P4: 3' Radius with Gauge Widening OK?

[Lacathedrale]

In another thread I'm bouncing around some ideas for a garage layout - one of the options is to revisit P4 (as opposed to 00, or embarking on a new adventure in 3mmFS), but my main problem is that with only around 8' overall width available to me, the 180° curve to enter a fiddle yard needs to be a no more than a hair under 3'3" radius.

 

I'm specifically looking to model the late victorian period - so the largest locomotives would be six coupled tender engines with a 16'3" wheelbase, the longest stock is likely to be 40' bogie coaches.

 

An example of the kind of constraint I'm talking about is shown below, though the track plan is fairly notional the curve is just about what I'm "stuck" with in any scenario...

 

The three parallel tracks show potential traverser/FY positions.

 

P4 isn't the only option of course - I can attempt to reevaluate EM, consolidate down to 00 for the sake of expediency, or change scales - but for now, I'm curious as to whether with gauge widening I can consider this combination of track curvature and stock to be "safe".

 

 

[martin_wynne]

@Lacathedrale

 

Hi William,

 

A better option is an egg-curve, transitioning down to a short length of tighter curve at the centre of the turn:

 

 

Here the minimum radius on the inner track is 797mm (31.4") which is tight for P4 but perfectly acceptable if sufficiently gauge-widened. The important point is that there is a very short length of it, so less likely to cause problems with couplings and buffer locking.

 

The great advantages of doing this are that running will be much improved as stock is eased gently into the curve; you have a longer length available for the station throat; and appearance is much improved as the severity of the curve is disguised (especially if you have the middle section hidden, such as behind a backscene, in a tunnel, or behind a large building).

 

You can see that I have adjusted the track spacing for running clearance -- 6ft way on the straight at the bottom, 8ft way at the centre of the curve, 6ft-6in way at the top for the easier curve.

 

You can choose how much "egginess" to go for, but it will always improve the running to transition into sharp curves.

 

cheers,

 

Martin.

[Siberian Snooper]

Tim Venton's exhibition layout Clutton has 3ft radius return curves and that's inP4, so no reason not too.

 

http://www.gwr.org.uk/layoutsclutton.html

 

[Lacathedrale]

@martin_wynne is there a way to achieve that transition curve/eggy curve in Templot without the use of multiple templates? It's something I've done from time to time but always using multiple templates with differing curve radii and I'd like to replicate what you've done in my space - it looks wonderful!

 

@Siberian Snooper thank you kindly for your link there, good to know I'm not barking completely up the wrong tree.

[Brinkly]

35 minutes ago, Siberian Snooper said:

Tim Venton's exhibition layout Clutton has 3ft radius return curves and that's inP4, so no reason not too.

 

http://www.gwr.org.uk/layoutsclutton.html

 

 

Clutton is a really good example of what can be achieved with tight curves in P4. One thing to say though is that all the locomotives have a fair amount of sideplay on the middle axles to enable this. 

 

 Please excuse the grainy footage (taken a very long time ago on my phone) but it shows an ex GWR mogul (etched chassis I believe) running on said 3ft curve. 

 

 

Some more footage here showing the 3ft curves. 

 

I do like Clutton and seeing it in back in BRM circa 2007 made me go back into modelling again. 

 

Best wishes,

 

Nick.

 

[Lacathedrale]

That is fantastic to see, thank you - glad to see it's feasible.

Edited April 24, 2022 by Lacathedrale

[martin_wynne]

1 hour ago, Lacathedrale said:

@martin_wynne is there a way to achieve that transition curve/eggy curve in Templot without the use of multiple templates? It's something I've done from time to time but always using multiple templates with differing curve radii and I'd like to replicate what you've done in my space - it looks wonderful!

 

@Lacathedrale

 

Hi William,

 

I'm not too sure what you mean by multiple templates? You can't build a track plan without using several templates.

 

Here I have offset the centre of the egg to make more space for the station throat. You can see that it's possible to start the first crossover only 18" from the end of the layout (yellow mark):

 

 

 

Here are the templates in different colours. It would be difficult to get fewer than this, but I don't understand the need to?

 

 

 

cheers,

 

Martin.

[Lacathedrale]

Sorry, I meant multiple templates for the transition/egg curved track specifically! i.e. what was the method you used to create that curve? Did you start with the smallest radius and then make a transition curve from a straight section attached to the throat?

Edited April 25, 2022 by Lacathedrale

[martin_wynne]

3 hours ago, Lacathedrale said:

Sorry, I meant multiple templates for the transition/egg curved track specifically! i.e. what was the method you used to create that curve? Did you start with the smallest radius and then make a transition curve from a straight section attached to the throat?

@Lacathedrale

 

Hi William,

 

Yes. Start with the outer two larger curves, and then position a smaller one between them. Adjust its radius and position so that the space from the first two templates is something of this order:

 

 

Use F6 to adjust its radius, use F7 to position it, or use these buttons:

 

If there is too much space, the transition zones will be too long and overlap -- no good. If there is too little space,the transition zones will be very short with a long length of the sharper middle curve. Some trial and error will be needed to get just what you want. It helps to practice a bit before diving into the final design -- as with everything in Templot. 🙂

 

 

 

 

 

More about transition curves in Templot:

 

 https://85a.uk/templot/companion/transition_curves.php

 

More about creating a transition curve between existing templates:

 

https://85a.uk/templot/companion/make_transition_link.php

 

cheers,

 

Martin.

