Building a G.W.R. Castle + more in 7mm OF from a JLTRT kit restarts on P.88 by OzzyO,

[daifly]

Hello Miss Prism,

 

thanks for all the above. Getting the true weights for the 517s is a bit of a guess, but it looks to be some thing like this. Leading coupled, 10tons 12 cwt. + driving coupled 11 tons 16 cwt. + trailing 8 tons 18 cwt. The wheelbase that I'll be using will be 7'4" + 7'8" total 15'.

OzzyO.

If you are interested in prototype info, a GWR 517 weight diagram published on p116 of 'The Watlington Branch' by J. S. Holden shows:

leading coupled 11t 17c full and 9t 13c empty

trailing coupled 13t 2c full and 11t 9c empty

trailing wheels 11t 3c full and 8t 0c empty.

The CG is 1 5/8" (1.625") aft of the trailing coupled axle centreline

 

HTH

 

Dave

[Miss Prism]

Or should you have two small collars one each side of one of the pivot points?

 

It's a pertinent question, Ozzyo. For a CSB with multi-fulcrum frame points (an 0-6-0 say), the beam tends not to drift along the chassis too much, and the ends of the beam can usually be trapped longitudinally by the body buffer beams. With a springy equaliser with one frame fulcrum point, as you will be using over your drivers, the tendency to drift will be more marked, and some way has to be found of trapping the beam longitudinally, and I can't think of anything better at the moment than your suggested two collars (bits of cable sleeving?) either side of your main frame fulcrum. In 4mm, beams tend to be very thin, and it's usually not a great problem, with some planning ahead of suitable apertures in frame spacers/motion plates, to wiggle in the beam through (typically the back of) the chassis and the handrail knobs etc, but in your case, the large beam diameter, both for your drivers and the trailing wheel, probably precludes this. Leaving aside for a moment the questions of whether the beams and blocks are going to be 'droppable', I think the first step is to determine how the beams can be inserted into (and removed from) the chassis. The trailing axle beam can probably be trapped at its front end by a plate, with the rear end trapped by the body. The big equaliser over the drivers is the tricky one.

[Miss Prism]

Hmmm, seems a bit over-engineered, but:

 

[Jon Fitness]

[ozzyo]

Hello all,

 

thanks for sticking with me asking all these questions about CSBs and a big thank you to Miss Prism for all the help. If some of you had thought that OzzyO had lost the plot with all the questions I'm posting some scans of the N/S etch to try and show why I'm asking them.

 

Frames top left.

 

Spacers and more bits to fit between the frames on the right.

 

A close up of the frames and overlays to try and show what I'm going to be working with.

 

Lets start with some of the problems that I can see now.

1], the axle C/L to the top of the frame is only approx. 8mm.

2], the motion bracket is going to be very close to where the pivot point has got to be. I'd also like to keep the slide bars in there as well, if I can.

3]. the rear face of the cylinders is very close to the front axle. This could work for me, as it could be used as a point to stop the CSBs from moving forwards. But I've still got to fit some horn guides in as well.

4]. pick-ups now this does look a big problem. With all the bits in between the frames and very shallow frames to start with, this loco may have to be built with full split axles and frames (you'll like that Sandy). The driven axle is about the hardest one to do as the gear box can bridge the gaps. If I go this way I'll be able to have pick-up on all six wheels.

5]. the rear axle is going to be under a long frame spacer so I may have to do the short CSB on this one.

6]. looking at the full split frames for pick up the hardest part is going to be the brakes. But I may be able to make some muffs and screw them in at the top of the frames, but only if the screws will be hidden.

7]. how do I insulate the frames from the body?

 

Lets look at some of the positive side.

1]. a well designed kit by M. M. that you can work on.

2]. I'm looking forward to building it.

3]. it's going to be my first build in S7.

 

So looking at the two above lists, three wins over seven in this case.

 

OzzyO.

 

[Horsetan]

The Beattie Well Tank is much the same, Ozzy. Other engines with a weak frame top line in kit form include the SECR "C" and "O1". Also the ex-LBSC E4, I think.

[Ian G]

I am trying to understand all this as I have a 7mm Beattie to build.

