J94 CSB chassis questions.

Simon Moore
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J94 CSB chassis questions.

Postby Simon Moore » Wed Jan 06, 2021 9:56 pm

I am currently getting parts together to build my first csb chassis & i have a few questions.

I have been looking on the forum & the clag website & its like wading into a minefield of information with a lot of it going over my head.

I have found a fulcrum point diagram for a j94 chassis & ì have the high level jig, hornblocks & spring carriers at the ready.

What i am struggling with is what size markit handrail knobs i need, i have some short ones & long ones in stock?

Do i need to place them at a certain height or does the three holes on the high leveĺ carrier just cater for the best placement on the chassis?

What gauge wire do i need & what material does it need to be made from?

Finally what weight do i need to be aiming for on the finished model?

I am currently making a rumney models 16t wagon chassis & i am very impressed with the results so far hence wanting to spring the j94.

Any input would be greatly appreciated.

Simon

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Paul Willis
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Re: J94 CSB chassis questions.

Postby Paul Willis » Wed Jan 06, 2021 10:38 pm

Simon Moore wrote:I am currently getting parts together to build my first csb chassis & i have a few questions.


There will be a Will Litchfield along in a day or two with all the answers...

What Will can't explain about CSBs isn't worth knowing. I could have a stab at a couple of those questions, but there are far better people out there than me to explain.

A couple of things I will say though:

- it's not as difficult as all the maths makes it seem (and indeed you don't really need the maths at all)

- there is more flexibility in the technique than may first appear to be the case. Like so much of P4, there is a certain element of "what works for you" (and your particular model).

Cheers
Paul
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bevis
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Re: J94 CSB chassis questions.

Postby bevis » Wed Jan 06, 2021 11:27 pm

Good evening Simon,
With regard to the High Level Jig then, yes, the holes are to offer options for best fit. There's a useful tutorial on the High Level Site at: http://www.highlevelkits.co.uk/jigpage.html
Have fun!
Bevis

Winander
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Re: J94 CSB chassis questions.

Postby Winander » Wed Jan 06, 2021 11:38 pm

Hello Sim,

This is the index to Will's Buckjumper build in case you haven't found it already, you should find all you need to know https://www.scalefour.org/forum/viewtopic.php?f=96&t=6934#p75311.

IIRC the bottom of the three holes causes interference, so best avoided if possible.

Best wishes and please remember to keep us updated.
Richard Hodgson

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Will L
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Re: J94 CSB chassis questions.

Postby Will L » Thu Jan 07, 2021 4:32 pm

Sorry my response took longer than I (or Paul) expected, I hit an snag.
Simon Moore wrote:I am currently getting parts together to build my first csb chassis & i have a few questions.

I have been looking on the forum & the clag website & its like wading into a minefield of information with a lot of it going over my head.

I have found a fulcrum point diagram for a j94 chassis & ì have the high level jig, hornblocks & spring carriers at the ready.

I'm assuming you found the plot on the CLAG website. In answering one of your questions I feed the plot on the CLAG website into my CSB spread sheet and it did not give a satisfactory result. So I tried again with Alan Turners spreadsheet which works in an entirely different way and that didn't agree with the weight distributions claimed for it either. I've sent a message to whoever is maintaining the CLAG website at the moment. In the mean time, please can I suggest you go with the following plot. The diagram gives all the relevant dimensions.
J94 CSB plot.jpg
J94 CSB plot.jpg (64.59 KiB) Viewed 1066 times

You needn't worry about the Chassis gradient and Center Axle bias boxes just note that they are green. They go red if the plot isn't good enough. Nor need you worry about Y1,2 and 3. The measurements are all in mm The p and q boxes give the wheelbase (5'9" - 5'3") The Fs are the fulcrum locations, the Ws the axle locations, a, b, c, d are the plot dimentions.
What I am struggling with is what size markit handrail knobs i need, i have some short ones & long ones in stock?

I've gone over this a couple of times on the forum. In the thread Winander suggested there is a post that cover this question and several others that are likely to come up as you fit the Hornblocks and fulcrum points, see Part 7 - At last assembly begins
The specific point about handrail knobs is near the end. The answer is that the short ones are fine, but there is rather more to it than that.
Do i need to place them at a certain height or does the three holes on the high leveĺ carrier just cater for the best placement on the chassis?
The Highlevel jig places itself on the axle centre line. The CSB wire normally runs above this line but exactly how far above will depend on the individual chassis. The axle block fulcrum etch give you three options, and you choose the one that best suits your chassis. So yes it just caters for the best placement on the chassis. If you use the ones closest to the axle centre line, the CSB wire will not pass the top of the Hornguides which needs to be filed down slightly, just enough to allow the wire to go past.

