Nick Dunhill's workbench CR 0-4-4T Wrexham Tanks

Discussion in 'Area 51' started by Nick Dunhill, 3 April 2020.

  1. Nick Dunhill

    Nick Dunhill Western Thunderer

    The new project is to build a couple of these rare Nasmyth-Wilson 0-4-4T Cambrian Railway locomotives. I believe they were colloquially known as Wrexham Tanks. The build is going to utilise a set of Redcraft body etches that I'm guessing have been blown up from OO gauge and are designed to fit an RTR chassis. I have commissioned some etches for the chassis though, and the build will feature working motion and all the BAW. I hope to get around the problem of mounting all the motion and a gearbox on the same axle, which is always an issue on a 0-4-4T.

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    The frames and stays have been prepared, and I have spent the rest of the afternoon fettling Laurie Griffin's excellent cast Stephenson Link parts. I am going to scratch a pair of motion brackets and make sure the slidebars fit.

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    Last edited: 2 May 2020
  2. Nick Dunhill

    Nick Dunhill Western Thunderer

    ....so the journey continues with the motion bracket and cylinder block. I like to do as much as possible before assembling the chassis. It's easier to open up holes and align them at this stage.

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    This stage of the build becomes a fettle-fest of valve gear castings.

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    More fettling tomorrow and hopefilly I assemble the frames......
     
  3. Scale7JB

    Scale7JB Western Thunderer

    Not too tricky to drive an axle with cranks either side, unless you want to put the eccentrics in as well.. Then you'll need to non-patented Bushell method..

    You'll no doubt need the 'Rover' gearbox from ABC gears as its only 10mm wide if you file down the protruding bearings I seem to recall.

    JB.
     
  4. Steph Dale

    Steph Dale Western Thunderer

    I've got one I can do as a 'special' that's only 5mm wide, that was designed for this sort of job (i.e. the Finney7 LSWR M7).

    Steph
     
  5. Nick Dunhill

    Nick Dunhill Western Thunderer

    I did consider the Bushell method, but I think I'm going to replace one of the crank webs with a gear wheel and drive that with a gear on a lay shaft driven by a conventional worm and drive. The lay shaft will be mounted in bearings attached to the frames, so essentially the Bushell method without having to make extra crank shafts. So sorry no royalty for you.....
     
  6. Scale7JB

    Scale7JB Western Thunderer

    No royalty ever expected.. :))

    Really excited to see how you get on. I vividly remember the conversations on how it was achievable years ago and Peter Hunt who some here will know suggested a chain drive through the boiler, and down through the smokebox into the cylinders . That was always a non-starter I think.

    The geared idea I seem to remember was muted too, but I didn't have enough engineering know how at the time to go down that road.

    JB.
     
  7. Nick Dunhill

    Nick Dunhill Western Thunderer

    .....after a fettle-fest I got to solder the frames up. The commissioned etches went together very nicely (Cheers to Mickoo) and we have a basic chassis with a cylinder block, a motion bracket and all the other structures in the correct places. The slide bars will have to come out to be shortened but all well so far.


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    I think I might build the footplate next.......
     
  8. Nick Dunhill

    Nick Dunhill Western Thunderer

    ...this will give you an idea of what I am trying to achieve as a drive mechanism. The gearbox and motor are bog standard Mashima/Ultrascale-type arrangements. The template for the motor was made assuming the Mashima-type motors would be 1833 or 1826. In fact they're 1833 or 1524 so a bit more room and flexibility on the smaller motor. The smaller motor will be fine for a model of this size.


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    Any thoughts.....?
     
  9. Steph Dale

    Steph Dale Western Thunderer

    One obvious one, Nick,

    If that axle moves in its horn guide, how are you going to keep the gears in mesh and/or support the weight of the motor?

    Steph
     
  10. Nick Dunhill

    Nick Dunhill Western Thunderer

    The crank axle will be rigid with compensation in the front axle only. Should still work....
     
  11. Scale7JB

    Scale7JB Western Thunderer

    In order to maintain the gear mesh will you need a secondary gearbox frame which will be captive by the crank axle, and then a sprung motor mount in both X and Y axis?

    Ignore that, just seen updated post.

    JB.
     
  12. Nick Dunhill

    Nick Dunhill Western Thunderer

    Er yes. The crank axle will be rigid, the layshaft supported in bearings attached to the ashpan and the motor gearbox free suspended on the layshaft. The end of the motor will be supported....somehow.....
     
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  13. Scale7JB

    Scale7JB Western Thunderer

    It may be worth mounting the lay shaft and driven axle in roller bearings?

    Eventually, any wear in the brass bearings may lead to the gears not meshing properly.

    JB.
     
    Nick Dunhill likes this.
  14. Steph Dale

    Steph Dale Western Thunderer

    Jon,
    I like the idea of using ball-races in that kind of application, as you know. The problem is that they need fitting to something, whereas I can see that Nick could just adjust the gear mesh and then solder in plain bearings. That sounds much simpler to me.

    Nick,
    Small tip; go for an even number of teeth on one of the gears and an odd number on the other; that will help enormously to even out gear wear.

    Steph
     
    simond, Isambarduk, Genghis and 3 others like this.
  15. Isambarduk

    Isambarduk Western Thunderer

    So, on
    Are you able to recommend a suitable supplier, Steph - or anybody?

    I think they're going have to be made and, as the ratio is to be 1:1, it will be simpler to gash/cut all four wheel blanks on the same mandrel at the same setting.

    To be honest, I do believe that, in this application, gear wear is not going to be woth worrying about (ditto the ball bearings but they are just so satisfying :)

    David
     
  16. simond

    simond Western Thunderer

    If I've understood correctly, the plan is to use the worm wheel as an idler, or is it to have a second gear on the layshaft that engages with that on the axle?

    If the former, then the gear on the axle will have to be the opposite helix to the worm wheel.

    If the latter, then they don't have to be the same diameter as the worm wheel, which might offer options.

    Muffett gears, Tunbridge Wells?

    What about a delrin chain from layshaft to axle?

    atb
    Simon
     
  17. Scale7JB

    Scale7JB Western Thunderer

    I wouldn't have thought there would be space for a Delrin chain on the axle if it's to have cranks and eccentrics.

    JB.
     
  18. simond

    simond Western Thunderer

    ah, yes, good point...
     
  19. Isambarduk

    Isambarduk Western Thunderer

    Thanks for the suggestion of Muffett Gears, Simon ... could be a bit expensive, I fear, to have them commisioned ... was hoping for a supplier such as Ultrascale who have off the shelf products (but Ultrascale do not have anything large enough ~22mm dia) ... should check with Muffett, though, before embarking on in-house cutting.
    But there isn't anything like enough room :-(
    Yes, and outside the gearbox at that.

    David
     
  20. Peter Cross

    Peter Cross Western Thunderer

    Roxey have heard marked left and right in their gearboxes. I presume the gears are Markits.