 

Ian G

[steve fay]

Get that 517 back in the box and finish the hall!!!!!!!!!!!!!!!!

Then open the 517 again.

[N15class]

I am trying to understand all this as I have a 7mm Beattie to build.

 

Ian G

I have a Shedmaster one that visits the bence sometimes it has compensation at the moment but I am tempted by this CSB thingy too.

Maybe some kind words to miss prism may help.

[Grasshopper John]

I'm with Jon Fitness here, i think i got lost on about page 2 tbh all this techie stuff and no one has even said what a CSB is,

Central Services Bureau ?

 

It's ok my coat is on the stand, getting it now.

 

Grasshopper John.

[billbedford]

I despair, really do. I just don't don't understand why people have so much difficulties understanding something as simple as springing locos with single wires.

 

Especially after watching this 

[Sandy Harper]

Thank you for your link Bill, I found it fascinating.

Sandy

[Miss Prism]

I can see the attraction of split frames, but in this particular case the prospect of splitting the cylinder and motion plates doesn't seem to warrant dismissing the slight difficulty of getting a reasonably inconspicuous pickup on the front driver (the rear driver and trailing axle are not a great problem, the tops of those wheels being readily accessible).

 

Getting the beams to avoid frame spacers and the motion plates etc doesn't need to be a problem provided the apertures are planned. See here. (The front turndown of the rear 517 frame spacer could be dispensed with without sacrificing frame strength.)

 

Provided the equalising beams are close to the frame, they will not interfere with the slidebars. It looks as though you will have to trim one side of the hornguide adjacent to the rear cylinder plate to an absolute minimum.

 

The frame height above the driving axles is uncomfortably small, and the equalising beam fulcrum will be close to the top of the frame, so the beam ends will need to be close to the top of the hornblocks.

[Pete Harvey]

The main thing that is worrying me about the whole thing of (CBS) what ever it stands for, is that everyone is quoting 4mm modelling and refers to info gathered from 4mm projects and other than the basic principal being possible in theory things are different on 7mm models mainly due to the weights and centre of gravity of the constructed models and the inertia that can be generated by a working model the moments calculations need to be done dependent on the final weight and type of the loco being built or it could tare it's self to bits on the first running session.

 

Coil Spring compensation may be old but it is reliable and a proven technology on 7mm models and should not be discounted as a mix of the two technology's may prove to be a better solution when modeling.

[ozzyo]

I despair, really do. I just don't don't understand why people have so much difficulties understanding something as simple as springing locos with single wires.

 

Especially after watching this 

 

Hello Bill,

 

I can't get it to open.

 

I don't have any problems with how springing using a single wire can work in springing a set of loco frames. In fact I think it should be about the best way of doing it. All I'm after is some info. on the best way of doing it. Why reinvent the wheel.

 

Miss. Prism,

 

I'm not that worried about making the split frames as I've been looking in to this more than I have about the CSBs, As my starting point it will be make up the frame spacers as they are then solder some copper clad under  them I'm not sure about single or double sided just yet ( I think that I'll go for double sided as that will mean that I can solder from the top and bottom). One of the good things about building this kit in S7 is that I can test prove some of my ideas on the narrow frame spacers before I commit to any thing on the actual build.

 

The motion bracket I'll probable make from some 1mm copper clad. as I think that the 0.8mm N/S is a bit on the thin side. I may take it up to 1.5mm and then mill it to look more like the real thing? If it can be seen.

 

The holes through the spacers should not cause any problems (I hope). The hight of the pivots above the axle box's may. I'm also thinking about making some curved tops to the frames above the front wheels.

 

For the fixing of the brake gear I'm thinking about making some top hats out of Paxalon and tapping them approx 12BA to fit the brake hangers to.

 

For the split axles, the front and rear ones no problems as it's just a small turning job for them. The gearbox axle is a bit more of a job, as I'd like to keep the gearbox insulated from all of the frames etc. so this will mean a three part axle two parts for the pick-ups and one part for the gear box to fit onto.

 

But all of the above is after I have finished the next two locos. So it's a month or two off just yet. but I do like to plan ahead for this type of work.

