Bogie Springing

[Susie]

Hi All.

Could I have some suggestions please regarding springing of coach bogies?

Is the general concensus in favour of two-way springing, so the axlebox moves up as well as down, or for the axlebox to sit at the top of the slot and only move down to accomodate a low spot in the track - if ever there was such a thing in S7?

From an engineering point of view, the latter is obviously the easier, both for the making and setting up, but can those with running experience give their views?

Thanks in advance,

Susie

 

[Dog Star]

Hi Susie,

I prefer to incorporate active suspension with up and down movement of the wheels ... rather than the form of suspension where the permtted movement is only to accommodate a drop in the rail.

My preference is based upon the impression given by stock moving along plain track and over crossings.

regards, Graham

 

[JimG]

Susie,

I would go for what you term two-way springing. I always feel that there is more benefit from springing when it absorbs the bumps rather than following the hollows. With separate wire springing - i.e. not CSB so far - I have been pleasantly surprised at how easy it is to get a vehicle to sit in mid position on its springs. I have used Russ Elliot's wire spring formulae on the CLAG web site and found the calculated data to be pretty accurate. If you have got a good idea of the weight of the vehicle, then you can calculate the proper spring for each wheel. And there is also a good range of guitar wire in one thou increments from 0.007" to 0.020" to give you a bit of elbow room if the vehicle turns out to be different to the planned weight.

One thing I haven't had experience of is secondary springing which can be used in bogies but I believe that is to deal primarily with isolating the vehicle body from bogie movement.

Jim.

 

[Steph Dale]

Ditto; there is a geometric/load problem with outside-framed axleboxes if they don't have freedom to move up as well as down.
Steph

 

[Susie]

Okay, Thanks guys. Two-way springing it is.

(By the way Jim - not a word about this S7 to you-know-who!)

 

[Scale7JB]

Hi susie, did you get the bogies from John?

JB.

 

[Bill Bedford]

With short wheelbase vehicles like bogies secondary springing is more important than primary, and controlling roll is more important than controlling pitch.

 

[Susie]

Hi susie, did you get the bogies from John?

JB.

Hi Johnathan, Yes thanks - it was looking at them and the Kirk mouldings that got 'bogies' rattling round my brain! Hence the questions about springing.

With short wheelbase vehicles like bogies secondary springing is more important than primary, and controlling roll is more important than controlling pitch.

Hi Bill, could you expand on this please? The bogies that I'm doing are for an Ian Kirk Quint-art set for Love Lane, but as I'm interested in coaches anyway (GNR in particular) I'd be interested in your input.

Are you saying that in, say, the Gresley double bolster HD bogies, the coil springs between the upper and lower halves of the bolsters (which due to the hanging links presumably also have some controlling effect on the sideways movement of the bolsters between the inner cross members) is more important than the leaf springs above each axlebox? If correct, I can see how that would be so in full size, as the track also moves up and down as the wheels go over it, so they tend to stay on the rails, but what happens on a model where the track is all but ridgid?

Sorry about that rather rambling paragraph, but if you know what I'm talking about it should make sence, and if you don't, it won't matter!

Susie

 

[Pugsley]

Are you saying that in, say, the Gresley double bolster HD bogies, the coil springs between the upper and lower halves of the bolsters (which due to the hanging links presumably also have some controlling effect on the sideways movement of the bolsters between the inner cross members) is more important than the leaf springs above each axlebox? If correct, I can see how that would be so in full size, as the track also moves up and down as the wheels go over it, so they tend to stay on the rails, but what happens on a model where the track is all but rigid?

I think what Bill is saying echoes my observations of the way that prototype (HST) bogies react. The bogie will tend to pitch into the dips with the secondary suspension doing the work, the primary suspension hardly moving. There is no reason why the model should behave any differently, whilst there is some track deflection in the prototype, in scale terms it may as well be rigid.

To that end, when I get round to building my 108 DMU, I'm going to keep the Easybuild rigid bogies, but will build in secondary suspension, which will help keep it on the rails, and should let it float along in a similar manner to the real thing.

 

[Bill Bedford]

To simplify, in traditional swing link bogies, the primary springs take out any vibrations induced at the wheel/rail interface, the secondary springs control the pitch and roll of the body relative to the bogie frame and the swing links move the centre of roll of the body to somewhere above the roof.

 

[Susie]

Well, I've had bogies rattling round my brain for a couple of weeks now, and thought I had better start making some items.

First up are the Spencer damping units, which are positioned at either end of the primary springs (getting to know the jargon, you notice). These are very noticable on the prototype. I needed 48 so thought I had better make 50+.




I'm going to have a go at flanging the solebars up from 0.3mm copper sheet which is about scale thickness. The trial bit in nickel went okay, so I need to make the flanging plates now, and get stuck in. I am going to have a trial at a simplified version of the secondary springing , but need a bogie to try it out on first!

Susie

 

[JimG]

Susie,

How did you make your 50+ damping units - form tool? If so, how did you make the form tool?

