CSBs and the Single Bogie

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Will L
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CSBs and the Single Bogie

Postby Will L » Sat Apr 30, 2011 11:21 pm

Sorry If I’ve been quiet for a while, I’ve had a lot of things to do. One of which has been getting another Loco ready for use on Knutsford East. The subject is an ex GNR C12 4-4-2 tank. As you would expect from me, this loco is fitted with CSB suspension. However the truth is that this wheel arrangement brings us face to face with a few basic issues with the use of CSB’s, and things just aren't as strait forward on this loco, as on othere locos I have discussed to date. The C12 has been on the stocks for a while, but I didn’t really want to talk about it in public until I was reasonably sure I had another proper working example of a CSB fitted loco to pontificate about.

Well I think it is finished now, and it’s going for its first outing on Knutsford at the Liverpool show this week end. While I'm just naturally assuming that it can be relied on to start reliably, run smoothly from a slow crawl on up, and not fall off at random round the layout, it does have to prove:-

1. That it can pull a reasonable load
2. That it will go round the minimum radius curves it will meet on Knutsford.

The second of these isn’t really a CSB related issue. It’s more to do with a slight miscalculation on my part when modelling the injectors. These are mounted prominently under the foot plate behind the cab. I know it wont go round the 3’6” reverse curve on my test track, because the pony truck fowls the injectors which forces both the pony truck and the bogie off the track. Fortunately, the curvature on Knutsford is a bit more generous. So I'm waiting to see if the surgery required to get it along my test track is worth the effort or not.

The first point is CSB related and it’s back to those basic issues hinted at in the first paragraph.

I think it is clear that we have successful methods for applying CSBs to 0-4-0, 0-6-0, 0-8-0 and probably 0-10-0 chassis, and any variant of these where we can happily live with any bogy or pony truck just coming along for the cosmetic ride. Unfortunately the same cannot be said for chassis where non driving wheels will actually have to carry some of the body weight.

We are OK for rigid chassis jobs like a 2-4-0 or a 2-2-2, as you can treat them like an 0-6-0, support the carrying wheels on the CSB, go for a good even weight distribution, and expect haulage powers which are in line with the prototype. There is already a thread relating to 2-4-0 prototypes, and I would be very interested to know how all those E4’s are coming on before I set about mine. However 4-4-0s, (or 0-4-4s and 4-4-2s) really don't run right if they aren’t putting some of their weight onto the bogie, and I don’t believe we have any simple answers as to the best way to do this in a CSB world. (Well that's what I though when I wrote it, we have moved on since then, see theCSB a Question of Gravitythread.)

Clearly this is where getting the C12 to work well comes in, and as I’ve got this far I obviously think I have some sort of solution. I’m just waiting to see if it will pull 5 heavy brass coaches up the 1 in 100 gradient on the down line into Knutsford. I’m wary because I already have a compensated 4-4-0 tender loco which, despite my best efforts, can only do this by dint of a lot of wheel spin. This isn’t seen with great favour by the operating community. The C12 must do better. Our existing C13, same wheel arrangement but in this case compensated, can and does manage this trick, even if it isn’t a totally certain starter. 4 wheel pick up is not enough IMHO.

So the thing I plan to explore in this thread is the various ways that one might implement CSBs on a loco with two driving wheels and a bogie, using the C12 as a, hopefully, successful example. There will be much more to come but, as before, it will be broken down into bite sized, and more easily digestible, chunks. I certainly don't see myself as an "expert" in this area, so I shall be welcoming input from anybody with relevant experience to impart.

Will

P. S. I wrote the above a day or so ago but haven't had time to format the posting. It is now Saturday night and the C12 has spent the day proving it will reliably go anywhere on Knutsford, and yes, starting that heavy weight 5 car rake, and running uphill into Knutsford causes it no problem what so ever.
CSB C12 veiw 2.jpg
CSB C12 veiw 2.jpg (171.01 KiB) Viewed 10926 times

The photographer didn't actually catch the C12 on the up grade. This is the loco I am going to be going on about, probably at some length. It is seen here heading off down hill on the up line in the direction of Manchester.
Last edited by Will L on Mon Mar 31, 2014 12:31 pm, edited 2 times in total.

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John Bateson
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Re: CSBs and the Single Bogie

Postby John Bateson » Sun May 01, 2011 8:42 am

Having recently stated in print that I was a little uncomfortable with CSB solutions for locomotives with bogies etc I look forward to enlightenment and elucidation from what is to come.
John
Slaving away still on GCR stuff ...
Avoiding the soaps ...
http://www.greatcentralmodels.co.uk

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David Thorpe
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Re: CSBs and the Single Bogie

Postby David Thorpe » Sun May 01, 2011 9:06 am

Me too. In spite of the reservations (and perhaps disillusionment) that I've previously expressed about CSBs, I nevertheless went and bought one of Chris Gibbons' jigs at Scalefour North.

DT

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Will L
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Re: CSBs and the Single Bogie

Postby Will L » Tue May 03, 2011 10:49 pm

Recap as to why this is worth worrying about, because I’m sure some of you are already beginning to wonder.

I think experience is showing us that sprung suspension is a good thing. It is a distinct improvement over compensation which was itself a radical improvement over a rigid chassis. Let us not forget that it was the development of practical compensation techniques that made adoption of P4 standards a practical proposition for most of us. Practical springing techniques must be the next step.

While I have no doubts in my mind that a good sprung chassis runs better than a compensated one, before CSB’s, setting up a sprung chassis was more the preserve of the master craftsman than the average modeller. The joy of CSB’s was that once you have the fulcrum points right, balancing out the springing on each wheel is done, and so springing too becomes a practical proposition for anybody who can build a half decent chassis. That is why it is all worth while.