What gauge wire do i need & what material does it need to be made from?

Finally what weight do i need to be aiming for on the finished model?

These answers are connected. Just how heavy your model needs to be depends on what you want it to pull. If it will only ever be required to do really light duties, then an adhesive weights down to 25 grams an axe (the usual advice for other vehicles) will probably do. The usual advice for locos (with Trump style levels of evidence to back it up) is 50 grams an axle. If you want to pull heavy trains up hill a total weight over all the driving axles of 250 grams or greater is probably what your aiming for. Also note that it is important to get the loco's centre of gravity over the centre of the driving wheel base, and its theoretical exact postion is also given on the plot. While sub millimetre precision in this is not necessary, In the right place it will ensure the the springs share it equally across all the driving wheels for maximum pulling power. Get it very wrong and the loco wont sit level and it may make it inclined to go strait on at corners.

Once you have finished the loco and weighted it as necessary, you can feed the actul weight back into the CSB spread sheet to find out what size wire will get you closest to the desired .5mm spring deflection. It was at that stage I discoverer I wasn't happy with the plot on the CLAG website.

For the spring wire, we use steel guitar strings which come out of packet strait enough. They are cheep and available in the range of sizes we want. Googly "Ernie Ball Strings" to find online suppliers or visit your local music shop once lockdown is over. They start at 8 thou and go up 1 thou at a time to 20. 8 is about right for 25gm axle weight and so is good for wagons too. I've never needed anything bigger than 14. There are other more expensive brands available which go up in .5 thou steps for the really picky. However I also use a 20 thou wire when building a chassis as, without the body weight, this is near enough rigid and so allows me to check I've made the the whole thing square when stood on a flat surface (the traditional sheet of plate glass.)

For the plot I gave above the following table gives weight against spring size

Loco weight in grams - 75 -110 -170 - 250 - 350
Wire size in thou --------8 ----9 ---10 ---11 ---12
Choose the wire size closest to your actual body weigh

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zebedeesknees
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Re: J94 CSB chassis questions.

Postby zebedeesknees » Thu Jan 07, 2021 4:47 pm

Simon Moore wrote:I am currently getting parts together to build my first csb chassis & i have a few questions.
I have been looking on the forum & the clag website & its like wading into a minefield of information with a lot of it going over my head.

Have you found this page yet? http://www.clag.org.uk/beam-annex4.html
The target deflection is around 0.5mm, and for a six-coupled, the spans between the fixed fulcrum points of the outer axles need to be a couple of mm shorter than that over the centre axle to get relatively even loading over all the axles. The detail of the dimensions given on the CLAG site, to tenths of mms, is there to provide the absolute optimum in drawbar pull; one mm either way in any of them is very unlikely to produce a noticeable difference.
I have found a fulcrum point diagram for a j94 chassis & ì have the high level jig, hornblocks & spring carriers at the ready.
What i am struggling with is what size markit handrail knobs i need, i have some short ones & long ones in stock?

What matters is the distance between the base of the flange and the centre of the handrail hole. This should match the distance between the inner face of the frames and the hole(s) in the High Level carriers when the bearings are in place, so that the CSB wire is straight in the transverse plane. The knobs I use are Markits M4HRK 1.5 Original, where this dimension is 1mm.
Do i need to place them at a certain height or does the three holes on the high leveĺ carrier just cater for the best placement on the chassis?

Provided the deflection requirement is met as in the link above, any can be used. Chris included those options so that gaps in the frames or interference from such as brake hangers could be avoided.
What gauge wire do i need & what material does it need to be made from?

This is the 'How long is a piece of spring?' question! (sorry...) The original inspiration for the springs of CSBs came from looking at an electric guitar and realising that the plain - not wound - strings were spring steel wire in diameters of 1 thou increments. They are relatively cheap and available on line, and most have a thin Nickel coating to help resist corrosion. I keep 7 gauge to 19 gauge, mostly the Ernie Ball make, but for a loco somewhere between 11 and 15 should be right.
Finally what weight do i need to be aiming for on the finished model?

