Sub 4ft radius curves

[the fatadder]

With my first child being expected in January, my layouts current location has become unavailable. As a result I have spent the last couple of weekends insulating and putting up plasterboard to convert the garage into a new home for the layout. As a result I now have a fair bit more space to play with…

My plan was to design a continuous run fiddleyard which could be used with both my Kites Croft and Blackcombe layouts. However, the overall width of the converted garage is only 7ft11 inches which prevents the use of 4ft radius curves that I understand are the generally accepted minimum.

Now for bogie diesel stock I don’t really see an issue with this, however I am much more concerned about how my stem stock will perform. In particular, 8 coupled 2800 and 4200 class along with various GW 4-6-0s.
The majority of which will have sprung (I think I have 3 rigid chassised Hornby locos which will remain so unless Brassmasters were to release a replacement) Rolling stock is all based on sprung chassis, with smiths couplings and (for the moment at least) solid buffers.


Having done some quick calculations and I think that the maximum radius I can manage is going to be 3ft6, and ideally I would also like to have a second track inside this (though I realise that is going to be really pushing the running quality for large locos, the main reason for the second track is going to be the diesel layout.)

I know of layouts which have gone for tighter radius curves (iirc Clutton is around the 3ft mark)
So I would be interested to hear experiences of larger steam locos on sub 4ft radius curves, and what I need to keep in mind both for track and chassis construction to ensure reliable running on these curves.

Thanks for the help
Rich

[martin goodall]

The main line curve on "The Burford Branch" is 3-foot radius (and the carriage siding, being an after-thought, has a radius of no more than abvout 2' 10").

What determines whether locos will go round the curves is not the overall size of the loco but the amount of sideplay allowed for the middle axle. However, a big 4-6-0 might look a bit silly going around a curve of that radius, even though it may be possible to achieve it by suitable adjustment of the frames and hornblocks/hornguides.

I can tell you from experience that you can get a six-coupled P4 loco (such as a Dean Goods or a Pannier) round a 2-foot curve if it has sufficient sideplay on the middle axle. We tried it once on my old "Crichel Down" layout. A Pannier and a Dean Goods which both had plenty of sideplay in the middle axle coped with the 2-foot curves on that layout without difficulty, but another Pannier which had little or no sideplay in the middle axle fell off.

My own experience has taught me that locomotives (and other rolling stock) should be built specifically for the layout on which they are intended to run and adjusted accordingly.

[Philip Hall]

I have converted a few 4-6-0s and 2-8-0s to P4 and all have been quite happy at 2'6"radius although I wouldn't expect to hurtle around at that speed. 3'0" to 3'6" is quite practicable, and indeed was going to be my own ruling radius until the possibility of a larger space came up. As Martin says, build for the layout the engines are going to run on. With a 4-6-0, I tend to allow sideplay on the middle axle, hardly any on the front behind the slidebars, and a little bit on the rear axle.

2-8-0s, such as the Hornby 28XX and the Bachmann ROD 2-8-0, need a slightly different approach: here the front and third axles have very little sideplay (slidebars again), with some play on the second axle (care behind the connecting rods) and quite a bit on the rear axle. The tender coupling should prevent the rear of the engine swinging around too much. An interesting point about these two particular engines is that the front and third axles have a little bit of upward play, so that the engine actually rests on only two axles, the second and third. I am talking about only a few thou here, and have only recently been able to check this with some test wheels and a surface plate which I obtained in order to check the truth of another kind of Bachmann engine. It may well be that Hornby and Bachmann have deliberately done this to assist with transit around sharp curves, but whatever, it helps us in P4 as well. I have found no need to introduce any kind of downward springing, the weight of the wheelsets seems to be enough to keep things on the rails.

This upward play is also apparent on some six coupled engines, and does not affect running adversely on these either.

Philip

[Andy W]

Congratulations Rich. I hope all goes well with the birth. You may have more space for playing trains - but will you have any time?