There are limitations, and the big one is that the Centre of Gravity (CofG) of the loco needs to coincide with the centre of the springy beam, and that all the vehicles weight is carried to the wheels via the CSB. It’s true that you could set up the fulcrum points to allow for a CofG which isn’t central, but it isn’t yet a practical proposition because our analytical tools (that spread sheet) aren’t good enough yet. Elsewhere we have seen suggestions that there may be a better way, but we are still waiting on that one. See here. For now we are stuck with the central CofG limitation.

Hence locos with cosmetic bogies and pony trucks are doable now, as are rigid chassis 6 wheelers even if they aren’t all driving wheels. Unfortunately there are other wheel arrangements, so the game is on to extend the concept to those not covered at the moment, and it’s loco’s that really need some of the weight carried on a bogie where we need a solution.

The C12 illustrates the point

The body is a Craftsman kit which has already given some years of service else where. It started on a pretty standard rigid 00 chassis which, in reality, was a 0-4-0 with both pony and bogie along for the ride. This body kit, was an early etched production, and a good one for its time, though perhaps not up to modern Finney-esk standards. The realisation that the Cheshire Lines did have an allocation of C12’s in our period, even if the local engine men didn’t like them much, suggested that this loco would make a useful addition to the Knutsford roster. Better still, having decided that CSB’s were the way to go, there was a Bill Bedford chassis kit available based on springy beams. So a kit was purchased from Bill with a full set of Gibson Wheels and I set about assembling it, without too much consideration of theory or practicability.

The chassis was very nicely designed and etched in nickel silver. It had a number of interesting design features and considerably more fidelity to the prototype than the Craftsman original. I find assembling a well designed etched kit a thoroughly enjoyable experience and I was definitely looking forward to doing this one. There were even three pages of exploded diagrams and notes on construction. Remember this is a Bill Bedford kit. I still think it’s a good kit, but I was in for a disappointment. Having built it in accordance with the instructions, and mounted it beneath the existing body which was already lead filled and really quite heavy, the driving wheels didn’t touch the rails at all. The uncritical, I’ll just put it together as designed, phase was over and I started to think about how it might actually be made to work.

So let’s have a look at the chassis design

The design incorporated springy beams, but they weren’t as continuous as all that. The following schematic shows what I take to be the design intention.

CSB C12 draw 1.jpg
CSB C12 draw 1.jpg (62.97 KiB) Viewed 10795 times

The pair of beams over the driving wheels have their fulcrum point set very nearly symmetrically around the two driving axles. The front and rear fulcrum points for these beams are holes through chassis cross members which also served other purposes. This means that the fulcrum point symmetry wasn’t exact, but it was certainly close enough. The bogie had a second pair of symmetrical beams which had fulcrum points at the centre of the bogie and the extreme ends. To get a beam into the bogie it is mounted under the axles, and the axle boxes bear on the beams very close to the ends. Finally there was a separate pair of springs that supported both sides of the pony truck.

The axle bearing blocks used for the driving and bogie wheels, where interesting. They were just plain rectangular brass blocks, drilled for the correct axle diameter, and running in horn guides bent back from the chassis frame. Small etched tags had to be soldered on to these axle blocks to form their fulcrum points. It is only this connection with the springy beam that keeps the bearing blocks positioned between the horn guides in the frames. This appears to be a perfectly satisfactory arrangement and one that does leave a lot more space on the axle for a gearbox than the HighLevel style of hornblock and guides.

So much for design intentions, with the benefit of 20:20 hind site I could see a few problems

CSB C12 draw 2.jpg
CSB C12 draw 2.jpg (95.82 KiB) Viewed 10795 times

There has clearly been a design change involving the pony truck frame. The etch was different from that shown in the first set of instructions I had for the kit. A more recent version of the instruction, downloaded from Bill’s web site, does match the etches I made up, but, I think the design changes in the pony truck frame needed an associated change in the height of the springy beam it rested on. I can see no sign that this change was made. Here in was a significant part of the problem, making the pony truck wheels about 1mm lower in the frames than they should have been. However I also found a smaller height problem with the bogie, which I suspect was due to the configuration of the beams on the bogie giving significantly less deflection than you might normally expect.

When I first spotted the problem, I did wonder if I’d just got the wrong sized wheels. But no, the Gibson range provides exactly the right size wheels as specified in the RCTS “Locomotives of the LNER” green bible. The kit instructions are silent on this point.

The whole thing typifies the basic problem of implementing a sprung chassis with a number of separate springs. It may well be possible to get it to work, but only with a considerable amount of work getting the various springs adjusted correctly. This is of course a problem we share with the prototype, but without benefit of a weigh bridge to tell you just how much weight you have got on each wheel.

That’s enough for now

Next time I’ll have a go at explaining my thinking on the options for achieving a weight bearing bogie on a CSB chassis, and I will, eventually, tell you how I applied this thinking to the C12.

Trevor Grout
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Re: CSBs and the Single Bogie

Postby Trevor Grout » Wed May 04, 2011 9:08 am

Will,

looking at the bogie drawing, I would expect problems with those outer fulcrum points being so close to the axle centre points.
Now pure speculation on my part I think you may be able to get away without them, the outer fulcrums that is, now it might be possible to fix the centre fulcrum solid and treat each axle in the same way as say Independent springing, similar to a car suspension when leaf springs went out of fashion, just with no shock absorber, that might be an idea, you probably have already considered.

