7mm Mickoo's Workbench -WS 72xx - MoK Urie King Arthur - JM LMS Garratt

Discussion in 'Area 51' started by mickoo, 8 September 2018.

  1. SimonT

    SimonT Western Thunderer

    Something along these lines?
    The frame bracket (or whatever it is called) is bolted to the frames. The firebox bracket (or whatever, etc, etc) is bolted/riveted to the firebox. The retaining plate (or .. you get the idea) is bolted to the frame bracket and stops the firebox moving upwards. The firebox slides in/out of the screen.

    No animals were hurt in the colouring of this diagram, but good taste is certainly compromised.
  2. Dog Star

    Dog Star Western Thunderer

    Frame bracket - correct.
    Firebox bracket - correct (note, not rivetted because there are firebox stays hidden by the plate).
    Retaining plate - this and the frame bracket are a single forging.

    No "names" have been changed in this reply, good nature prevails.

    Last edited: 12 April 2021
  3. Max Midnight

    Max Midnight Western Thunderer

    Just say it is 'modern art' then you can get away with anything.
    Project it onto a wall and add sound and you now have an installation.

    Another potential Turner Prize winner methinks. :eek:

    No, it's OK, no need for thanks it's all part of the service. :D
    fenman, Stirling O and oldravendale like this.
  4. SimonT

    SimonT Western Thunderer

    In that case all I need to do is sell a link to it for $650000000000 and job's a good'un!
  5. mickoo

    mickoo Western Thunderer

    Small update on the 72xx, got all the wheels in and pretty much all of the side control sorted, ample for 6' radius curves, too much so on a couple of axles which I'll tweak the number of washers in there to tighten things up.

    Less side control will help with positioning the brake hangers and reducing lateral twisting of the coupling rod joints.

    Had a bit of a fight with the radial truck guides, gave up, went outside and shouted some Viking whilst I chain sawed up a few pallets. Refreshed I returned and decided to go my own way and winged it, turned out well in the end.

    I've added a couple of stops to the top of the radial assembly which limit the full throw and prevent the wheel rim shorting out on the frames. Also added a really simple side control sprung wire which also has a downward component to spring the radial unit.

    I can't see any brake shaft trunnions in the castings either so will need to hunt some of them out or try and 3D print some.



  6. simond

    simond Western Thunderer


    does the wire on the radial not tend to cause it to tilt as it moves sideways?

    I guess if it does, but it stays on, it doesn’t matter!

    Will it do the Peco cross-over? It’s the benchmark for 32mm locos...

    mickoo likes this.
  7. Yorkshire Dave

    Yorkshire Dave Western Thunderer

    One solution is to use a lighter gauge 'V' shaped spring wire with the tops of the 'V' fitting into retainers in swing limit uprights towards the outer edges of the radial truck.
    mickoo likes this.
  8. mickoo

    mickoo Western Thunderer

    Easily, too easy actually, still a lot of side play in the same axles on a 6' curve.

    Regarding tilt, it can, as it can in the Finney models which employ the same technique, I find a bit more weight and a bit more downward force tends to resolve the issue.

    Some one on facebook has concerns about the fulcrum point being so high on the radial truck, I can see that but the extra height when the radial tips causes the fulcrum point to move laterally and thus begins to impart a side control force, as opposed to the pivot point being lower where it will be a near pure rotation point.....if that makes sense.
    Deano747 likes this.
  9. Deano747

    Deano747 Western Thunderer

    Hi Mick

    Nice work, as always.
    I'm assuming it's an ABC unit; which gearbox and ratio have you used please. (Mini?)
    Looks like it'll fit my 42xx as neatly when I get to it.

    Regards, Rob.
  10. simond

    simond Western Thunderer


    my 52 has a 2-stage Crailcrest. This is an easy fit and it’ll pull a house down. It is stupidly heavy.

    Actually, the motor is probably overkill, as all the ABC & Premier motor-gearboxes I've used have been entirely adequate.

    Last edited: 10 April 2021
    Deano747 likes this.
  11. simond

    simond Western Thunderer

    er, yes & no...

    As the radial truck slides sideways, the centering force increases with increasing sideways offset.
    Imagine an identical radial truck but with an identical spring wire fitted through a hole below the axle.
    You would have the same downforce, and the same centering force.

    The tipping moment is the centering force multiplied by the vertical offset between the wire and the flange. It’ll be much less if the wire were fitted below the axle rather than above.

    You can counter the tipping by pressing down harder, but that reduces tractive weight & increases friction.
    Of course, it might be inconvenient or visually unacceptable to have the wire underneath. Dave’s suggestion of two spring wires creates an anti-tipping moment by splitting the centering and downforce and moving them outboard, which will certainly help.

    and if it stays on as it is, it doesn’t matter :)

    interesting about the sideplay. I suspect I made my life difficult by increasing the frame spacing. Did you use Warren’s frame spacers?

    mickoo and Deano747 like this.
  12. mickoo

    mickoo Western Thunderer


    I kept the stock WS spacers for fine scale and yes I could of made wider ones, but, at the time I didn't know how wide I could go. Currently I'm 23.5 over frames, could easily have gone to 25 mm maybe 25.5 mm.