[the fatadder]

Thanks for the advice, I will take that into consideration when i get on with my conversions.

I think I will look at building the layout with a double track curve in this case with the outer track being 3ft 6 and the inner slightly less

Will find time somehow post arrival, at any rate she can nap in the train room with me (hopefully)....

[Paul Townsend]

Will find time somehow post arrival, at any rate she can nap in the train room with me (hopefully)....

So speak many a proto-parent
I got four of the tee-shirts so gently suggest you may be a tad over-optimistic
The first few weeks may well go by the book and then it all falls apart!

Never mind, take the long view.......

[Ian Everett]

The Bradford North Western Branch has a 3'6"curve and my Bachman WD and Hornby Black 5 romp round it. The G5 0-4-4T is a little less happy!

I'm sure you will succeed if you follow the advice above.

Ian

[DougN]

Oh don't say that Ian, I have one that is almost complete, a G5 that is, I was hoping to get it to match my other locos that I set to go around a 1metre radius. I want to have a look at that over the Christmas holidays but I think I may run out to of time as it is only 3 weeks and the list is rather long.


Merry Christmas to all!

[Simon_S]

Congratulations Rich but don't expect much modelling time when the little one arrives! Sub 4' radius no problem in Brio railways though

[Ian Everett]

Oh don't say that Ian, I have one that is almost complete, a G5 that is...

I built the G5 mainly for Humber Dock, the main line of which is virtually straight and the 3'6" curve on BNW is temporary. The G5 does get round it but with a lot of flange grinding. I'm sure that with a bit more side play than I have given her she would be fine. (At present she runs so well elsewhere that I'm loth to take her apart. Chance plays a large part in my modelling success or otherwise...)

Ian

[steamraiser]

Tim Venton's (Of this parish) Clutton layout runs with 180 degree 3ft radius ends in P4.
The locos do need a touch more sideplay, but generally run fine.

Gordon A
Bristol

[DougN]

Thanks Ian, I have one part built and waiting for me to complete the chassis. I thought that due to the bogie having such limited swing it was causing the problems. I will have to look further into the entire mech.

All the best

[steves17]

Its a relief to find this thread. I decided to abandon Peco 100 at the eleventh hour. Talking at the P4 stand at the NEC was the tipping point otherwise i would be on 'toy track ' now. One thing i didn't bank on was the increased curvature. Four foot is huge - 8 ft plus for U-turns. I've been able to get up to 3ft radius or so as a minimum with massive re-planning and some heavily altered boards but if sub 3ft can be done with some tweaking them i'm at a little more ease.

[Knuckles]

Its a relief to find this thread. I decided to abandon Peco 100 at the eleventh hour. Talking at the P4 stand at the NEC was the tipping point otherwise i would be on 'toy track ' now. One thing i didn't bank on was the increased curvature. Four foot is huge - 8 ft plus for U-turns. I've been able to get up to 3ft radius or so as a minimum with massive re-planning and some heavily altered boards but if sub 3ft can be done with some tweaking them i'm at a little more ease.

But you fell and went back to 00!!


Just read the whole thread and am thinking is it worth redesigning my layout slightly? I don't really care if engines will look silly going around a tighter than desirable curve as long as they go around it.

I designed my layout with 4' curves on the outside and the immediate inner ones a wee less and the branch again a little less.

I'd like to get those 4' curves don to 3'6" or even 3" if at all possible as the track is basically almost hugging the roof eves and I could do with an extra 6" -1' for scenery and back scene but as I plan to run a couple of Pacifics and 10-Wheelers I do worry if things will manage.

What do you guys think? Resurrecting old threads can be good.

[Philip Hall]

My only reservation about fairly tight curves is not that engines cannot be built to run around them, merely that big engines will look a bit daft when they do. This is much less obvious if you are viewing from the inside, which is what I was planning to do a few years ago when I was restricted to a space 15'6" x 10'6". My new building will be at least 21'6" x 19'6" inside so 4'6" radius minimum suddenly became possible. I still intend to go below that on parts of the hidden yards and at the ends of sidings, but the main running lines will be able to be generously curved.