Just me thinking out load, before the trip to the dentists chair

regards
trevor

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Jol Wilkinson
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Re: CSBs and the Single Bogie

Postby Jol Wilkinson » Thu May 05, 2011 7:20 am

I agree that Trevor's idea could provide the answer. It provides what is effectively the same idea as the sprung bogie in several London Road Models kits, which customer feedback indicates does work (even in OO).

The attached shows a simplified version of the assembly drawing from the instructions. It was originally designed for the LNWR Jubilee kit, where the radial truck doesn't have any end cross bearers. There are three small holes in each "leg" of the bogie stretcher to provide alternative positions for the spring wires. The axles run in 2.0mm ID brass tube, which the wire anchors wrap around.


Bogie dwg 2.pdf
(14.14 KiB) Downloaded 506 times


Jol

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dcockling
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Re: CSBs and the Single Bogie

Postby dcockling » Thu May 05, 2011 2:31 pm

The CLAG website shows Ted Scannell's arrangement for the bogie of a 2P 4-4-0, however there is nothing to show how the bogie is attached to the chassis. Is secondary springing required and if so how should it be arranged?

All the Best
Danny

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Will L
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Re: CSBs and the Single Bogie

Postby Will L » Thu May 05, 2011 11:36 pm

Thank you for the feedback gentlemen, welcome as always.

Trevor Grout wrote:..I think you may be able to get away without them, the outer fulcrums that is ..


Yes the same though had occurred to me. However sorting out the bogie design is not really the issue I wanted to chase down. I'm far more interested in how you know how springy the bogie needs to be to balance with the driving wheel springs, and what the relationship between the two of them says about where the CofG of the completed loco needs to be. Get it wrong and the loco will not sit level on the track and haulage power will be distinctly limited (experience suggests).

Following on from that...
dcockling wrote:The CLAG website shows Ted Scannell's arrangement for the bogie of a 2P 4-4-0...


Yes that's classic Ted design, however the C12 has taught me that any sprung 4-4-0 chassis design is not fit for purpose unless it is shown to work under the weight of the body designed to go on it, evidence not posted by Ted on the CLAG web site.

Jol Wilkinson wrote:I agree that Trevor's idea could provide the answer. It provides what is effectively the same idea as the sprung bogie in several London Road Models kits, which customer feedback indicates does work (even in OO).


Like the design Jol, but, as indicated above, no bogie design in isolation will answer the questions I have in mind.

As an aside, I have tried the U shaped self centring spring acting on the bogie pin your drawing shows, but I can never get a spring wire soft enough to actually allow any controlled sideways movement of the bogie. In fact the C12 was designed to have one but my finished chassis runs better without it, that is it doesn't now ping the bogie wheels off on smaller* radius curves. Just how fine does the spring wire of the U have to be for this arrangement to work?

Will
*( bearing in mind that clearances at the pony truck end of the C12 currently limit it to about 4' radius curves).

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Re: CSBs and the Single Bogie

Postby craig_whilding » Fri May 06, 2011 9:36 am

Two methods I can think of -

1 - You count the bearer the bogie is pushing against as an axlebox and attach it to the CSB and provide it with hornguides.

2 - You tap a tube for a screw in one end and a coil spring in the other and allow the height of the bogie to be adjusted finely by the screw but this is still effectively independent of the CSB. The pivot would need to be a tube on the bogie outside of the body tube with the spring in.

The calculation for the first one i'm not sure about though! The latter might be a retrofit to at least allow you to get something working though im not sure if you have a central pivot on the bogie or another system.

Have you asked Bill if there is a mk2 etch at all, I know a club member needed a separate mk2 etch for the L&Y 2-4-2 chassis I think it was that wouldn't work as initially done.

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Jol Wilkinson
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Re: CSBs and the Single Bogie

Postby Jol Wilkinson » Fri May 06, 2011 10:28 am

Will,

I see the LRM sprung bogie as being aimed at keeping the wheels on the track, rather than providing a finite amount of support for the loco (although this may be heresy to some CSB afficianados). Bear in mind that LRM kits are intended to be accessible to builders in all 4mm gauges and who will have some variation in building/assemby skills.

As for the wire size to control sideplay, that' tends to depend on minimum track curvature, how much weight the loco has over the bogie bearing plate, axle spring wire thickness and preload. In other words, how much weight the wheels carry and how much resistance the wheel flanges can offer to side thrust. Clearly, the more weight the bogie axles carry, the more work they can be made to do, but at the expense of weight on the driving axles.

My experience with pony trucks and radial axles has been that, in P4, only very light horizontal springing can work. The smallest guitar strings (.008") are the order of the day, but possibly a softer material (phosphor bronze?) of the same diameter would be better.

Jol

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Re: CSBs and the Single Bogie

Postby Armchair Modeller » Fri May 06, 2011 9:07 pm


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grovenor-2685
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Re: CSBs and the Single Bogie

Postby grovenor-2685 » Fri May 06, 2011 9:43 pm

There is already a Bill Bedford solution?

Quite, which is the main subject of this topic, try reading this post
http://www.scalefour.org/forum/viewtopic.php?f=19&t=1390#p9906
Regards
Keith

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Re: CSBs and the Single Bogie

Postby Trevor Grout » Sat May 07, 2011 4:37 pm

grovenor-2685 wrote:
There is already a Bill Bedford solution?

Quite, which is the main subject of this topic, try reading this post
http://www.scalefour.org/forum/viewtopic.php?f=19&t=1390#p9906
Regards
Keith



and around we go again !

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Re: CSBs and the Single Bogie

Postby Armchair Modeller » Mon May 09, 2011 4:19 pm

Sorry - perhaps I didn't explain myself very well - in the current diagram on Bill Bedford's web site the CSB arrangement seems a little different to that drawn in the original post on this thread - particularly the bogie, where the ends of the springy beam seem to be loose on the BB diagram. I may just have misinterpreted the diagram - if so I apologise profusely.

