7mm On Heather's Workbench - Prairie ago-go

Discussion in 'WR Action' started by Heather Kay, 8 January 2020.

  1. Heather Kay

    Heather Kay Western Thunderer

    Oh no, not another one!


    I’m afraid so. A 4500 class this time. Hopefully, it’ll be the last steam engine I tackle, and I have to say I am approaching this build with all the anticipation of root canal treatment.

    I want to keep this one simple. We are aiming for a mid-1930s loco, we’ve settled on compensation over springing (the kit is designed for it, apparently), and some electronics will be involved later. Bearing in mind the pratfalls of my last prairie, I hope this one will be the benefit of bitter experience.

    Right, where’s me soldering stick and piercing saw gone?

    Oh, I ought to add I don’t anticipate a blow-by-blow account of this one. You’ve seen me make all the mistakes before! ;)
    Sully, Wagonman, Len Cattley and 13 others like this.
  2. Sandy Harper

    Sandy Harper Western Thunderer

    Good luck with this one Heather. Being from the MM stable it should be ok but watch out for any discrepancies as I suspect it would have originally been drawn for 4mm scale. If this is your last steam loco are you moving into modern image?:)

  3. Heather Kay

    Heather Kay Western Thunderer

    Thanks Sandy!

    Having built a variant on the 4400, the kit holds few fears. I have a feeling the drawings were amended for the 7mm version, although the written instructions weren’t! Still, I know where most of it’s supposed to go.

    I have couple of modern image commissions to deal with, then I’m into about a million coaches. I am going to concentrate on them, as I don’t really enjoy making locos run. Making them look nice is fine, but getting the wiggly bits to work annoys the socks off me. :oops:
  4. simond

    simond Western Thunderer

    Funny, isn’t it? I’d much rather build a loco with its wiggly bits than a coach with all its delicate windows, easily scratched paintwork and plethora of fiddly handles & grabirons, and fundamentally, you need lots more coaches than locos...

    good job we’re all different!

  5. LarryG

    LarryG Western Thunderer

    Each to their own o' course. The time spent making locos run and getting the wiggly bits to work is time that could be spent more profitably on coaches. And they always run first time! :)
    Wagonman, David B, P A D and 3 others like this.
  6. Phil O

    Phil O Western Thunderer


    I look forward to your 45xx build, they're my favourite tank engine. At least you won't be back dating the kit, this time.
    Heather Kay likes this.
  7. Heather Kay

    Heather Kay Western Thunderer


    What with one thing and another, my plan for Thursday of getting the frames up and rolling came to naught. This is where I find myself today, and with luck at least the frames will be erected (without the overlays as yet).

    I admit to not having done compensated chassis before, so I’m being guided by the interweb and common sense. It should work, shouldn’t it? :))
  8. GrahameH

    GrahameH Western Thunderer

    Considering your approach to the last build I feel you will have the confidence to make this one just as good Heather, we all doubt ourselves when we haven't done something before but a steady approach will pay off I'm sure.

  9. Heather Kay

    Heather Kay Western Thunderer


    Well, at least the main frames are together - and square. I opted to use the laminated springs, after a fairly disastrous outing with the JLTRT/MM1 SDK cast ones last time. Besides, one of the castings was broken.

    Perhaps the suspension units will be installed over the weekend.
  10. simond

    simond Western Thunderer

    hi Heather,

    you’ve elected for one fixed axle (it looks like the rear, which makes sense, presuming you will fit the gearbox to it) and therefore the other two axles must be able to rock. That means a single compensation beam on the centreline of the loco. Do not be tempted or misled into fitting a pair of compensation beams, one on each frame, for this way lies folly and madness (ask Pencarrow Chris if you’re in any doubt!).

    The other approach for a 6-coupled chassis is a pair of beams close to the frames for the rear & centre axles (either side of the gearbox), and allow the front axle to rock from side to side, on a central fixed fulcrum. Arguably the elimination of a fixed axle also improves things as the body doesn’t roll from side to side as the rear axle crosses an ‘ump or ‘oller, but it’ll be fine the way you’re going.

  11. Heather Kay

    Heather Kay Western Thunderer

    Thanks Simon! :thumbs:

    The plan is to keep things as simple as possible. To that end, as Malcolm M shows in the instructions, the first version you mentioned is what I shall do. There’s a pair of holes in the main frames, between the leading axles, meant for the fulcrum. The rear axle is fixed and will have the gearbox attached.

