Questions on CSB, bogies and other springinging

[thruxton]

Anyone have any thoughts on bogie springing when using CSB on the loco drivers?
I ask because in drawing up a new chassis, I see no particular reason not to treat the bogie (its a 4-6-0) as another driver and also mount it on the CSB (in other words ending up with a calculation for an 0-8-0). In this case, the bogie would have no other springing bar side control.

Also, while looking at CSB for a tender and not particularly wanting false inner frames- and finding things getting very tight- it occurs that tender axleboxes can be easily made as sprung (eg Loveless locos). Any reason this is not more common- I feel an itch to start another 3D printing project.

 

[Steph Dale]

For bogies with CSB I contend you have a point! However, it's worth pointing out that the prototype works by springing the wheels relative to the bogie frame; not by springing the bogie frame to the rest of the chassis. In 7mm at least, the prototypical approach is feasible.
On tender frames you may well be able to spring them in the outside bearings. I've done it on my 2251, using brass wire springs to hold bearings in the outside frames. I have to say that it's not easy and that the frames make up a touch wider than the prototype in the kit. This extra clearance was necessary for the springs.
False inner frames do sort all sorts of issues with tenders, wheelset availability, clearances, etc!
I'll be very interested to see what you come up with.
Steph

 

[ZiderHead]

… Also, while looking at CSB for a tender and not particularly wanting false inner frames- and finding things getting very tight- it occurs that tender axle boxes can be easily made as sprung (eg Loveless locos). Any reason this is not more common …

Ive been wondering about this too and I suspect it partly comes from the tradition of steam loco building where inner frames dominated. With a few exceptions (eg. Westerns, non-NBL Warships and some modern bogie designs) everything else uses outer frames, whether W-irons or bogie frames.

We are used to unsprung wagons and coaches (and even some sprung like MMP) using prototypical outside bearings, but as soon as its a loco the designs default back to inner frames and bearings, even when rigid. Moving the bearings further inboard makes the suspension much more sensitive to spring rates, firmer and visually more "wobbly" - not a good thing at model scales. Not good at full scale either, hence the Western's less than plush ride quality.

 

[Steph Dale]

Jon,
There is another reason, an internal chassis won't suffer stability problems if the springs bottom out. So it's much more tolerant of poor assembly...
Steph

 

[thruxton]

Thanks for the replies. As for the tender axleboxes, I was thinking to adapt the system I'm using on my APT-E (see thread in new members).

Thing is, with regard to a bogie, if it has any form of vertical springing, no matter how light, it wiil have an effect on an otherwise CSB set-up. So my thinking was that its inclusion into one overall arrangement may be a useful way to go. This is bearing in mind 'traditional' springing is really independent to each wheel whereas CSB is interactive along its length of application.

(I do wonder if we simply use stuff now that was first made in days of less readily available technology and perhaps even austerity. Brass is a fine example of this where people will sing its virtues, damn any mention of modern plastics and happily ignore crumbling metal on models of yore.)

 

[Steph Dale]

The available CSB models can actually be 'tailored' fairly easily to allow for multiple springing arrangements.
Certainly allowing for a 4-6-0 with a CSB across driven axles with an open-sprung bogie isn't either theoretically or practically difficult. It's just fxxx ugly if you can see between the frames.
Steph

 

[thruxton]

Steph- what I had in mind was to incorporate the normally fixed bogie mount into the CSB set-up so the entire front assembly would be dealt with as a 'driver'. I don't see any difficulty in the actual design as basically the concept would just act as another set of hornblocks.

 

[Steph Dale]

Yep that'd work. To keep the CSBs free moving you might be better to use two sets (two 0-4-0 arrangements) rather than one large one (an 0-8-0). In either case just watch out for clearances around the front fulcrum; you may find that it's difficult to find somewhere to hide it.
Just a thought.
Steph

 

[Bill Bedford]

After trying a whole lot of variations of sprung bogies, I've found that the easiest way to implement them is to follow the majority of prototypes and use a compensation beam that is sprung to the bogie frame. This gives enough movement in the axleboxes to deal with any pitch freedom and, with a wide bearing plate or side support cups, is stiff enough to counteract any tendency for the loco to roll.

As usual, modelling the real thing turns out to be a whole lot easier than trying to invent model 'solutions'.

 

[thruxton]

Steph, the project in hand presents frames substantial enough to hide a lot of sins and providing relative oodles of space. I hope to start a work in progress thread in a month or so. I think I might even be able to compare 0-8-0 with 2 X 0-4-0 in the same frame (custom axleboxes pinching an idea or two from High Level Models and Hobby Holidays).

 

[thruxton]

Bill, your method is actually my 'fail safe' but at this stage I have the freedom to draw up a variety of 'suspension' set-ups at relatively low cost- and I have to admit to enjoying this sort of fiddling.