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Will L
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Re: CSBs and the Single Bogie

Postby Will L » Mon May 09, 2011 4:55 pm

Armchair Modeller wrote:Sorry - perhaps I didn't explain myself very well - in the current diagram on Bill Bedford's web site the CSB arrangement seems a little different to that drawn in the original post on this thread - particularly the bogie, where the ends of the springy beam seem to be loose on the BB diagram.


I noticed that too Richard, but if you look at the image of the etch, also given in Bill's instructions, it has the fulcrum "eyes" etched into the ends of the bogie side frames, and you'd need to fold them up to get the end cross members on. The bogie as etched also has tabs, onto which these end cross members are soldered,which are etched higher than the isomeric drawings suggest. I assumed this is because it would have been impossible to slide the suspension wire into the outer fulcrums points if these tabs were placed as in the isometric diagram. So the diagrams and etch don't agree. My conclusion was that Bill wasn't actually suggestion a single central fulcrum point but had just left the outer fulcrum points off his diagram, but based on things you can really only discover once you've climb out of the armchair. :D

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Re: CSBs and the Single Bogie

Postby Armchair Modeller » Mon May 09, 2011 5:19 pm

Will L wrote:but based on things you can really only discover once you've climb out of the armchair. :D


My armchair is not amused ;)

Seriously, I am actively modelling (even in the armchair on occasions), but had not even thought of building one of these locos until your thread came up. I would have to think very hard for an excuse to have one, even though I like them. Good luck with yours though - and please do keep us up to date with your thoughts and solutions. Even I might need an Atlantic of some description myself, in due course! :)

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Jol Wilkinson
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Re: CSBs and the Single Bogie

Postby Jol Wilkinson » Mon May 09, 2011 8:28 pm

Will L wrote:
Armchair Modeller wrote:Sorry - perhaps I didn't explain myself very well - in the current diagram on Bill Bedford's web site the CSB arrangement seems a little different to that drawn in the original post on this thread - particularly the bogie, where the ends of the springy beam seem to be loose on the BB diagram.


I noticed that too Richard, but if you look at the image of the etch, also given in Bill's instructions, it has the fulcrum "eyes" etched into the ends of the bogie side frames, and you'd need to fold them up to get the end cross members on. The bogie as etched also has tabs, onto which these end cross members are soldered,which are etched higher than the isomeric drawings suggest. I assumed this is because it would have been impossible to slide the suspension wire into the outer fulcrums points if these tabs were placed as in the isometric diagram. So the diagrams and etch don't agree. My conclusion was that Bill wasn't actually suggestion a single central fulcrum point but had just left the outer fulcrum points off his diagram, but based on things you can really only discover once you've climb out of the armchair. :D



Will,

I think it may be a mistake to assume that the instructions and what is supplied in the kit/etch will neccessarily match.

That applies to the BB sprung coach bogie where the instructions apply to the original parts supplied. Some washers are now omitted for a different approach to assembly, but the instructions have not (at least in the packs I bought) been amended, leaving you in the dark.

I took a look at the instructions download but cannot make out what you are supposed to do. The bogie frame on the etch outline (17) does appear to have outer tabs as well as a centre one but the assembly drawing shows the outer ends of the spring wire floating free. I think that the distance from the axle bearing to the outer tabs may be too short to permit sufficient spring flex, but how you are supposed to deal with it isn't clear.

Jol

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Re: CSBs and the Single Bogie

Postby craig_whilding » Tue May 10, 2011 10:30 am

Will have you tried emailing Bill to see what he states is the correct way of building this and possibly also a mail to Ted as well about his 2P?

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Will L
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Re: CSBs and the Single Bogie

Postby Will L » Tue May 10, 2011 11:36 am

craig_whilding wrote:Will have you tried emailing Bill to see what he states is the correct way of building this and possibly also a mail to Ted as well about his 2P?


Thing is I'm not trying to have a go at Bill nor am I terribly concerned about any perceived problems with the kit, some of which may prove to be as much to do with the way I put it together as the kit design. Also if you read back to the top you will be reminded that I didn't start this post until I was happy I now have a good working version of the chassis. So obviously there is more to come on this.

The point I'm trying to bring out is that if you just stick multiple sets of springs under a loco you will get issues with trying to balance the thing out, and with a 4-4-2, or a 4-4-0 for that matter, this isn't an easy situation to avoid. What I'm really interested in is how best to address these issues in general terms rather than in a particular case. This will become clear, I hope, in the next posting but it is proving difficult to find the words I need to finish it.

As for Ted, while he may not be a contribute here, I think you'll find he is a reader.

Will

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Will L
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Re: CSBs and the Single Bogie

Postby Will L » Tue May 10, 2011 3:59 pm

Approaches to a CSB fitted 4-4-0

Apart from the fact that they are easy to build, the great joy when you make a standard, fixed axles only, CSB chassis is that once the design work to get the fulcrums properly placed is done, you can be happy it will work well with no further hassle. It will automatically sit level, and it shares the loco weight evenly across the driving axles so ensuring maximum adhesion. The only post build time adjustments will be to change the CSB wire size, if you want to raise or lower the buffer height, and to weight the loco so the CofG really does sit centrally over the wheelbase.

The problem with 4-4-0 chassis (and 4-4-2’s) is that as soon as you add wheels that carry weight and are not suspended by the CSB, much of this predictability goes out the window. So what I want to address now is how we can produce such a chassis so as to get us back as close as we can to the simple world of the fixed axle only CSB.

Options

As the result of having given this problem a good thinking to, it seemed to me that I had two basic choices.

