Curved crossover on an incline?

[84f]

I need to add a crossover into my new layout plan. It will be on a 44 inch curve which means a D12 to ensure a minimum 36 inch radius. That would be ok, but it is also on an incline of 1 in 70, and over the start of the transition towards level. There is no super elevation as it close to the the station throat, but I am concerned that I may have problems building it and getting trains to run across smoothly and pick up reliably. Am I right to be worried? 

Thanks

Robin 

[Andy Reichert]

Any curve on an incline will slightly twist the track that diverges away from the incline direction.  That's the reason you can't lay a flat plank on a curved staircase. And its a severe problem when building a helix.

 

In your case the twist should be small enough to not matter. However I would be more concerned about putting  any turnout over a grade transition. That vertical transition curvature  is likely to be more significant. Apart from lifting wheels on rigid chassis, the necessary up/down movement of couplings in the ends on long coaches could create problems.

 

Andy

[Philou]

16 minutes ago, Andy Reichert said:

That's the reason you can't lay a flat plank on a curved staircase.

 

Oh? Can you explain the reasoning behind that - or have I misunderstood the thrust of the statement? An enquiring mind and all that ......................

 

Cheers,

 

Philip

[Philou]

@84f I don't think it stopped the 1:1 railway putting junctions on curves that are transitions on differing grades nor changes in curvature - in the case of the attached photo - reverse curves. Admittedly, the grades on the real thing are far gentler (I have the info elsewhere - just can't remember where at the mo') but I shouldn't let that stop you doing it.

 

Here's a photo showing a station throat, there being one rising grade through the station away from the camera and a change of rising grade at the transition to a steeper one. The branch line is level at this location:

 

 

Cheers,

 

Philip

[Andy Reichert]

1 hour ago, Philou said:

 

Oh? Can you explain the reasoning behind that - or have I misunderstood the thrust of the statement? An enquiring mind and all that ......................

 

Cheers,

 

Philip

 

It's a fundamental result of 3D geometry.  Imagine a large diameter coil spring with it's axis vertical. Then pull to stretch it upwards.  The spring resistance to your pull is the twisting of the wire in the coil.

 

Andy

[Philou]

@Andy Reichert I wonder if you meant a spiral staircase - but all those I've used had flat treads. Here's one I built to a curve a couple of years ago - I can tell you they were laid flat! Or did you mean something different?

 

 

Cheers,

 

Philip

 

 

[Andy Reichert]

55 minutes ago, Philou said:

@84f I don't think it stopped the 1:1 railway putting junctions on curves that are transitions on differing grades nor changes in curvature - in the case of the attached photo - reverse curves. Admittedly, the grades on the real thing are far gentler (I have the info elsewhere - just can't remember where at the mo') but I shouldn't let that stop you doing it.

 

Here's a photo showing a station throat, there being one rising grade through the station away from the camera and a change of rising grade at the transition to a steeper one. The branch line is level at this location:

 

 

Cheers,

 

Philip

 

First everything on the prototype is a far larger radius that most models. So the twist effects are far less.

 

Second, real railways have working suspension.  So the vehicles can adapt to a small amount of track twist.   However, on real railways, there has to be a decent transition distance from flat track to super-elevated track for exactly that reason. They also have similar vertical transition curvature going from flat to grades or between grade changes.

 

Andy

[Andy Reichert]

Just now, Philou said:

@Andy Reichert I wonder if you meant a spiral staircase - but all those I've used had flat treads. Here's one I built to a curve a couple of years ago - I can tell you they were laid flat! Or did you mean something different?

 

 

Cheers,

 

Philip

 

 

 

Try laying a rigid flat plank up the stairs and see if you can make it sit firmly on the edge of both step 1 and 4 at the same time.  That's what track has to do if it is climbing a curved grade.

 

Andy

 

Andy

[Philou]

Indeed, but at our scale (00/H0) the horizontal transitions are quite small (2mm approx) from the end of one sleeper to the other end. I've seen it on a 600mm radius curve and it just looked too much. In this instance less would have been better. Unless 84f is doing P4, I wouldn't bother with a horizontal transition (if he was going for one) and keep a vertical one as long as possible.  Bogie stock will have a little play so it shouldn't present a problem anyway, it's only short wheelbase wagons that might 'climb' the rail - if the change between the planes is dramatic - never had any problems with Peco pointwork on a grade - but years ago I wasn't looking at transitions in any plane either!

 

Cheers,

 

Philip

[APOLLO]

I had (note had) a crossover on a curve at the top of an incline on my O gauge N American layout, Peco O track. - it caused no end of trouble so it was taken out and track layout altered - now all OK

 

My recommendation - don't.

 

Brit15

[Philou]

Riiiiight. It's not quite the same thing. You're talking helix style developments where on our scale curves there are issues, but there again I don't think 84f is having anything on a continuous curve.