 

OzzyO.

[billbedford]

The main thing that is worrying me about the whole thing of (CBS) what ever it stands for,

 

I think you have just proved my point about modellers being unwilling to learn

 

Coil Spring compensation may be old but it is reliable and a proven technology on 7mm models and should not be discounted as a mix of the two technology's may prove to be a better solution when modeling.

 

I'm happy that you think coil springs work for you, but that is no reason for you to trot out your spurious arguments  to try on put others off.

[Pete Harvey]

Bill

 

I'm not trying to put any one off using this type of suspension but from a technical perspective nothing that has been said makes much sense and it is as if not all of the possible outcomes from fitting this type of suspension to a 7mm Locomotive model have been covered.

 

I'm sure that it would work fine on a unpowered 7mm carriage, wagon or tender but everything changes on a powered heavy Locomotive

 

If it works out to be ok with heavy 7mm locomotive kits then great, it's one thing to try this out on a £20 replacement chassis but something else on a £400 JLTRT Castle or King.

 

Just because it woks on 4mm doesn't mean it will work the same way on 7mm

[billbedford]

I don't have any problems with how springing using a single wire can work in springing a set of loco frames. In fact I think it should be about the best way of doing it. All I'm after is some info. on the best way of doing it. Why reinvent the wheel.

 

Continuous Springy Beams were developed to not only improve the efficiency of loco suspensions, but also to make locos in general easier to construct.

 

I've looked at the etched frames you intend using and offer these suggestions:-

 

The frames are pierced for plunger pickups -- so use them.

 

Use the motion bracket as the centre anchor point.

 

The outer anchors placed symmetrically outside the axle centres. Ideally for a four coupled loco they should be placed 1/3 of the coupled wheelbase from the axle centres, but in in fact any symmetrical placement will work. And your case the pickups will be in the way.

 

This will mean that you will have to drill holes in the rear face of the cylinder block to accommodate the spring wires. However -

 

The frames have been designed with "modeller's licence" to have a flat top. Once the loco is built the eye of any observer will be so irresistibly drawn to the fact that the back of the wheel is visible where there should be solid frame as to make the suspension arrangements all but invisible.

[ozzyo]

Continuous Springy Beams were developed to not only improve the efficiency of loco suspensions, but also to make locos in general easier to construct.

 

I've looked at the etched frames you intend using and offer these suggestions:-

 

The frames are pierced for plunger pickups -- so use them.

The frames are not designed for CSBs so does that mean I should not use them?

Use the motion bracket as the centre anchor point.

 

The outer anchors placed symmetrically outside the axle centres. Ideally for a four coupled loco they should be placed 1/3 of the coupled wheelbase from the axle centres, but in in fact any symmetrical placement will work. And your case the pickups will be in the way.

If the pick-ups are going to be in the way, how can I then use CSBs?

This will mean that you will have to drill holes in the rear face of the cylinder block to accommodate the spring wires. However -

 

The frames have been designed with "modeller's licence" to have a flat top. Once the loco is built the eye of any observer will be so irresistibly drawn to the fact that the back of the wheel is visible where there should be solid frame as to make the suspension arrangements all but invisible.

IIRC, I did mention that I was thinking about putting a curved section behind the wheels on top of the frames.

 

OzzyO.

[billbedford]

The frames are not designed for CSBs so does that mean I should not use them?

 

It means that using plungers will be an awful lot easier than trying to use split frames.

 

If the pick-ups are going to be in the way, how can I then use CSBs?

 

It's the symmetry that is important. Having equal distances between the front anchor and the front axle and the rear axle and the rear anchor is more important than the exact value of that distance. So you can choose any anchor-axle distance if you use the same value at both ends. The only caveat is that the closer the anchors are to the axles the lighter the spring wires have to be.

[billbedford]

I'm not trying to put any one off using this type of suspension but from a technical perspective nothing that has been said makes much sense and it is as if not all of the possible outcomes from fitting this type of suspension to a 7mm Locomotive model have been covered.