    1. Find a way to support the bogie wheels from the CSB, hence making the problem of balancing the multiple springs go away.
    2. Find a way of sorting out where the CogG needs to be to compress both sets of springs the right amount. This requires that you have to take into account the relative spring rate of driving wheel and bogie springsIt also means you have to understand what impact shifting the CofG away from dead centre of the springy beam has on the actual weight carried by each axle, bearing in mind we have so far failed to find a way of calculating the impact on weight distribution of moving the CofG in the simple all fixed axles situation. See all 41 posts on the Abstruse CSB Theory thread.

Perhaps surprisingly, I think I have got a couple of solutions to number 2 which I’m planning to share with you shortly, but not in this post which is long enough already. For those of you already gagging at the prospect of more complex mathematics, I’m pleased to be able to tell you that what I have to relate is mostly empirical, and even those with advanced spreadsheet phobia should not be harmed by the explanation.

But why go there when the obvious answer is no1? Well I’m not convinced this isn’t easier said than done, although I do have two “schematic” diagrams of different possible approaches for you. It must be said, that I have yet to see a practical implementation of option 1, and option 2 is a late introduction I added last week when Adrian Prescott produced a running chassis which embodied a possibility I hadn’t taken seriously until then.

Extend the CSB option one
CSB C12 draw opt 1.jpg
CSB C12 draw opt 1.jpg (40.15 KiB) Viewed 10254 times

This makes a 4-4-0 chassis equivalent to a 0-6-0 chassis from a CSB point of view, and fulcrum points are set out using the bogie support point as the “third axle”.

Weight distribution will be exactly as if it was an 0-6-0, one axle worth of weight is shared equally between the bogie wheels.

The complexity of suspending the bogie pivot from the CSB’s is glossed over in this two dimensional slice schematic. The bogie itself can be rigid, or compensated, but cannot have any other springing than the CSB, or it will upset the CSB axle displacement calculations.

The CofG of the loco should be set mid way between the first axle and the bogie fulcrum like any other current CSB design.

This is a purely theoretical suggestion as I haven’t yet come across a bogie design that implements it. The key feature is that the rail to fulcrum point height has to be identical to the equivalent dimension on the driving wheel/axle bock. Given that is has to allow the bogie to pivot and rock, getting the fulcrum to rail height right will not be trivial. That said, I do have ideas as to how to do this, and the next time I start a 4-4-0 chassis from scratch this is the way I plan to go. But, until I have tried my ideas to see if they work as well in practice as they do in my head, I think I will keep quiet about the how.

Extend the CSB option two
CSB C12 draw opt 2.jpg
CSB C12 draw opt 2.jpg (49.14 KiB) Viewed 10254 times


This is a fixed 3 axle CSB chassis with the CofG in the usual place.

Adrian’s basic idea was to treat the back bogie axle as a fixed axle and the front bogie axle as a cosmetic, no weight bearing pony truck. The Chassis he had on show was not, I believe, CSB fitted, but I can’t see any reason why you couldn’t. How easy it is to make the bogie side frames look convincing on the finished model I’m not yet sure. Adrian works quickly, as he does this for a living, so I suspect the fully developed LMS 2P his chassis goes under should be around to inspect in the none to distant future

Next time.

In the next post I will discus the options for a bogie sprung separately from the driving wheels.

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Will L
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Re: CSBs and the Single Bogie

Postby Will L » Fri May 13, 2011 10:56 pm

Solutions With The Driving Wheels And The Bogie Sprung Separately

Having got the options that dealt with a simple CSB solution out of the way, I am back to what I really needed, which was an answer I could apply to the C12 without major surgery. Therefore I was stuck with separate sets of springs over driving wheels and the bogie. The problem I was wrestling with was the fact that, while CSBs work very nicely with that CofG sat centrally over the driving wheels, to get some weight on to the bogie, the CofG was going to have to move. Dealing with situations where the CofG wasn’t central over the CSB have proved highly problematic, and the mathematics impossible to solve.

Or so I thought, until I gave some consideration to the characteristics of a basic 0-4-0 chassis.
CSB C12 draw 3.jpg
CSB C12 draw 3.jpg (79.63 KiB) Viewed 10158 times

A 4 wheel chassis is actually the CSB trivial case. The centre fulcrum goes half way between the wheels and the outer two should be placed symmetrically (i.e. the same distance) either side. They shouldn’t be too close to the axle but otherwise you can put them more or less where you like. I do have a 2 axle version of that spread sheet, but the only useful thing that it will tell you, given the weight of the loco and the position of the fulcrum points is what size of CSB wire you will need. You can probably manage very well without it.

The key point is that the bits of the CSB either side of the centre fulcrum are symmetrical, so with the CofG directly over that central fulcrum, the two sides will have exactly the same spring characteristics. Therefore:-
1. each axle block is displaced by the same amount
2. exactly the same weight is being carried by each wheel
3. the chassis will sit level.

But you can turn that round and say, if the chassis is sitting level, the CSB displacements are the same, and the same amount of weight is being carried by each wheel. Most important of all, the chassis would not sit level if the displacements were not the same.

Therefore if you have a 4-4-0 chassis with one end supported by a symmetrical 4 wheel CSB (an S4CSB!), and the other by a sprung bogie, then, if you had managed to adjust it so the whole chassis sits level, you have exactly the required setup.

Bingo!

Once I’d got there, a couple of solutions suggested themselves.