Jim.

 

[Susie]

Hi Jim,

You are quite correct; I did use a form tool.

There are actually two tools used. The first is a 1" diameter disc of silver steel which has the profile required turned on it. This is then used to make the form tool proper, which will be a negative of the item, again on a 1" disc of silver steel. Both are hardened right out, and not tempered.

Here is the drawing I used, scaled from the GA I have of the bogie:




The upper, feint, numbers show "thou in" (ie the cut required) from the outer diameter of the tool blank, the next ones being the diameter required. The lower set of numbers are distances from the base of the unit (the -.125 is for a mounting spigot). The lowest numbers are the distances from the right hand end of the item. This is so the when turned, I can zero the lathe tool on the outer diameter and the end of the blank, and then just work to the numbers. Note that the whole thing is just over 9mm long.

Here are the two tools, the form tool proper still on the holder:


The left hand cutter shows the profile of the spring units. The profile of the form tool is this:



The protrusion on the right hand end acts as a parting tool, to cut off the previously made spring unit.

The cutters have a 6mm hole through them. To turn the discs, they are bolted through this hole on to a bit of brass bar held in the chuck, which has an M6 tapped hole. The segment cut out of the disc is what makes it into a cutting tool. The amount varies according to the diameter of the cutter, but cutting away to about (0.06" x largest diameter) below the center line is about right. The segment can be cut out using either a hacksaw or preferably milled.

The form tools were hardened by heating to red heat using a propane blow torch, and then quenched in water.

The hole is then used to mount them on the holder, which is just a bit of 1/2" square mild steel with a 6mm hole in it. The upper surface had to be milled away to raise the form tool enough so that the cutting edge was at centre height.

For simple profiles it can be quite possible just to turn the negative required straight onto the form tool blank, without going through the double cutter process.

Susie

 

[Dog Star]

Susie,

Please excuse this old bear asking a question... given that there are at least three suppliers of LNER double bolster bogies in 7mm (JLTRT, Sidelines, Peter Dobson) then why are you offering such a tantalising topic on making your own version?

In choosing the material for the sideframes, why are you going for copper rather than brass or nickel? I ask because the all-up-weight of a JLTRT Gresley is close to 1Kg and that might induce deformation of the bogie solebars (yes I understand that you are building Kirk kits... something as nice as a sprung 8'6" bogie to run under JLTRT carriages will go rather well under our teak set ).

 

[Susie]

Hi Graham,

An answer that an "old bear" might sympathise with:

When I started, the only ones I knew about were the Kirk, Kemilway and Cavalier bogies. The Kirk ones seemed too basic, the Kemilway ones were too complex, and the Cavalier ones, sold by ABS, are no longer in production!

I really wanted to have properly flanged solebars rather than mouldings, and the trial I did (using nickel) certainly produced a very rigid item. The replies I have had on this thread regarding the springing also have had some bearing on my wanting my own design.

In fact the coach bodies were originally going to be scratch built too, using the Jenkinson method. I had almost finished the sides, when I realised I had made a basic error in marking them out, so gave up and bought the Kirk kit.

The other thing is that I don't really like making models, but do enjoy working out how to make them. This partly explains my woefully low output of models. The main structural components of the bogie have been thought through and tested; the main lump being a silver soldered framework of profile milled brass. Copper was chosen for the solebars as its ductility makes it easier to flange over a former: the nickel needed three annealings.

Best wishes,

Susie (a lover of teak!)

 

[JimG]

Hi Jim,

You are quite correct; I did use a form tool.

Susie,

Thanks for that. I keep forgetting about making silver steel form tools. Somewhere, I've got a bit of 1" silver steel bar which I got many years ago to try making form tools but never got round to using it. I'll have to search through the steel drawer and do a spark test until I find it.

I've got one or two things that need repetitious machining where a form tool would be the best way of doing it, so I think I'd better start doing something about it.

Jim.

 

[adrian]

You are quite correct; I did use a form tool.

Thanks for the guide, another useful technique to add to the toolbox. However I note that the the locking nuts are nicely formed hexagonal, were these machined as well or just a judicious use of pliers? All very impressive.

 

[Susie]

Aahh! You know the pliers trick too! I got it from Wingrove's book on car modelling.

 

[D G Williams]

Can I ask Susie and Jim - how do you turn silver steel? When I tried it the finish was far from smooth. An internet search for information on the subject was not very helpful!
David.

 

[JimG]

David,

Susie is probably the best to answer since I haven't done it for a while ( ). But I would use a tool with a good bit of top rake. I would use high speed steel or carbon steel - I still have a set of Myford carbon steel tools which I use regularly. Carbide insert tools would probably work well too but for form tool cutting you usually have to use specially shaped tools to form the shape which usually means grinding the tools, and that is not all that easy with carbide. I would also use a fair bit of cutting oil - I apply the oil neat with a paint brush while cutting.

Jim.