Generally, get as much weight as possible in the model, keeping the centre of mass as near to the longitudinal centre as possible. Then choose the spring wire gauge to give the deflection that puts the buffer height in the right place. The wire should not be fixed anywhere, but be free to slide in all of the fulcrum points. It is then easy to change to a different diameter to get the ride height where you want it once the weight is settled.
I am currently making a rumney models 16t wagon chassis & i am very impressed with the results so far hence wanting to spring the j94.
Any input would be greatly appreciated.
Simon

These are the crude technician's answers, I hope they help!
Ted.

Winander
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Re: J94 CSB chassis questions.

Postby Winander » Thu Jan 07, 2021 5:20 pm

All very helpful but to be clear, is the target deflection 0.5mm in either direction, i.e. 0.5mm up and 0.5mm down?

In addition to not fixing the wire, ensure it is free to slide when deflected - for instance if you need to make slots in chassis spacers, and it has wiggle room at each end, but not so much that it can slide out of a fulcrum.

Dave Franks, Lanarkshire Models does more substantial knobs for the fulcrums, CSB00 CSB Anchors, heavy duty knobs - pack of 10 £3.00 http://www.lanarkshiremodels.com/lanarkshiremodelsandsupplieswebsite_199.htm. He uses High Level components so they should be suitable as I expect (or hope, as I've bought some) they are designed for those components..

Good luck and let us know how you go on.
Richard Hodgson

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Will L
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Re: J94 CSB chassis questions.

Postby Will L » Thu Jan 07, 2021 6:17 pm

Winander wrote:... is the target deflection 0.5mm in either direction, i.e. 0.5mm up and 0.5mm down?


The CSB when not bearing any weight at all is in the 0.5mm down position. It should be strait at that point. When stationary standing on its wheels, the wire should be deflect up by 0.5mm. From that point the wire should be free to deflect 0.5mm either way.

The thing that makes CSB system different is that it ensures deflection is possible in both directs and the vehicle is thus truly ridging on its springs. Most other springing systems to date have tended to have the axle pressed against either the top or bottom stop and thus can only move one way..

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zebedeesknees
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Re: J94 CSB chassis questions.

Postby zebedeesknees » Thu Jan 07, 2021 6:42 pm

Winander wrote:All very helpful but to be clear, is the target deflection 0.5mm in either direction, i.e. 0.5mm up and 0.5mm down?

Down restraint is of little consequence, in fact the Bill Bedford J72 chassis has(had) hooks in the frames rather than knobs, and bearings that are circular with the sides machined flat to fit in the guides. The radius tops of the bearings just rest under the wires. This idea works perfectly well. The only consequence is that the bearings have to be retained by a keeper, or the wheels and the wires can fall out when the loco is lifted from the track.

In addition to not fixing the wire, ensure it is free to slide when deflected - for instance if you need to make slots in chassis spacers, and it has wiggle room at each end, but not so much that it can slide out of a fulcrum.

Yep, and methods of controlling the sliding of the wire are suggested in the beam-annex4 link I posted earlier.
Ted.

Winander
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Re: J94 CSB chassis questions.

Postby Winander » Thu Jan 07, 2021 7:57 pm

Thanks to you both. That has clarified a few things for me, and hopefully helped Simon.
Richard Hodgson

davebradwell
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Re: J94 CSB chassis questions.

Postby davebradwell » Fri Jan 08, 2021 10:40 am

Just weighed my Austerity - it's 292gms. This should be easily achievable and I think there's just a couple of layers of lead around the tank. Motor is horizontal so can't be much in the boiler. There's decoder and speaker in there, too.

I would suggest you have less weight on the centre axle to make the short wheelbase more stable - with axles close together there can be a tendency for these things to have a poor idea of horizontal which can tend to vary. Mine isn't csb but the springs can rise and fall - it can't count as sprung, otherwise. There's plenty of springing systems which work properly, eg coil, cantilever but they can all be made to sit on the stops if the spring is too weak, even a csb.

DaveB

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Will L
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Re: J94 CSB chassis questions.

Postby Will L » Fri Jan 08, 2021 4:07 pm

davebradwell wrote:...I would suggest you have less weight on the centre axle to make the short wheelbase more stable - with axles close together there can be a tendency for these things to have a poor idea of horizontal which can tend to vary.