Option 3 Separate Sprung Bogie, Adjust CofG Location
CSB C12 draw opt 3.jpg
CSB C12 draw opt 3.jpg (46.34 KiB) Viewed 10158 times

Starting with a symmetrical 4 wheel CSB (S4CSB) and separate sprung bogie, chassis balance is achieved by adjusting the position of the loco CofG. When it is not right one end of the loco will ride higher than the other. With the loco body properly mounted on the chassis, measure the running plate or buffer heights at each end and add weight to the high end until it sits level. Once that has been achieved, the driving axles are equally loaded. How much weight is on the bogie will depend on how stiffly the bogie is sprung and how high it sits. For now you will have to guess how springy to make the bogie.

Once you have found the right place for the CofG you can, if you wish, calculate how much of the loco weight is on the bogie. However, as I promised this post would be a maths free zone, details of how to work it out will be in a later one. Many who would be interested will probably have no difficulty working it out anyway. You probably want the bogie springs to be on the soft side, but not too soft or the body may be inclined to pitch forward. If the bogie springs are too stiff you will struggle to get enough weight up front to level the chassis.

If you want to adjust the buffer height, once the chassis is level, you will need to change the CSB wires. If having done that, the chassis won’t sit level, so you will need to add more weight at the high end or take some off the low end.

The sprung bogie can be any design you like, from the single central fulcrum spring beam design shown, to a rigid bogie with a single spiral spring on the bogie pivot pin between the bogie and chassis rubbing plate.

Option 4 Separate Sprung Bogie, Adjusting Height Of The Bogie Pivot
CSB C12 draw opt 4.jpg
CSB C12 draw opt 4.jpg (48.73 KiB) Viewed 10158 times

Again start with a S4CSB and separate sprung bogie. Set the CofG to be 1/3 of the way from the centre of the driving axles to the bogie pin and the bogie will carry 1/3 of the loco weight. You can choose some other weight distribution if you wish. I will post more details on how to work it out, but later. The chassis is made level by adjusting the height of the bogie support on the chassis, effectively adjusting the height of the bogie to suit the amount of defection required in the bogie springing. You have to decide how springy to make the bogie but if you get it wrong you may not be able to get the chassis level. Again the actual bogie can be any design you like and actually it doesn’t need to be sprung at all.

To adjust the buffer height, change the CSB wires and readjust the height of the bogie support. You can imagine a number of possible designs for the adjustable bogie support, I’ve suggested screw adjustment but not how you would lock it in position one you had the level you wanted.

You may not actually need to have an adjustable bogie rubbing plate either because, if the other dimensions are right, you can achieve the same ends by changing the springs in the bogie and/or putting shim washers into the bogie pivot. An adjustable rubbing plate would just be less faff. Once you’ve got your head round the problem, it is obvious that all the factors involved in this design, the S4CSB, the Bogie CSB (actually another S4CSB) and the impact of the CofG location on the weight carried by the bogie, are all calculable using the existing tools. So designs with a fixed bogie rubbing plate will probably become the norm with experience.

Summary

So that’s it, I now feel I can build a 4-4-0 chassis on CSB’s, knowing what factors may need adjustment, and be confident I can get a balanced result that will work and have good haulage powers. With hind sight the two separately sprung bogie options look pretty obvious, that’s probably because they are. It’s realising the implications of having the driving wheel CSB symmetrical that was the logical jump that makes all else clear. These solutions aren’t yet quite as free from post build phase adjustment as an "all wheels under a CSB" job, but they are definitely a cut above having separately adjustable springs on each wheel.

One more thought. Having solved the 4-4-0 problem it is now clear to me how this solution can be extended, certainly to 4-6-0s, and probably to any other loco with a weight bearing bogie.

Next post here will be on how all this was applied to the C12, which employed option 3 by the way. There will also be another post, in time, which goes into the theory and possible calculations in a lot more detail. This will be much more at home in the Abstruse CSB Theory thread so that is where I’ll put it.

Will
Last edited by Will L on Fri Mar 15, 2013 3:58 pm, edited 1 time in total.

Trevor Grout
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Re: CSBs and the Single Bogie

Postby Trevor Grout » Wed May 18, 2011 9:32 pm

I have been asked to post this on Behalf of Bill Bedford.

I am sure that he will see any replys made

"The thing about CSBs is that they are so mind bogglingly simple that people can easily miss how simple they are, and tie themselves in knots thinking up 'solution' to non-existing problems. The basic principle is that the weight taken on a set of axles can be varied by replacing the wire with one of a different size. So WillL's problems with his C12 can be cured simple by using thinner wire on the bogie and pony truck. I suggest that he starts with 14 thou on the drivers and 10 thou everywhere else. Getting a 4-4-2 to balance is a bit of a juggling act but not that difficult. If You want to object that softer springs on the bogie and pony truck will cause proposing, well that seems to be entirely prototypical see http://www.lner.info/forums/viewtopic.p ... nky#p29688"

Regards
Trevor

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Will L
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Re: CSBs and the Single Bogie

Postby Will L » Thu May 19, 2011 12:06 am

Trevor Grout wrote:I have been asked to post this on Behalf of Bill Bedford.

That's useful thank you, as my posts are here, I think its best that issues arising are discussed here.

"The thing about CSBs is that they are so mind bogglingly simple that people can easily miss how simple they are, and tie themselves in knots thinking up 'solution' to non-existing problems.


We agree on the basic point, CSBs are simple, but I have to say problems didn't strike me as particularly non existent when I first found the driving wheels clear of the floor. But, that aside for the moment, as the C12 was a kit, most of the issues I was trying to get to grips with had already been addressed for the C12 by Bills design. What I wanted to know was, if no such aid was available, how should one design and set up such a chassis for one self, and then expect to get it to work well . So most of what I wrote should not be taken as a critique of the C12 kit as such.

