even at Swindon.
     
  12. W.Williams

    W.Williams Well-Known Member

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    Difference of opinion I guess.

    I believe if you are spending millions and there are better ways then you incorporate them. I believe if you can make it better, then as a professional engineer you are obligated to.

    I believe in doing the best possible engineering to make superior products, I abhor “rough enough” thinking. Maybe fine for the legacy locos, but for a new one, no way!

    Not to mention, poorly fitting parts wear faster.
     
    Last edited: Sep 22, 2018
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  13. 242A1

    242A1 Member

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    At the Ordinary Meeting- October 25th 1955 of the Swindon Engineering Society a paper was delivered titled "The Steam Locomotive: A Machine of Precision". This was the Presidential Address delivered by K. J. Cook to the Institution of Locomotive Engineers that was originally delivered in the September of the same year. Think about that title.

    We are concerned about flexibility, means of getting around curves but this should be incorporated by means of component design, for example controlled lateral movement on driving wheel axles, have a look at the UP system, not exactly rough and ready. Adequately considered running clearances are important particularly when you remember that the machine that you are dealing with has a floating crankshaft. Then you have the coupling rod links to other floating axles and if you think that these remain straight under heavy loading, please do not. And you do have expansion considerations.

    The need to build on solid foundations was well recognised. Frames that flexed, though at one time seen as being useful, became unwanted. Plate frames became more heavily braced, bolts and rivets gave way to welding, bar frames were commonly used but the cast steel bed and its fully welded equivalent became best practice.

    Mechanical refinements and developments that were not used in the UK were found to be invaluable elsewhere. The Franklin self adjusting wedges minimised a cause of fatigue, reduced wear, improved ride comfort and compensated for the effects of axlebox expansion.

    The optical alignment gear used at Doncaster was superior to the Zeiss apparatus and it was obtained by the SVR. The opportunity to have the P2 construction checked by what could be viewed as its modern successor should be grasped with both hands. The importance of accurate initial assembly should not be underestimated.
     
  14. Steve

    Steve Resident of Nat Pres Friend

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    I am very much in agreement that such things as flexibility should be incorporated in the initial design and that there are ways of doing this; bogies for example. However, the plain fact is that the British steam locomotive as we know it and now spend many hours maintaining and operating is not built like this and we have what we have. If we incorporate all we know into the new P2 or any other replica, it would be so unlike the original as to not be a replica but a totally new design. You can get away with some subtle changes for the better and, with some things you can take advantage of finer machining tolerances but, IMHO, the fact remains that they aren't close tolerance machines. They are basically two, three or even four steam hammers hell bent on knocking everything to pieces.
     
  15. huochemi

    huochemi Well-Known Member Friend

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    I am not sure how many of these examples are directly related to dimensional accuracy. Adjustable wedges, as Cox pointed out, have an effect on axle spacing. Lateral motion devices allow increased slop but control it by providing a damping effect to the transverse movement of the axle.
     
  16. W.Williams

    W.Williams Well-Known Member

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    By taking advantage of modern techniques it makes it a totally new design? Incorrect.

    The design intent is still exactly the same, a functioning P2. Some component design intent has changed, roller bearings for example, but this does not change the design of the machine to render it an innacurate representation. That is a tenuous assertion.

    As for “ they aren’t close tolerance machines” I get what you are trying to say, they rattle about, but the actual fact is many of the tolerances on these machines are very fine, and must be designed and manufactured with great care.


    The technology to do it better is available, I’m happy it’s being fully utilised. I have no idea why anyone would propose using old systems when newer better ones are available. Especially when spending millions and millions of pounds. You just wouldn’t!
     
    Last edited: Sep 23, 2018
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  17. class8mikado

    class8mikado Well-Known Member

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    Indeed if spindle x needs a hole x plus 2, no point in saying That's ideal , but it ll be ok to be
    x plus 1 .5 or x plus 2.5 and slightly offcentre...
     
  18. S.A.C. Martin

    S.A.C. Martin Part of the furniture

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    The way it was sold to me was that the A1 would definitely be able to work on the national network. The components suitable for an A1 and a P2 were also a big factor in doing it this way round. I doubt that a P2 would have been as successful if it and Tornado had been swapped. The clear advantages of modern CAD technology and computer simulation have helped shaped the P2 in ways that were not available in the early 1990s.

    It is also - I personally feel - easier to sell the idea of building a 50th member of a successful class than arguing to build a 7th member of a short lived class with lots of potential.
     
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  19. Eightpot

    Eightpot Well-Known Member Friend

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    I have been re-reading the P2 Group's website with particular regard to the fractured crank-axles that they suffered, on at least four (possibly five) occasions, and always behind a wheel, apparently. Ok, it is accepted that the fracture started from a keyway, but what puzzles me is why did they only fracture there? Presumably the other end of the axle also has a keyway where it is pressed into the crank web, too. However, as that end of the axle is smaller that that of the wheel end, why did they not fracture at the smaller diameter end? Thoughts, anyone?
     
  20. W.Williams

    W.Williams Well-Known Member

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    Are they key ways the same at both ends? Is the interference fit the same for the crank web and the wheel?

    These were fatigue failures. Its not the raw torque per say that killed them. Its the combined loading over time and ensuing plastic deformation that weakened them, leading to failures.
    As you can see the crack growth is uniform and progressive until bearing area criticality is reached and tears the whole thing. Classic fatigue.

    Cant say I'm surprised Stonehaven was the location, there is a fairly sharp grade out of there if I'm not mistaken.

    There is also a bit of combined loading going on there with some bending, and plenty of impact loading to boot, which the other end of the axle at the crank web wont be as vulnerable to given its inboard and has some lever arm working in its favor.

    Then there is the keyway itself. No mistake, that is a pretty sharp edge for a highly stressed component. Nowadays with CNC that can be blended out much more neatly. Even then they could have done that, but clearly it wasn't an issue before the P2.

    The new ones have blended keyways, a stress relief groove and are also 0.375" thicker, and made of better steel.

    Gresley wasn't far off the mark with these. They were just very sure footed and exposed a pre-existing weakness the A3 didn't have the adhesion to expose.

    The difference between something passing or failing low cycle fatigue can be a small number and at this time fatigue wasn't fully understood. de Havilland Comet anyone?

    Also, to answer your question, is there not a bit of mechanical double loading going on at this location. In the cycle there will be instances where the peak stress in the axle is at its highest when the piston forces double up. That is to say, the inside engine and outside engine will be working together to produce a torque in the axle that is higher than at any point in the cycle.

    On the inbound side near the web, this is not as acutely felt owing to its position and having mechanical advantage over which stress can dissipate. At the wheel interface end of the axle, there is no escape from the torque coming from an inside and outside engine combined. That would be so typical of conditions that drive a fatigue failure. Peak stresses that are higher than expected and appear only momentarily in the cycle.


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    Last edited: Oct 5, 2018
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