 

I'm sure that it would work fine on a unpowered 7mm carriage, wagon or tender but everything changes on a powered heavy Locomotive

 

If it works out to be ok with heavy 7mm locomotive kits then great, it's one thing to try this out on a £20 replacement chassis but something else on a £400 JLTRT Castle or King.

 

Just because it woks on 4mm doesn't mean it will work the same way on 7mm

There have been two spreadsheets written to help people quantify the loads and the anchor positions. One was based on Static Beam Theory and the other on Finite Element Analysis. Both gave comparable results. I find it inconceivable that increasing the linear scale of a model by a factor of less that two would break such real world engineering tools. Or perhaps you believe that 7mm to the foot scale has some magic properties which don't obey the normal rules of physics?

[Adrian]

Coil Spring compensation may be old but it is reliable and a proven technology on 7mm models and should not be discounted as a mix of the two technology's may prove to be a better solution when modeling.

 

Coil springs provide suspension but I don't understand how it can be called "compensation", traditional coil springs on individual axle boxes just gives independent suspension, as far as I'm aware there is no compensation provided.

 

Bill

 

I'm not trying to put any one off using this type of suspension but from a technical perspective nothing that has been said makes much sense and it is as if not all of the possible outcomes from fitting this type of suspension to a 7mm Locomotive model have been covered.

 

I'm sure that it would work fine on a unpowered 7mm carriage, wagon or tender but everything changes on a powered heavy Locomotive

 

If it works out to be ok with heavy 7mm locomotive kits then great, it's one thing to try this out on a £20 replacement chassis but something else on a £400 JLTRT Castle or King.

 

Just because it woks on 4mm doesn't mean it will work the same way on 7mm

 

A Castle was probably the wrong example to choose to argue your point - have you studied the 12":1ft. version? With the exception of working leaf springs then CSB is probably the closest you can get to the prototype suspension, between the drivers on the full size loco the leaf springs are attached to a compensation beam and not the frames. So from a technical point of view if it's good enough for the full size loco I think I should be ok in 7mm.

 

In the past I've built quite a few loco's with coil spring suspension and yes they do work ok but not without a being a little fiddly to set up but it doesn't provide any compensation. Compensation is a well proven system but in my view doesn't work that well in 7mm due to the direct link between axle box and loco. With the extra mass and volume then you need some form of springing between the axle box and the loco. CSB in my view is a very elegant and simple solution, it provides compensation between the axles and yet allows the loco to be fully sprung as well, so it's the best of both worlds. I've built a 7mm Jinty and have a running chassis for a Scale7 MOK 4MT (slightly more than the £400 JLTRT locos) both using CSBs - I'm more than happy with the ride quality and I'll be using for any subsequent loco builds.

[Pete Harvey]

Bill

 

I have had a lot of experience with FEA systems in real world situations designing safety critical solutions for the automotive industry with real world consequences if the systems fail, so what you are saying would be right if we could scale down all of the material properties too then the normal rules of physics would apply.

 

Adrian

 

Weather the model is of a Castle or a Duchess is inconsequential the fact that it is a very heavy, very long multiple axle model and if you compare it to your Jinty which is light, short and naturally balanced and the forces acting on the jinty would not have much affect but on a bigger multiple axle model there would be a lot of forces acting on bearings, rods and the chassis that must be considered if not the damage may not happen straight away but after six months of running considerable damage may of occurred.

 

 

If you want to spread the weight of a model over five or six axles and achieve the maximum traction from the driving wheels and to have suspension as well, fitting Compensated Single Beam suspension may work for a light multiple axle model on its own or for a heavy multiple axle model both types would work better, you could also go the whole hog and use working multi leaf spring suspension on every axle and use a beams as a Dampers.

[buffalo]

Pete,

I only work in 4mm so I'm confused as to what these mysterious destructive forces that you are postulating are? Perhaps a worked example would help to show how in two otherwise identical sets of frames, hornblocks, wheels, axles, etc., differing only in their modes of springing one might provide long and reliable service whilst the other will tear itself to pieces.

 

Methinks a little research into what Continuous Springy Beams are and how they work might not be amiss.

 

Nick

[steve fay]

Is that Hall finished yet?