As I said in an earlier post
Will L wrote:.. is I'm not trying to have a go at Bill, nor am I terribly concerned about any perceived problems with the kit, some of which may prove to be as much to do with the way I put it together as the kit design. Also if you read back to the top you will be reminded that I didn't start this thread until I was happy I now have a good working version of the chassis. So obviously there is more to come on this.


Trevor Grout on Behalf of Bill Bedford wrote:The basic principle is that the weight taken on a set of axles can be varied by replacing the wire with one of a different size. So WillL's problems with his C12 can be cured simple by using thinner wire on the bogie and pony truck. I suggest that he starts with 14 thou on the drivers and 10 thou everywhere else.
.

To quote one of my own previous posts again
Will L wrote:... The whole thing typifies the basic problem of implementing a sprung chassis with a number of separate springs. It may well be possible to get it to work, but only with a considerable amount of work getting the various springs adjusted correctly. This is of course a problem we share with the prototype, but without benefit of a weigh bridge to tell you just how much weight you have got on each wheel.


I would point out that I already had 14s on the loco and 8s on the bogie, before I chose to do things to the bogie for which Bill cannot be expected to take any responsibility (details in my next post). 8s are the thinnest guitar string generally available, and a bit inclined to bend in use.

I still think there is a design issue with the springs on the pony truck, but as I was happy to settle for no springs at all, I can't say that with certainty.

Trevor Grout on Behalf of Bill Bedford wrote:Getting a 4-4-2 to balance is a bit of a juggling act but not that difficult.


When you read my next post you will see I have achieved exactly that, but more interestingly, I hope, I have developed some ideas as to how to design a 4-4-0 CSB chassis for oneself, and shared them with the readers of this forum.

Trevor Grout on Behalf of Bill Bedford wrote:If You want to object that softer springs on the bogie and pony truck will cause proposing, well that seems to be entirely prototypical see http://www.lner.info/forums/viewtopic.p ... nky#p29688"

No objection from me, in fact I am happy to report the finished C12 shows no visible sign of proposing, or porpoising either. That said, while I think the bogie is sprung softer than the drivers, I don't know that for a fact. One of the outcomes of my thinking is that I do have an easy and practical way of finding out.


On the whole I was quite taken with the C12 chassis kit which is a sound design in almost all respects. It's a pleasure to build and has a number of very neat features. It would be a very rare kit indeed not to find a few points to quibble over. However if you want a fully operational version, you will need to do a bit more than just "shake the box", but I thought that was very much in line with Bills philosophy on these things. I do know that a good working chassis is achievable, cause I've got one.

Will

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Will L
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Re: CSBs and the Single Bogie

Postby Will L » Sun May 22, 2011 9:27 pm

So much for theory, back to practice

Having discovered that the C12 chassis was going to need a little more work, I did my thinking, as explained in the last two big posts, and then I started a little redesign exercise.

I decided that the pony truck could, with advantage, be relegated to being purely cosmetic. Prototypically it should have been a radial axle anyway, but as I didn’t really want to get into ways of springing a radial truck strait off the CSB just at the moment, I let that one pass.

I also decided that I wanted pickups on more than just the four driving wheels, and the bogie was for me the logical choice. Beyond the fact that an effective 0-4-0 does not ride like a 4-4-0, fitting pick ups to the bogie was yet another good reason why I needed a bit of body weight on the bogie, particularly if I didn't want to stop the wheels from going round

The pony truck unsprung

The picture shows the pony truck in place
CSB C12 bits 5.jpg
CSB C12 bits 5.jpg (65.17 KiB) Viewed 9954 times

As the springs for the pony truck were separate from those for other wheels, despringing it was simple, I just left out the spring wires. In this photo the wire you can see is actually the end of the CSB for the driving wheels. The one for the pony truck would have been a few mm above this one. To keep the truck honest I added a significant lead weight, which is what you can see bolted to its frame. A “feature” of the chassis design is that the pony truck pivot is where the brake cylinder ought to be. Thus the pivot is directly below a bit of the fixed break gear detail. This makes it an absolute b***er to get the pony truck frame on to the pivot pin, or to screw in the bolt that keeps it there. But as I wanted to keep the break gear detail, a way had to be found.

Reworking the bogie

While a significant amount of work on the bogie was on the agenda, the one thing I didn’t change was the bogie CSB, even though it didn't allow as much deflection of the axles under load as you might have hoped. Mostly the rework was to do with fitting pickups that neither stopped the wheels from going round, nor restrict the free movement of the bogie by attaching relatively stiff electrical feed wires. I chose a design I have successfully use before, which is based around a pair of sprung plunger pick ups.

Don’t get me wrong, I wouldn’t be seen dead fitting sprung plunger pick ups as intended, which is bearing directly on to the backs of the wheels. They work far too much like brakes, and also restrict the movement of the suspension. However, for the use I had in mind, they are ideal.
CSB C12 draw 6.jpg
CSB C12 draw 6.jpg (67.6 KiB) Viewed 9954 times

Two sprung plungers are mounted vertically in the bogie frame one either side, as in the diagram. The plunger ends bear on an appropriately gapped copper clad pad which forms the bogie rubbing plate on the chassis. The pick ups proper (fine phosphor bronze wire) are soldered to the plunger tail and bear on the back of the wheel flanges. The resultant rim scrappers can be set to have a very light touch. The geometry ensures this remains pretty constant even when the bogie wheels are using up any available side play, and also serves to self centre the wheel sets. The bogie is free to pivot and is not restricted by the feed wires which are attached to the rubbing plate on the chassis.

This set up violates one of my house rules that says that small sub-assemblies of this kind should be removable for painting. As it is otherwise a good system I decided to put up with this small transgression, I just have to ensure that no flux or paint gets into the fine spiral springs behind the plungers.

