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?
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  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.


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  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.


  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.
    AdeMoore and Len Cattley like 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.
  11. Dave Holt

    Dave Holt Western Thunderer

    The reverser linkage and shaft for the inside valve gear has been fitted, as have the bogie mounting spacer and ash pan sides. The bogie mount has had to be altered to give clearance for the inside cross head and drop link. The ash pan sides are replacement for the kit items because 46109 had a rocking grate and hopper ash pan in the period being modelled, whereas the kit items represent the earlier type of pan.
    Inside reverser arrangements:


    Hopper ash pan:

    Might be coupling rods next.
  12. Dave Holt

    Dave Holt Western Thunderer

    Well, it turned out not to be the coupling rods next. I decided to assemble the MJT gearbox conversion instead. The replacement sides were tried in place using the brass rod originally used to align the inside cylinder as it was the right size for the frames and the gearbox sides, prior to fitting the axle bushes. The trial fit showed that a small notch was required on the lower sloping edge of the sides in order to clear a keeper plate cross-beam with axle in its lowest position on the suspension.
    Here is the new gearbox set up with the original Escap RG4 side for comparison and also end on with the gears in place.


    And here with the gearbox/motor in roughly the right position in the frames. A torque reaction link will engage in the new, hollow gearbox spacer at the top, front of the box. This latter feature is a replacement as I misplaced one of the original solid pillars. I was cursing initially and then realised the benefits of a hollow replacement.

    Perhaps it really will be the coupling rods next?
    I've been taking measurements of the width over wheel bosses, cylinder centres, etc., to determine thicknesses of rod bosses and spacer washers and am happy with my scheme. Previous experience with a part built by someone else) Scot chassis showed there could be significant clearance issues, so I had the driving wheel bosses machined to the scale standout and the axles shortened accordingly. Seems to be paying dividends.
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  13. Dave Holt

    Dave Holt Western Thunderer

    Well, I have finally got round to making up the coupling rods - and the connecting rods, too. I've also been working on the crankshaft and eccentric. The former is in final assembly stage whilst the latter is ready to fit once the crank is finished.
    Here are the rods and eccentric. The eccentric is seen from the side which fits against the RH crank webb. The connecting rods are not from the Scot kit because I don't like the shape - to wide at the boss and too narrow at the small end, in my view. These are modified from some spare Black 5 etches.
    Axle boxes and horn guides next.
  14. Dave Holt

    Dave Holt Western Thunderer

    Axleboxes and hornguides have been assembled, matched and suitably marked so they can be kept together when fitted to the chassis. Also, the crankshaft has been built up and the previously shown eccentric attached to the RH web.
    The crank is not the one whose photo started this thread. Sadly, that version met its end in a futile attempt to silver solder the assembly. The replacement has been assembled using a high strength grade of Loctite for the crank pin and slow setting Araldite for the axle. All the joints are pinned after drilling through the webs into the shafts. The eccentric is also pinned to the web. The axle will not be cut between the webs till after the wheels have been pressed on and quartered (or should that be "thirded"?)
  15. dibateg

    dibateg Western Thunderer

    Can you stop it Dave, you are putting 7mm boys to shame! An impressive build.....

  16. Dave Holt

    Dave Holt Western Thunderer

    Thanks, Tony - just plodding along enjoying the challenge I've set myself.
    Hornguides now fixed into the frames.
    Here we see the chassis set up in my Avonside Works jig, with both sets of rods in the extension pins, just for good measure.
    And making extra sure using my extended axles.
    And with the crank axle tried in place.
    Just noticed I've got one on the centre axleboxes in back-to-front.
    Last edited: 2 October 2020
    Deano747, Peter Cross, SECR25 and 3 others like this.
  17. Dave Holt

    Dave Holt Western Thunderer

    Front and rear driving wheel sets have been prepared and temporarily fitted into the chassis.
    Some minor trimming of the crank axle balance weights and the adjacent frame spacer/keeper plate cut-outs is required to ensure nothing catches at the extremes of the axle box travel. Probably, with the loco riding on the springs, these extreme positions would never occur, but best to be safe.


    A bit more work is required before the centre axle can be assembled. One job is to lock the crank pin screws by adding wire stapes along the slot in the head and into the wheel centre, either side.
    The other issue has been caused by a problem with the modified gear box. On inserting the axle and final drive gear, the whole box was found to have a very notchy and gritty action when rotated. I've tried to eliminate this by driving the box with a drill and using very fine grinding paste on the offending gear teeth. This, together with careful use of my engineer's scraper on the teeth has made a vast improvement in running. However, the jaws of the drill chuck have damaged one end of the axle. I've dressed the blemishes out but am wondering whether to replace the axle with a new one, taken from a spare pack, although this will need shortening to suit the thinned wheel bosses. A friend machined the existing axle, but the replacement would have to be done by hand. So, a bit of a dilemma.
    Deano747 likes this.
  18. Dave Holt

    Dave Holt Western Thunderer

    And then there were six.
    Went with the original axle as the two spares I found were too short!
  19. Mike Garwood

    Mike Garwood Western Thunderer


    You're terrible! Have you tried her with the coupling rods on? Come on - spill. Bet she ran smooth as silk. Lovely work.

    Stay safe

    Deano747 likes this.
  20. Dave Holt

    Dave Holt Western Thunderer

    Thanks for your confidence. A bit premature as I haven't started the crank pin bushes, yet. Probably the next task. Adjusting the quartering (120 degrees) will be a matter of trial and error. I used my GW press to put the wheels on, but that give 90 degrees, of course. Tweaking round to roughly 120 is by eye with the front (crank) axle being the master axle.
    I don't expect a successful outcome any time soon.
    Len Cattley and Deano747 like this.