I would say that if you get a more workable and visually pleasing railway by reducing the radius a little, and you're viewing it from inside, go for it.

Philip

[Knuckles]

It is viewable from inside only pretty much. I could do with bringing the curves in a bit from the edge so the backscene scenery can be built up a bit more as the track is almost going into the crook of the roof eves.

17.5ft x 11ft is the max space I got.

Bottom of the page is the plan...

viewtopic.php?f=9&t=2133&start=75

Unless I redo it in Templot first so I can put some transition curves in and redesign the turnout geometry to fit. But currently I still haven't got past the 2nd tutorial.of building a single slip, exasperated because Bullguard keeps jamming it up and quarranting files.




I'm more bothered about running than visuals as it is a compromise I actually need due to the usual.issue of having less space than really needed for a given plan.

I just fear building 3' or 3'6" curves then finding out getting a pacific or black 5 around it is next to impossible.

[John Donnelly]

I just fear building 3' or 3'6" curves then finding out getting a pacific or black 5 around it is next to impossible.

Dave Bradwell's 9F chassis will go round a 3' radius curve so you should be in with a good chance with a Pacific...

John

[Philip Hall]

I would go for 3'6" as a minimum then, with maybe 3'0" in yards and sidings where big engines will not go.

Philip

[SHurst]

Dave Bradwell's 9F chassis will go round a 3' radius curve so you should be in with a good chance with a Pacific...

I think you will find that in his instructions for the 9F Chassis, Dave states:

"My own model will run around 1 metre radius, laid accurately with a template"
"The limit on radius is probably set by the brake hangers which trap the wheel flanges between inner and outer parts and so restrict the allowable side play. This will be more of a problem in EM and OO with thicker flanges than with P4"

Not so sure about a 3 ft radius therefore- but may be wrong - will ask Dave next time we operate Derwenthough !

Simon

[Knuckles]

This is all pretty promising. To get a 9F around a 3' curve seems phenomenal.
You can always bodge the brake hangars and file them back a little so the flanges are not in the way, I find this is sometimes a good idea.

Thing is, in P4 the frame width as I understand it is supposed to be 16mm's so that leaves less than 1mm of play either side. Is that considered generous? Seems restrictive to me.

Maybe instead of publishing the minimum radius as 4' it should be stated that 4' is the minimum radius where things still look ok and then a smaller minimum for running but worse visuals? I've seen that suggested before but can't remember where.

I may try to redesign the layout with 3'6" then, (Maybe 3'??) and see how it looks.

[John Donnelly]

Dave Bradwell's 9F chassis will go round a 3' radius curve so you should be in with a good chance with a Pacific...

I think you will find that in his instructions for the 9F Chassis, Dave states:

"My own model will run around 1 metre radius, laid accurately with a template"
"The limit on radius is probably set by the brake hangers which trap the wheel flanges between inner and outer parts and so restrict the allowable side play. This will be more of a problem in EM and OO with thicker flanges than with P4"

Not so sure about a 3 ft radius therefore- but may be wrong - will ask Dave next time we operate Derwenthough !

Simon

Thanks for that, I was taking the 3' from one of his MRJ articles and a brief chat at S4N last year. Derwenthaugh - now that's a layout I'd like to have a go on especially as the real place is just 10 minutes from my house...

John

[Enigma]

Try and build in transitions so that the radius gradually reduces and then increases which should help to guide the locos through the smallest radius section. Done carefully, the overall 'average' radius can still be 3' or whatever else you can manage to fit into your available space.

(Don't tell anyone but I've done this with Peco Setrack on my US HO layout using gradually decreasing then increasing 'number' curves in the 180' curves at each end. It certainly helps the Mallets get round! But don't worry - I'm P4'ing again now )