One last implication of this setup is that, unless you design the bogie pivot specifically so as to prevent it, the plunger pick up springs are now part of the bogie suspension. This bogie now has both primary and secondary springs! This is what convinced me I didn’t need to add any further flexibility in the bogie springs and hence I left the CSB as designed. You will see from the photo’s which follow, the bogie CSB wire is thin, 8 thou steel wire, which makes the pick up wires look positively chunky.
CSB C12 bits 4.jpg
CSB C12 bits 4.jpg (127.59 KiB) Viewed 9954 times

In the photo you can see that the yellow feed wires tuck away neatly and don’t get in anything’s way. Also in the photo you can see the bogie axle blocks, the horn guides that are folded out from the bogie side frame, and the fulcrum tags soldered to the underside of the axle blocks.


Putting it all together


For the sake of interest, this picture shows you all the bits that make up the chassis in a state of near complete disassembly. If trying to decide what goes where, beware that not all the bits are facing the same way round. I could have helped you by having the main chassis and all the bits below it facing the other way.
CSB C12 bits 1.jpg
CSB C12 bits 1.jpg (221.72 KiB) Viewed 9954 times

The bogie pickup rubbing plate and feed wires are what is below the bogie. Also on view here are a number of other bits not discussed else where. There is the main pick up assembly for the driving wheels that bolts to the top of the chassis beneath the motor, the rest of the break gear, and the dummy springing and ash pan detail that bolts on underneath the chassis. The odd shaped scrap of wire below the gearbox is the torque thrust link which connects the gearbox to the up-stand on the main chassis. Finally there is the white plasticard splasher assembly that goes in as the cab floor. It is there to prevent you looking in through the cab door and out through the driving wheels. A point people building enclosed cab tank locos overlook all too often.

Put together the whole thing looked like this. It still needs to have its crank pins cut short, and the proper crankpin nuts fitted. I always use plain old 14ba nuts until final assembly.
CSB C12 bits 2.jpg
CSB C12 bits 2.jpg (149.99 KiB) Viewed 9954 times

If at all possible I like my pickups to bear on the tops of the wheels as they do on the drivers. This means you only need to keep one face of the wheel tyre clean, but you do have to keep in mind that pickups on the top of the wheels are also effectively part of the suspension! These are designed to be soft enough for the CSB to be the predominant spring, but you also need to make sure they bear equally on each wheel so as not to nullify the care with which the CSB fulcrum points were chosen.

Next Time


Having got it all together, the last thing was to get it balanced and running nicely.

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Will L
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Re: CSBs and the Single Bogie

Postby Will L » Mon May 23, 2011 11:15 pm

Getting it to Run.

The Gibson driving wheels have been quartered using the CW jig, as always. The gearbox is a standard Highlevel Loadhauler which, because the design of horn blocks used by the kit maximises the space available, just fits between the frames. Washers eliminated all the side play on the drivers. Only a modicum of opening out of crank pin holes in the rods was necessary and the chassis was soon bind free and turning over sweetly. All in all a nice bit of chassis design.

My only other mod was the up stand I used to attach the torque reaction link, the other end of which went through a hole drilled in the side frame of the gearbox. Bill does provide bits for this but no guidance as to how they fit. I’d gone my own way before understanding dawned.

Balancing the assembled chassis and loco

From the posts further back up the thread, you should have gathered that, as the bogie is separately sprung from the driving wheels, the available options for balancing the chassis resolve around placing the CofG some way forward of the classic “central over the CSB” position. Because the CSB on the driving wheels is a symmetrical 4 wheel arrangement, if the chassis sits level then the weight carried by all the driving wheels will be equal, which is just what we want. So the trick is to get the chassis sitting level. My available choices were either, to set the Loco CofG a fixed amount forward and juggle with the height at which the bogie supports the chassis, or, to adjust the position of the CofG of the loco. In either case you're done when the chassis sits level. Given the bogie modifications involved in fitting the pick ups, only the "adjusting the CofG" position option was really available to me.

For the sake of argument, I did a trial with the body weighted to put the CofG central over the driving wheels. In this state, the results were as you should have expected. The loco was visibly sitting high at the front. The pulling power was very limited, three relatively light bogie coaches had the wheels slipping on the flat, and it was inclined to derail at the slightest excuse.

Measuring buffer heights confirmed that the front of the loco was sitting markedly higher than the back, by more than 1mm at the top edge of the buffer face. So lead was added into the front of the boiler and between the frames over the bogie, until the buffer height was the same front and back. These measurements were not particularly precise, and the possible error could be a few 1/10s of a millimetre, but despite this, the haulage power and road holding were transformed. Now five much heavier coaches could be pulled up an incline with no problem. I’m still waiting to get access to a larger layout to find how big the load has to be before she starts struggling.

And that was it. Off she went to the paint shop, and when last seen she was earning her keep on Knutsford with no issues. All she needs now is lamps and a new layer of coal on the bunker!
CSB C12 veiw 1.jpg
CSB C12 veiw 1.jpg (175.56 KiB) Viewed 9886 times

And Finally

Here ends my planned posts to this thread, although I’m happy to discuss what I’ve done further with anybody who wants to. I hope this has sorted out the options for doing CSB’s on 4-4-0 loco’s and got it to the point where anybody else who wants to have a go can try it and be confidence of success.

One final word, I plan a post or two on the theory, when we might stretch a point and think about 4-6-0s too. I know a lot of you find the theoretical stuff more off putting than helpful, so they will turn up on another thread. After that it will be back to the J10 which requires a lot of non CSB related work.


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