4mm Brassmasters Rebuilt Royal Scot, 46109

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

  1. Dave Holt

    Dave Holt Western Thunderer

    Thanks, Ade.
    Some progress and a bit of a set-back, today.
    The eccentric rod has been made by modifying the rods from the Brassmasters Fowler 4F valve gear etch. The length has been reduced and a pivoted arrangement provided so the rod can fit over the eccentric sheaves allowing the crank axle to be fitted and removed with the valve gear in place.
    Hinged open:

    Closed, using a brass wire staple:

    The set back is losing one of the slide bar mounting plates - the rectangular one seen in the bottom right in the last photo in the previous post. Extensive searches of the work bench and floor have failed to locate the errant part. It's not something I think I could scratch make, with the four small (1.0 x 0.8 mm) rectangular holes. Fortunately, Brassmasters are able to supply a replacement part etch; so a big thank you to them.
    Con rod next?
  2. Dave Holt

    Dave Holt Western Thunderer

    The eccentric rod, expansion link and radius rod have now been assembled. Nothing accidentally soldered solid for a change!
    Con rod next, perhaps?
    AJC, AdeMoore, simond and 2 others like this.
  3. Dave Holt

    Dave Holt Western Thunderer

    Bullet bitten and con rod created.
    It went from this:
    Two layers of the Brassmasters Fowler 4F rods (their model uses large eccentrics rather than a crank axle to provide some cross head motion), to this:
    Component parts laid out on the jig used to assemble the rod with the correct centres of crank pin and gudgeon pin.
    Rod with big end assembled and later, after some cosmetic improvements, fixed to the cross head, front part of valve gear attached and all placed in the cylinder.


  4. Threadmark: Brassmasters Rebuilt Royal Scot, 46109
    Dave Holt

    Dave Holt Western Thunderer

    Although this is still not my intended next job, some further progress has been made by assembling the frames. You'll notice I've also changed the title of this thread to reflect its new status.
    A few modifications, especially to the keeper plate/springs unit, to accommodate the inside crank and eccentric and the MJT gearbox for the motor, have been required. The reversing shaft and expansion link brackets have been fixed in place. The motion plate is just temporarily sprung into place. It can't be fixed in the frames till after the outside motion bracket has been made up and modified to clear the expansion links.




    Next job is to get the inside cylinder to fit nicely between the frames. I made it to an estimated width, based on measuring loose frame spacers. However, the assembled frames are slightly closer together, so about 0.2 mm per side has to come off the cylinder.
  5. Mike Garwood

    Mike Garwood Western Thunderer

    Fabulous work Dave. I have a question though. Before I start any “add-ons” I usually make up the coupling rods and put the bearings and horn blocks in the chassis. It’s quite noticeable from your chassis that you don’t do this. Would you be kind enough to explain why.

    stay safe

    AdeMoore likes this.
  6. Dave Holt

    Dave Holt Western Thunderer

    I'm not sure what you mean by "add-ons". To my mind, the extra bits I'm fitting to the frames, such as the motion bracket and inside cylinder assembly, are integral to and structural parts of the chassis, so it seems appropriate to fix these before turning to the rods and horn guides. Normally, like you, I build the basic frames and then add the horns using the rods to locate the axle centres.
    On this loco, I'm following the Brassmasters instructions except for making provision for the inside valve gear.
    Also, as you can see, unusually, the kit has the horn guides fitted from the outside, by means of the horse-shoe shaped recesses. The instructions have these fitted after all the frame assembly is complete.
    Another consideration is that the locating holes for the inside lifting link bracket coincides with the edge of the front recesses, the bracket had to be fitted at this stage, before the holes are covered by the horn guide plates.
    AdeMoore likes this.
  7. Dave Holt

    Dave Holt Western Thunderer

    The inside cylinder has been trimmed to fit between the frames, the slide bars fixed to the cylinder and the whole lot trial fitted in the frames. Nothing soldered, yet. A simple jig has been made to help align the cylinder/slide bar assembly with the centre line of the front axle and is seen in situ. This locates in the axle bush holes in the frames. As these will be removed to fit the horn guides, it's another reason the inside bits have to be fitted before the horn guides and rods.


    Brocp, dibateg, michl080 and 3 others like this.
  8. Mike Garwood

    Mike Garwood Western Thunderer

    Thanks for the reply Dave. I get that... so are you using the type of sprung chassis that you used in the Black 5? BTW, love the build so far. You really do put the extra in, which makes your engines so very special. Looking forward to more.

    stay safe

    AdeMoore likes this.
  9. Dave Holt

    Dave Holt Western Thunderer

    Thanks for your interest and kind comments.
    I did promise myself to use fully floating compensation on any future Brassmasters locos rather than springing, but here the inside motion and crank axle preclude a central rocking beam, so I'm using the coil spring arrangements provided in the kit - the same as on the recent Black 5. To be honest, I'm not overly keen on this arrangement as there is not adjustment for axle loading, ride height or level other than by adding ballast in different places. I suppose you could put packers under some of the springs, but I haven't tried that approach so far.
    Len Cattley likes this.
  10. Dave Holt

    Dave Holt Western Thunderer

    Well, I've committed now; the inside cylinder has been fixed into the frames. The motion plate is still loose, but the layer that located the rear ends of the slide bars has been attached to the plate and the central hole opened up to allow the cross head to pass through.
    Prior to fixing, a representation of the cylinder drain cocks and valve chest drain was added to the cylinder. The details of the arrangement are a bit of conjecture on my part although the position and stand-out of the cocks and shape of the discharge pipes are shown on the pipe and rod diagram. It's certainly not the standard arrangement, as used for the outside cylinders.
    Three general shots of the frames. The middle one makes an interesting comparison with a similar view of the 7 mm version recently posted by Oldravendale.



    And a couple, side on, of the drain cock arrangements:


    Since the photos were taken, I also fitted the small cover plates near the front and the firebox/ash pan plates behind the large openings between the centre and rear drivers.
    Lower ash pan sides next.
    oldravendale, Genghis and AJC like this.