Edited April 25, 2022 by martin_wynne

[Lacathedrale]

That's perfect, thank you! So just to be 100% clear, with a gauge widening of +0.25mm on a 800mm radius in the apex of the egg, I should be OK for 4-4-0, 2-4-0 and 0-6-0 locomotives? Obviously I need to test it - but if the principle is sound then I can forge ahead elsewhere with that ideal.

Edited April 25, 2022 by Lacathedrale

[Siberian Snooper]

If it was me, I'd knock up a trial length including the tightest part of the curve and part of the transition and try my locos on it before committing to the actual build. A few copper clad sleepers, 2 lengths of rail  and 10 or 15 minutes with a soldering iron would save one helluva lot of frustration if my locos didn't want to play.

 

 

[martin_wynne]

1 hour ago, Lacathedrale said:

That's perfect, thank you! So just to be 100% clear, with a gauge widening of +0.25mm on a 800mm radius in the apex of the egg, I should be OK for 4-4-0, 2-4-0 and 0-6-0 locomotives? Obviously I need to test it - but if the principle is sound then I can forge ahead elsewhere with that ideal.

@Lacathedrale

 

Hi William,

 

You can get any vehicle round any radius, even a dinner plate, by widening the gauge sufficiently. The difficulty comes with the couplings and buffer locking, especially if mixing very long vehicles with very short ones. You might need a bit more than +0.25mm on 800mm, but provided you don't go so far that a wheelset can fall between the rails, it will be fine (for plain track). For P4 wagon wheels that's about 19.75mm gauge, or say 0.9mm widening maximum.

 

If you add a continuous check rail on the inside of such a curve, make sure you widen the flangeway gap by the same amount.

 

cheers,

 

Martin.

Edited April 25, 2022 by martin_wynne
typo

[Lacathedrale]

Would a check rail actually function? Interesting!

[Siberian Snooper]

9 minutes ago, Lacathedrale said:

Would a check rail actually function? Interesting!

 

Should do! I can't see any reason why they wouldn't, they do the job on turnouts.

 

 

[Izzy]

I do wonder if with tighter radius a checkrail might cause rubbing of the leading and trailing edges of the rear of flanges (relative to the wheel diameter), and thus restrict the amount of sideplay and limit how tight a radius any particular vehicle could cope with. A standard 3-point track gauge, ( 90 degree angle at the single leg), will of course give automatic gauge widening with the amount relative to the tightness of the curve, the tighter the more produced.

[proton]

On 24/04/2022 at 03:14, Lacathedrale said:

In another thread I'm bouncing around some ideas for a garage layout - one of the options is to revisit P4 (as opposed to 00, or embarking on a new adventure in 3mmFS), but my main problem is that with only around 8' overall width available to me, the 180° curve to enter a fiddle yard needs to be a no more than a hair under 3'3" radius.

 

I'm specifically looking to model the late victorian period - so the largest locomotives would be six coupled tender engines with a 16'3" wheelbase, the longest stock is likely to be 40' bogie coaches.

 

An example of the kind of constraint I'm talking about is shown below, though the track plan is fairly notional the curve is just about what I'm "stuck" with in any scenario...

 

The three parallel tracks show potential traverser/FY positions.

 

P4 isn't the only option of course - I can attempt to reevaluate EM, consolidate down to 00 for the sake of expediency, or change scales - but for now, I'm curious as to whether with gauge widening I can consider this combination of track curvature and stock to be "safe".

 

 

Hi,

 

I model P4 and my minimum curves are 3' radius, definitely with gauge widening.  A J39 goes around with no problem, as does a Jinty, and a class 45.

 

John

[AndyID]

Thinking out loud I'm wondering if dissimilar metals for the rails on the tight radius bits helps. Perhaps steel one side and nickel silver on the other? This might encourage differential action. On the other hand it might not help at all 🙂

[Enterprisingwestern]

On 25/04/2022 at 14:33, Siberian Snooper said:

If it was me, I'd knock up a trial length including the tightest part of the curve and part of the transition and try my locos on it before committing to the actual build. A few copper clad sleepers, 2 lengths of rail  and 10 or 15 minutes with a soldering iron would save one helluva lot of frustration if my locos didn't want to play.

 

 

 

Have you seen how much copperclad is these days, far too valuable to waste on trial lengths!!

 

Mike.

[Siberian Snooper]

4 hours ago, Enterprisingwestern said:

 

Have you seen how much copperclad is these days, far too valuable to waste on trial lengths!!

 

Mike.

 

 

I would still do it, because it would save wasting a lot more, on building a layout that was inoperable, due to the locos not being able to negotiate the curve. They could either be incorporated into the layout or recycled, for further use in a fiddle yard.

 

 

 

[martin_wynne]

5 hours ago, Enterprisingwestern said:

 

Have you seen how much copperclad is these days, far too valuable to waste on trial lengths!!

 

 

It doesn't have to be copper-clad, because it doesn't need to be electrified.

 

Use scrap bits of rail, etching scrap, etc., as sleepers, at a wide spacing.

 

Martin.

[Lacathedrale]

The solution seems to be to test as suggest, but also in general size to provision the terminus of the layout to be no longer than 9' - which would leave me enough space for a 4'6" traverser board in a straight 'FY to Terminus Exhibition Layout' arrangement. Either way then, I'm quids in!