 

There is another thread elsewhere wherein issues arising from helices was much discussed:

 

 

Cheers,

 

Philip

[Andy Reichert]

11 minutes ago, Philou said:

Riiiiight. It's not quite the same thing. You're talking helix style developments where on our scale curves there are issues, but there again I don't think 84f is having anything on a continuous curve.

 

There is another thread elsewhere wherein issues arising from helices was much discussed:

 

 

Cheers,

 

Philip

 

I understand there is much discussion still at the Flat Earth society. But then they don't believe in learning geometry either.

 

Andy

[Siberian Snooper]

It is doable if it's a diesel era layout, but may well present problems for a steam era layout, due to the longer wheelbase of locos.

 

 

[84f]

Thanks all for your replies. My conclusion from the discussion, is to realign the incline, ormove the position of the crossover so it is all on the same incline plane. Instinctively, it seems to be asking for problems to  position the crossover over the transition. By which I mean the part of the incline where the gradient changes gradually from 1 in 70 to level. Thinking about the geometry of the blades in this scenario would be asking for trouble. 

For info, gauge standard is OO-SF, with a radius range of 36 to 50 inches over the cross over, up to 8 coupled RTR and compensated kit built. The cross over is for passenger traffic from the station. 

Thanks

Robin. 

 

[Harlequin]

1 hour ago, Andy Reichert said:

 

I understand there is much discussion still at the Flat Earth society. But then they don't believe in learning geometry either.

 

Andy

Andy Reichart,

The question was posed with the intention to learn from the community's response. No "Flat Earthers" here.

 

[Andy Reichert]

5 minutes ago, Harlequin said:

Andy Reichart,

The question was posed with the intention to learn from the community's response. No "Flat Earthers" here.

 

 

That's fine if you believe that the Fundamentals of Euclidean Geometry is a subject that that any RM web discussion is going to alter.

 

I would point out that a large number of folk here still believe that 00-SF geometry has no disadvantages over standard 00 for running UK RTR.

 

Andy Reichert.

[Philou]

@84f Shhhhhhhh ...................... don't mention 00-SF, the thread will now go all frothy ........... ................

 

[84f]

5 minutes ago, Philou said:

@84f Shhhhhhhh ...................... don't mention 00-SF, the thread will now go all frothy ........... ................

 

Woops, I should know better...... 

[hayfield]

1 hour ago, 84f said:

Thanks all for your replies. My conclusion from the discussion, is to realign the incline, ormove the position of the crossover so it is all on the same incline plane. Instinctively, it seems to be asking for problems to  position the crossover over the transition. By which I mean the part of the incline where the gradient changes gradually from 1 in 70 to level. Thinking about the geometry of the blades in this scenario would be asking for trouble. 

For info, gauge standard is OO-SF, with a radius range of 36 to 50 inches over the cross over, up to 8 coupled RTR and compensated kit built. The cross over is for passenger traffic from the station. 

Thanks

Robin. 

 

 

 

Robin

 

The main thing is the way you build the turnouts, making the "Set" on the inside stock rail is most important, just spend a little more time in ensuring the common crossing is built accurately and slightly take the sharp corner off the tip of the stock rail. 

[84f]

4 minutes ago, hayfield said:

 

 

Robin

 

The main thing is the way you build the turnouts, making the "Set" on the inside stock rail is most important, just spend a little more time in ensuring the common crossing is built accurately and slightly take the sharp corner off the tip of the stock rail. 

Thank you, John, that is helpful. 

Cheers. 

Robin 

[Grovenor]

You are quite right to keep the crossover on a constant grade, pointwork on a vertical curve is a nono.

 

[hayfield]

4 minutes ago, 84f said:

Thank you, John, that is helpful. 

Cheers. 

Robin 

 

Robin

 

Modelers have been hand building track since model railways were thought of, in the past without the assistance of computer generated plans and modern gauges and jigs.  Rather than issues with the track, it could be the (lack of ) flexibility in the chassis. 00 gauge is a compromise, RTR 8 coupled locos will run through much smaller radii. At worst gauge widen. 

 

If we sat back and just thought why we cannot build anything we would end up never building anything.  Good luck

[Dave John]

Hmm. 

 

Here is a curved crossover on my layout . The inner radius is a bit over 50 ". The whole thing is a bit over 3 feet long, so it's not far off the layout the op is proposing. Now I actually built it flat. EM, C+L parts . However the end of the board decided to have a warp, there is a drop of about 2 mm from about where the far signal is to the board joint at that cross wall. Call it about 1in a hundred ish. 

 

 

I had to give things a bit of a tweak at the nose of the point but now its all fettled things go through it with no problem. I can push 20 wagons back across it buffer to buffer, they all stay on despite being a complete mix of weights. All my stock is compensated or sprung, get round all this flatness thing. 

 

So 84f I'd say have a go and enjoy the build.  Might work fine, might not, but you never find out till you try.