P4/ EM and tight radius curves

[Stubby47]

I've had an idea how tighter curves could be used in off scene tracks for EM / P4 rolling stock, to enable a roundy-roundy layout in a smaller space.

 

(I'm not an EM/ P4 modeller, so all this could be complete hogwash...)

 

As I understand things, the limit to the tightness of a curve is determined by the longest fixed wheel base that needs to go round that curve. This is because the inner rail and outer rail are a fixed distance apart (although this can be eased slightly).

 

Why not remove the inner rail completely and use a substitute such as copper tape ?

 

The outer rail would keep the loco/train in line, whilst the tape would provide the necessary power supply, but the radius could be much reduced, such as 4th or even 3rd radius (using standard Hornby / Peco settrack ).

 

To re-rail the train at the end of the curve would need a chevron and a gradual rising inner rail.

 

Is this a practical proposition, or just plain silly ?

 

Stu

[96701]

I'd guess it would be impractical because the inner buffers would meet, and the coupling would not extend far enough to get the train round the curve.

[bertiedog]

It has been tried before, and the limit is the buffers and couplings limits. I used the idea on a Model Railway shop display in the 70's, it works, but only with soft longer sprung couplings that allowed for the curves, and reverse operation was near impossible, with buffer locking and over riding occurring.

 

For a fixed demonstration display it worked, allowing 00 round 6 inch radius in a hidden loop, allowing an 060 to haul a train consist of wagons.

On a second incarnation I tried magnetic couplings, which worked well, but only as a fixed consist, all prepared to work as a fixed display.

 

I do not think it can be transferred to a working layout with normal operation on it.

 

Stephen

[Bob Reid]

Without the inner rail, what would keep the wheel on the outer rail from dropping off? Short of a check rail all the way round the curve perhaps.

[bertiedog]

Without the inner rail, what would keep the wheel on the outer rail from dropping off? Short of a check rail all the way round the curve perhaps.

The shop window version used a check rail, the flanges ran on the metal plate, on both the rail side and the inner rail less side, would not work without it, pulled stock would be pulled in to centre as the train proceeds. In the display, the check was plywood, routed to fit. The metal was thin brass sheet. The stock was Tri-ang, course scale, all wheels the same form.

Stephen.

[Il Grifone]

There is/was a prototype for this in Italy. The inset track leading to Imperia harbour has (had? - I haven't been there for years) a very sharp curve with one rail replaced with a metal strip at road level (the outer IIRC). Stock travelled over it at slow speed powered by a road tractor.

 

The usual solution for tight curves is gauge widening, which is set automatically by an EMGS track gauge.

[bertiedog]

This was a bit more than ordinary gauge wideening would allow, it was dogbone shape with 6 inch radius curves, and gauge widening was tried but failed, mainly in this case due to the Tri-ang flanges involved, very thick. The friction of two rails with two guard rails was too high, and there is significant trouble with having fixed wheels on axles with no differential.

 

Having the outer running on rail, with a check rail, meant the other side ran only on the tip of the flange on the brass plate, and it slid enough to allow the passage through the very tight curve.

 

On P4/S4 the minimum I got on test was about a foot radius with gauge widening, again friction due to the fixed wheels and no differential becomes a serious issue, and the loco will lose traction on the curves, as one side or the over gains traction and pulls, this causes judder and is the limit of what can be achieved.

 

Stock with loose wheels would work, or locos with one side loose wheels, would work, or proper differential gearboxes!

 

By the way, the gauge widening three point gauges only work to a degree, the design often is a bit of a "suck it and see" design, the widening is only an approximation of the true trigonometric curve needed. The widening only works within certain restrictions, as the curve gets tighter the base of the triangle must increase in true relation to the curve, in other words, a better approach would be a calculated table of increase for each radius, not to rely on the gauge to much.

 

The gauge makes the work easy, as transitions can be followed, but how many modellers do the basic transition curve correctly, even in P4. Transitions are vital as our curves are rarely strict scale, and become critical on tight P4 trackwork, both for appearance and good smooth running.

 

John Allen, in the States, tried a trick method of tight curves, no rails at all, just guide edges, and got 5 inch curves in HO, to "trick" the eye, and force hidden trains around impossible corners on his layout, but it restricted the stock used to only an 060 and short cars.

 

Stephen

[Russ (mines a pint)]

The usual solution for tight curves is gauge widening, which is set automatically by an EMGS track gauge.

as already noted I think there is more limitation due to bufferlock and coupling standards that EM & P4 gauge modeller tends to use

If you wanted to model industrial type railways (which I suspect the OP might?) one way round this would be enlarged buffers (or maybe dumb or no buffers according to prototype?)

[Stubby47]

If you wanted to model industrial type railways (which I suspect the OP might?)

Actually, Russ, it stemmed from a conversation with Penlan and the space needed to convert Penlan into a roundy-roundy, hence the suggestion of 3rd or 4th radius.

Stephen's examples of very tight curves was not really the intention, but I can see where this concept could be used on a small industrial layout..... (no, mustn't ...)

 

Thanks for all the opinions and experiences - the one aspect I didn't consider was the pull of the stock towards the centre of the curve with no inner rail - the potential application would obviously need to accommodate trains of 10-12 wagons, which would cause problems.

 

Stu