Traditionally we have advised making the centre axle a little soft, based on the idea that the chassis might oscillate about the centre axle, and that making it a bit softer than the outer two would help to counteract this tendency. While this is a theoretical possibility, my experience had suggested it was not a real problem. My current builds, small wheelbase 0-6-0s show no sign. I now think that it doesn't happen with traditional CSB chassis, particularly given a good even weight distribution. This is probably because the frictional forces in the sliding axle blocks, and spring movement through the fulcrums, is sufficient to damp out any tendency to oscillate.

As to the chassis sitting level, an asymmetric wheel base make it hard to get weight distribution exactly even and chassis precisely level. My suggest post for the J94 is very close to an even weight distribution and the expected Chassis Gradient (a measure of how far from level it would be) is 1 mm in 2931 which is as near to level as makes no odds. Both my J56 and J69 are asymmetric to. They sit level and show no sign of doing anything else.

Just like the real thing, any sprung chassis will tend to lift at the front when picking up a load, and dip when slowing a train down, as one of the Knutsford East Crew were keen to point out. Weather he ever really observed it on the CSB fitted locos is another matter.

Taking our thinking about weight on the centre axle a bit further, on the CSB for a Single Driver thread we have been discussing using the possibility of fitting CSBs to LBSC 2-2-2 single drivers. Exactly how the prototype tackled the weight distribution came up, as, presumably this was as much a problem for them as it will be for us. They certainly ran with significantly more weight on the centre driving axle than the carrying axles either side.

davebradwell
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Re: J94 CSB chassis questions.

Postby davebradwell » Fri Jan 08, 2021 8:24 pm

Well, I wasn't happy with my loco when I had it set up for equal weight distribution so decided to adjust it. I agree it's not an issue on longer wheelbase engines but that slight friction in the horns combined with the short wheelbase means it's worth being careful. It'll depend how stiff the springs are, of course but if you're going to fix the weight distribution at the design stage it seems wise to take precautions against any possible problems. I've never had an engine oscillate unless it has a wobbly wheel. These WDs are much bigger and heavier than your Buckjumpers or other vintage GE engines and were rated 4F by BR.

DaveB

Simon Moore
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Re: J94 CSB chassis questions.

Postby Simon Moore » Sat Jan 09, 2021 1:27 pm

Sorry for a late reply to my post!

Unfortunately i have been working nights trunking trailers from West Yorkshire to Wolverhampton & back. I did briefly read the replies but i couldn't digest it properly.

I think everyones input has been great in answering my questions. Will you answered yet another that cropped up whilst dicing with snow on the M6!

This was how to check you had built the chassis square. I'm going to order some additional bits today now i have a shopping list of parts to complete the chassis.

The weight distribution was something else that i was concerned about & i was hoping to use the cast metal weight from the original model in the saddle to evenly distribute weight.

Thank you to everyone who has replied to this post its all been very helpful & answered plenty of questions i have had.

I hope to make a start this next week, i will post in my workbench thread once i start. I will link it to this post.

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Paul Willis
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Re: J94 CSB chassis questions.

Postby Paul Willis » Sat Jan 09, 2021 9:50 pm

Simon Moore wrote:I think everyones input has been great in answering my questions. Will you answered yet another that cropped up whilst dicing with snow on the M6!

This was how to check you had built the chassis square. I'm going to order some additional bits today now i have a shopping list of parts to complete the chassis.


Hi Simon,

I'll just change the emphasis of your question slightly. As for kit-built/scratchbuilt chassis, you will almost certainly be springing them or compensating them. In that case, it is less important that the chassis is square, but that the axles and the coupling rods are square.

Indeed, I've built an Alan Gibson J15 kit where due to my own cackhandedness, the chassis frames were actually shaped like a banana. However, because the axles were parallel, and matched the coupling rod centres, it ran very sweetly. I ultimately rebuilt the chassis, but that was for different reasons.

First of all, make sure that your coupling rods are straight, true and of the same length. It's said that physics means that a locomotive will work with (slightly) different coupling rod lengths, but I really wouldn't want to go there.

Then, the key stage is to set up the hornblocks to the same centres as the coupling rods. The posh way to do this is to use something like an Avonside chassis jig:

IMG_7797.JPG


The less posh (but still perfectly adequate) way of doing it is to use what are called jig axles. I don't have a photo of my set in use, but this is one in place, followed by the full set. The idea is that you use them to hold the hornblocks in the correct place whilst you solder the axle guides into the frames. The coupling rods are slipped over the extended ends, to ensure that the hornblock centres (and thus the axle centres) match the centres of the holes in the coupling rods.

