4mm Brassmasters Rebuilt Royal Scot, 46109

Discussion in 'Area 51' started by Dave Holt, 18 July 2020.

  1. Dave Holt

    Dave Holt Western Thunderer

    Even the original axle has proved too short but Ill have to live with it. With hind sight, it might have been better to swap the middle and rear axles, but it's too late now as I'm not inclined to take wheels off once fitted.
    The crank pin bushes have been made up and they, together with the coupling rods have been fitted. The wheels go round, after a fashion, but some further work will be required to get smooth rotation. I think 120 degree cranks are intrinsically more difficult to set up than 90 degree. Also, there is some suggestion of a rod centre discrepancy on the front left despite the careful use of the axle setting jigs.
    This loco has a different type of wheel set on the front axle - Stanier pattern bevel rim. with pin between spokes and built up balance weights, compared with the middle and rear sets, which are original plain rim with cast balance weights. Naturally, the Gibson wheels must be from different moulds, so although they are nominally the same diameter and crank throw, there might be some very slight variance between the two types.
    Hopefully, the slight jerkiness can be eliminated by judicious opening of the coupling rod holes, but I don't want it too sloppy to start with.
    Scot_054.JPG

    Scot_055.JPG

    Dave.
     
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  2. Dave Holt

    Dave Holt Western Thunderer

    Not much progress in the last week, partly due to going away for the weekend (Ffestiniog Railway) and partly due to ongoing problems mentioned below.
    Anyway, I now have a proper crank axle, i.e. one without a continuous axle through the middle. The centre section was cut out with care using a piercing saw and the inner web faces filed flush.
    Here it is, seen from the underside, with the inside connecting rod tried in place. All looking very encouraging.
    Scot_056.JPG
    I needed some encouragement as a persistent issue with getting smooth rotation with the rods on was beginning to sap my enthusiasm. A slight tweak of the centre axle thirding and judicious opening of the front crank pin holes seems to have almost got it sorted, creating the will to carry on with the next stages.
    Dave.
     
  3. Dave Holt

    Dave Holt Western Thunderer

    I think I'm entering a minefield! Driving wheel balance weights on Scots appears to be absolutely fraught, with lots of opportunities to get it wrong. The history of the various changes to the appearance of the balance weights is explained, in some detail, in the Wild Swan profile book but even so, it's quite difficult to get ones head round. There were changes to try to solve rough riding with the original locos and then further changes on the rebuilds to suit different coupling rod designs. The Brassmasters kit provides a selection of different balance weight shapes but doesn't quite cover those fitted to 46109 during the period modelled.
    The front (Stanier pattern) axles is reasonably straight forward, being the same as a Jubilee or rebuilt Patriot. This style is not covered by the kit, so some etched weights by Comet have been used. I filed most of the up-stand of the etched rivets off as 46109 appeared to have almost flush rivetted weights.
    The intermediate axle had modified original weights and my initial assumption was that opposite sides would have similar shaped weights, but no, the two sides are subtly different profiles.
    These arrangements are illustrated below.
    First the LH side.
    Scot_057.JPG
    and the RH side.
    Scot_058.JPG
    The rear axle is even more confusing. The LMS wheel balance drawing clearly shows a basic crescent shaped weight with single spoke gap additions, different on the two sides. However, a very good side on photo of the loco clearly shows that the arrangement specified for the LH wheel is actually on the right. I can only surmise that at some stage the rear wheel set was fitted back to front. The, what I now assume to be the LH weight is included in the kit, but the RH will have to be made from a spare centre wheel weight much reduced in size.
    When it's all done, no doubt someone will point out I've got it wrong.
    Dave.
     
  4. Dave Holt

    Dave Holt Western Thunderer

    Here is the trailing wheel-set with the rather different profile balance weights on the two sides, as mentioned previously.
    LH side.
    Scot_059.JPG
    And the RH side.
    Scot_060.JPG
    The crank pin screws have been reduced to length since the photos were taken. The nuts are 16BA opened out to 14BA.
    Dave.
     
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  5. Steph Dale

    Steph Dale Western Thunderer

    Who makes the crankpins Dave? They're rather neat.

    Steph
     
  6. Dave Holt

    Dave Holt Western Thunderer

    Steph,
    The crank pin bushes are modified Ultrascale items. When used with their wheels, the bush inserts into a recess in the wheel boss such that its location does not depend on the 14 BA screw. For use on Gibson wheels, I solder the rear washer to the bush and file flush at the back, to make a top hat bearing. The front bushes are simply shortened to screw up against the back washer.
    All 4 mm scale, of course.
    Dave.
     
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  7. Steph Dale

    Steph Dale Western Thunderer

    Dave,
    Aah yes, that makes sense - is there any reason you've used the Ultrascale ones rather than those produced by Gibson?
    Steph
     
  8. Dave Holt

    Dave Holt Western Thunderer

    Yes, Steph.
    Many years ago, I was advised by a superb modeller (the late John Hayes) that the Ultrascale bushes were a better fit on the 14 BA screws that I use, than Gibson bushes and found it to be so. Ultrascale have the additional benefit of supplying the screwed recessed type which I use extensively, not only for front wheels behind valve gear but also as a flanged mounting for return cranks, speedometer cranks, etc.
    Dave.
     
  9. Dave Holt

    Dave Holt Western Thunderer

    Help and advice needed.
    The Wild Swan profile book includes the Pipe & Rod drawing for the rebuilt locos having the original style ash pan. That drawing carries a note that separate drawing shows modifications required for locos fitted with hopper ash pans. As a minimum, I can see that the large diameter exhaust steam pipe to the injector must have been re-routed to avoid being under the ash pan hopper doors.
    Does anyone have any information about these mods or access to the drawing?
    Dave.
     
  10. Steph Dale

    Steph Dale Western Thunderer

    Dave,

    That, too, makes perfect sense, although it's not something I've noticed. I've just ordered a couple of packs of new Gibson ones this evening to replenish stocks so I'll have a look when they arrive and see what I find.

    Many thanks,

    Steph
     
  11. Dave Holt

    Dave Holt Western Thunderer

    I think I may have solved my pipe routing problem.
    My concern was that the original routing of the exhaust steam supply pipe would interfere with the hopper ash pan doors. However, I've looked at the Pipe & Rod drawings for the Caprotti fitted Black 5's, which also had hopper ash pans, and have established that where the pipe runs alongside the hopper, it is 1'-11/2" from the loco centre line - exactly the same as the standard Scot pipe. So, the normal pipe would presumably be still OK with the hopper ash pan.
    Looking from the side, the pipe bobs up and down like a big dipper to clear the sloping bottom of the ash pan. By chance, this results in the lowest point coinciding with the position of the hopper operating shaft and bracket, so it looks like the exhaust steam pipe would pass under the operating linkage bracket.
    It might not be right, but it would appear that the standard pipe run would still suit a hopper fitted loco. In the absence of better information, I think I'll settle for that.
    Dave.