    I have actually bodged together the parts for the fulcrum and beam. It just needs me to trap it in the frames with the overlays.

    Pondering is under way regarding how to align all the axleboxes. However, since the bearings are able to move up and down freely, I don’t think setting up is quite as critical as for a sprung set-up. There are some datum points I can use to aid alignment while soldering things in place, so it should be okay - with the aid of the chassis jig to keep things aligned across the frames. Perhaps it might be an idea to solder up the connecting rods before I tackle that.

    Jobs for the weekend, I think.
  12. simond

    simond Western Thunderer

    Good stuff!

    certainly do your rods before your axleboxes.

    I have some springs that fit nicely over my dummy axles and between the hornblocks, which keep them firmly pressed against the frames whilst the initial tack of solder is applied. I normally use a couple of bits of ally angle on a piece of plate glass to keep things aligned horizontally, but as you rightly say, that’s less of a worry for you, you can align the bottom of the hornways with the frames.

    Pix here (though it’s resting on a bit of tile and my crossing jigs :) ) you can see how the rods & springs keep everything in the right place, and the rubber bands mean you don’t need to use your toes or evolve a prehensile tail.

    Second hand Duchess

    One thing to be wary of - make sure the rear axle is absolutely perpendicular to the frames when you solder the bushes in. A long dummy axle (silver steel comes in 13” lengths for some reason) and some squared paper is an easy way to do it.

  13. PeterM

    PeterM Member

    Hi Heather, I am following this with interest as I have the 4mm version in my kit mountain to do. Mine will have to be back-dated though as per your last build.
  14. Heather Kay

    Heather Kay Western Thunderer

    Good luck with your build, Peter. The instructions are fairly straightforward for the places where cuts are made. It’s just taking that big leap forward and cutting, knowing it’s not easy going back again!

    Meanwhile, after a stall for various domestic reasons, some progress.


    I’m using the laminated etched motion for this build. While the SDK includes cast connecting rods, matching cast to etch for colours never looks quite right. We will see how we go. By the way, the etched coupling rods hinge in the crankpin. Not ideal, but since only the front pair of axles move in the compensated setup, I’m not overly bothered.

    Thanks to @simond for prompting me about using springs to hold the horn guides in place while fitting things. I found some suitable spiral things that fit between the frames and now live with my chassis jig. I might play with them later.
    Rob Pulham, Phil O, simond and 3 others like this.
  15. Heather Kay

    Heather Kay Western Thunderer


    Well it’s on wheels, and rolls nicely. Sadly, I’ve miscalculated the diameter of the compensation beam. It’s comically shy of the axles even at the top of their stroke! :confused: :))

    Time for lunch, I think.
  16. Heather Kay

    Heather Kay Western Thunderer


    Well, it rolls. I’ve beefed up the compensation beam gubbins, and it seems to behave as expected. I’m not quite sure what I expected, if I’m honest.

    The next job, then, is sort out current collection and fit the frame overlays. Why do I find I’m not in the mood for those right now?
  17. Richard

    Richard Active Member

    You are much more meticulous than I.

    Being rather lazy,I'd just have bent the compensation beam down at both ends to get contact with the axles.

    Then I'd have spent even more time building a new beam when the results of my craftsmanship created something either totally misshapen or snapped in half!
  18. Heather Kay

    Heather Kay Western Thunderer


    I used brass tube. It wouldn’t have bent without collapsing, but I like your thinking.
    Richard likes this.
  19. Ian@StEnochs

    Ian@StEnochs Western Thunderer


    Just solder a bit of packing between the tube and the axle! It will be quite simple to add tinned shims until the correct ride height is achieved, then the application of the iron should make them one. An added benefit is that you will create a much better bearing surface than the edge of the tube.

    Slip a little bit of aluminium kitchen foil on the bottom if you are afraid of soldering to the axle.

  20. Heather Kay

    Heather Kay Western Thunderer


    Baby steps. I set myself the task of permanently attaching the bearings and fitting the frame overlays. I remembered to trap the compensation beam before attaching the overlays! Some very slight binding with the coupling rods on, but I haven’t sorted out sideplay yet so that is to be expected.

    Happy with that. I suppose making up the cylinders and seeing if the gearbox fits will be next.
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