Pug build 025.jpg
Pug build 025.jpg (59.89 KiB) Viewed 687 times


Axle jigs 001 (Medium).jpg
Axle jigs 001 (Medium).jpg (43.47 KiB) Viewed 687 times


In that way, you should have a square assembly that the chassis then sits around, as it were.

Simon Moore wrote:I hope to make a start this next week, i will post in my workbench thread once i start. I will link it to this post.


I'll very much look forward to it. All the best, and don't forget to shout if you have any questions.

Cheers
Paul
Beware of Trains - occasional modelling in progress!
www.5522models.co.uk

Simon Moore
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Re: J94 CSB chassis questions.

Postby Simon Moore » Sun Jan 10, 2021 12:35 am

Evening Paul

I have both those tools i have only just started using the old style hornblock jigs as the avonside is what i have built many rigid chassis on it.

Thanks for the help i am sure i will have many more questions to ask.

Thanks

Simon

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Paul Willis
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Re: J94 CSB chassis questions.

Postby Paul Willis » Sun Jan 10, 2021 9:50 am

Simon Moore wrote:I have both those tools i have only just started using the old style hornblock jigs as the avonside is what i have built many rigid chassis on it.


Ah, excellent. In which case, you'll be familiar with how it works.

In terms of getting the chassis square (your original question) the main thing to consider is using the various "fences" to hold the chassis square as you construct it around the hornblock guides. In essence, it's just the same as a rigid chassis but the frames are "floating". The fences help hold them square as you solder the spacers, etc. together.

Cheers
Paul
Beware of Trains - occasional modelling in progress!
www.5522models.co.uk

davebradwell
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Re: J94 CSB chassis questions.

Postby davebradwell » Sun Jan 10, 2021 10:16 am

A vital step is to number each axlebox and mating hornguide and mark the tops so that every time you re-assemble the chassis it goes back the same way. Also deburr everything - every axlebox hole should be reamed and have a large drill twizzled in the ends to put a tiny chamfer on the edge and straight edges stroked with a fine file. Burrs (Small dents or surface damage) will push the parts to one side when using the jig and throw them off-centre. Take a long time over this - it'll also make for a smoother running chassis. Check and clean-up the axles.

Biggest source of trouble is excess clearance between axlebox and hornguide.

DaveB

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Will L
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Re: J94 CSB chassis questions.

Postby Will L » Sun Jan 10, 2021 11:57 am

davebradwell wrote:Well, I wasn't happy with my loco when I had it set up for equal weight distribution so decided to adjust it. I agree it's not an issue on longer wheelbase engines but that slight friction in the horns combined with the short wheelbase means it's worth being careful. It'll depend how stiff the springs are, of course but if you're going to fix the weight distribution at the design stage it seems wise to take precautions against any possible problems. I've never had an engine oscillate unless it has a wobbly wheel. These WDs are much bigger and heavier than your Buckjumpers or other vintage GE engines and were rated 4F by BR.

I suspect the dominant fictional damping on a CSB chassis is from the CSB wire moving in the fulcrum points, as they are supporting the full loco weight. I know of one CSB non believer who things this should be enough to stop them working at all, which fortunately we know to be untrue. Russ always wanted us to lubricate them but I've never bothered. It is a significant difference between CSBs and individual axle springing as achieved by your modules. My view would be that with difficult prototypes like the J94 with its short wheelbase and high CofG, a CSB chassis would have a distinct advantage in this respect and be much less liable to have level stability issues. My J56 while not directly comparable, it weighs in at 230 gm is a few mm longer and lower, but it is still a short heavy model and it shows absolutely no signs of this problem.

Paul Willis wrote:..I'll just change the emphasis of your question slightly. As for kit-built/scratchbuilt chassis, you will almost certainly be springing them or compensating them. In that case, it is less important that the chassis is square, but that the axles and the coupling rods are square...


Ho, hum. While there is truth in this, the reason why I adopted the CSB thick wire while building approach is as the result of managing to build a chassis with one end fulcrum point displaced upwards. This caused all sorts of problems till I spotted it. So I still think getting the basis squareness of the chassis right is remains a useful aim. I will agree it is less critical than with a fully rigid chassis.

I too have a (OO compensated) chassis with a surprising and clearly visible fault (axles not parallel) which persisted in running reliably and well, however I think getting away with it isn't an argument for not doing my best to avoid it in future.


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