    The radial spring arm is gone, I've played about with the side play on the rear axle and tightened it up so it holds the rear end central on the straight track. Now all I need to is control the vertical motion on the radial which I'll do with a couple of springs.
  13. mickoo

    mickoo Western Thunderer

    Rob, fairly sure it's an ABC in there, no idea of ratio, once it's back out I'll do a rough count by spinning the motor shaft and counting the turns required to move the output gear 1 rev.

    Because I've opted for the stock WS spacers it's a bit tight in the frames between the brass hornblocks and limited side play a lot. In the end I trimmed the bearings down by 0.5 mm or so, don't really like to but needs must as it was a pinch point in the side control measures.
    Deano747 likes this.
  14. mickoo

    mickoo Western Thunderer

    Hello folks, more 72xx I'm afraid.

    Revised the radial springing, should of done it like this in the first place and not taken the lazy mans path.....lesson learned. Basically an upturned wire U over which the springs fit.

    Two tabs on the frames and a bridging piece above with two short sections of brass tube. Simply flip the piece over and make sure the tops of the springs are over the tubes, slip the bridging piece under the tabs and it's all held in place.

    I will secure the bridging piece after paint and I'm sure I have the right spring pressure, but for now it's easy to flip in and out during the build.

    The test run of the resin sand boxes went okay, the sacrificial edge hasn't been cleaned off as a few issues became apparent quite quickly. First, they are scale size, the frame width isn't so they're visually too close together, I will trim their width a mm or so; they'll be scale under width but will visually look better.

    On the bottom the outlet spigot and flange is slightly deformed, I'll probably revise this and make that a separate piece to get them perfect.

    The biggest blunder is the pony truck obscures the outlet, they will need moving outboard, my mistake on the master by not moving the outlet position.

    On the plus side the actuating arm gland plate and filler cap with undercut came out very well, something the old printer could never do, so not all a waste of time.

    Finally the embryonic footplate was bashed up, the frame extensions up front fitted just nicely around the sand boxes, mind there is a small gap to fill where the splasher will be to close up the gap with the frame.

    Hopefully I'll add the splashers tomorrow and begin building up the front end with the raised section over the cylinders and dropped front footplate section.









  15. SimonT

    SimonT Western Thunderer

    you might find some relief for the pony truck by remaking the A frame to the correct shape.
    The other solution is for the frames to be the correct distance apart so that the sandboxes are the correct distance apart;). Ah, the joys of S7:p.
    I haven't managed to get under a 42/72 but this might help from 2815; obviously the outlet is closer to the centreline..
    Front Sandboxes 5.jpg
    Tasty work from the printer.
    BR Tony, Rob Pulham, mickoo and 2 others like this.
  16. mickoo

    mickoo Western Thunderer


    Unfortunately the pony truck is all castings so to make the right shape would essentially be a new rear section from pivot bearing to axle boxes.

    I can bend the current one to make the lower bracket flat but that will kick the whole axle box assembly rearward which would require extension pieces in the short upper struts to compensate.

    The narrow frames were always going to make things difficult, I've just had to compromise on the sand box width to proportion them a little better.

    Nice little detail in the sand pipe bracket mounted to the pony pivot stretcher....which on this engine is a single plank but on the 72xx is a double one (not modelled yet but may be once it really begins to offend me) with the pivot bearing between the two.
    BR Tony, SimonT and Rob Pulham like this.
  17. SimonT

    SimonT Western Thunderer

    Would this be of any use?
    It's a NLTRT one from my 72. I'm developing an alternative with the 28XX A frame but not realistically in your time frame.
    PS Do not assemble it in this orientation:confused:
    3 LINK likes this.
  18. mickoo

    mickoo Western Thunderer

    Took me a while to work out what you'd done wrong :))

    I've re looked at this one....which is actually a Sans Pareil sub kit added to the WS kit.....and all I really need do is flip the A frame arms over. It'll need dissembling as I think the only way to make the new joints strong enough after butchery is to silver solder them....the heat will make them fall apart anyway :D

    On the other hand, if that A frame is going spare I could just swap that bit out ;)
  19. SimonT

    SimonT Western Thunderer

    I'll pop the complete set in the post. Then, you have choice!
    3 LINK likes this.
  20. mickoo

    mickoo Western Thunderer

    Much appreciated darling :thumbs:

    Does the 72xx have that small brace between the arms like the 28xx and this pony casting, or is it missing like yours and the 42xx.