Do we need 1:20 Rail Inclination

Discussion of model and prototype wheel/rail interaction.
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Martin Wynne
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Re: Do we need 1:20 Rail Inclination

Postby Martin Wynne » Thu Aug 09, 2018 7:46 am

Le Corbusier wrote:Really not sure what I'm doing ... but following your advice my set bends and knuckle bends are definitely working and I am definitely using Exactoscale chairs and definitely not using 'the proper conical press tools' :o .... :D

Hi Tim,

If there is a knuckle bend in inclined rail, the head of the rail will be going round a larger radius than the foot. That means to turn through the same angle the head needs to be longer than the foot. That means the head needs to be stretched relative to the foot, or the foot compressed in length relative to the head. There are two ways to do that. 1. make the bend using a conical mandrel while firmly holding the rail inclined and in line. 2. make an ordinary bend and then bolt each side of it down flat with the rail inclined. The prototype uses both methods, using big lumps of cast iron, shaped spacer blocks and bolts.

On the model, the chairs are made of tiny bits of soft plastic. The rails are hard metal. Guess which one wins in a fight? I'm willing to bet that where you have made knuckle bends your rail is actually vertical.

The same applies to curved plain track. If the rail is inclined, the head must follow a larger or smaller radius than the foot. It must therefore be stretched or compressed in length relative to the foot. That requires significant force, which can only be achieved using heavy fixings. A flimsy plastic chair can't do it, except at the gentlest of radii. When curved the rail will simply force itself vertical in the chairs. One of the first makes of inclined flexi-track claimed that the track was self gauge-widening on curves for this reason. In practice the vertical rail is predictable, but the effect on the gauge between the rails is not. It depends on the exact fit of the rail section in the chairs.

re. self-guiding of conical wheels. Even on the prototype this works only at gentle radii. At sharper curves the wheel is guided by the flange, which runs hard against the rail head. Hence the wear and side-cutting of curved rail, and the need for flange greasers. Were it not so, there would be no need for the wheel flanges. On a model with sharper relative curves than the prototype it has been shown that the coning has minimal effect. Try running your layout with flangeless wheels and see what happens. Image

cheers,

Martin.
40+ years developing Templot. And counting ...

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Le Corbusier
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Re: Do we need 1:20 Rail Inclination

Postby Le Corbusier » Thu Aug 09, 2018 8:57 am

Martin Wynne wrote:
The same applies to curved plain track. If the rail is inclined, the head must follow a larger or smaller radius than the foot. It must therefore be stretched or compressed in length relative to the foot. That requires significant force, which can only be achieved using heavy fixings. A flimsy plastic chair can't do it, except at the gentlest of radii. When curved the rail will simply force itself vertical in the chairs. One of the first makes of inclined flexi-track claimed that the track was self gauge-widening on curves for this reason. In practice the vertical rail is predictable, but the effect on the gauge between the rails is not. It depends on the exact fit of the rail section in the chairs.


Hi Martin ... not questioning the theory, just pleased that my track appears to be working using the plastic chairs.

I am interested by your comments on gauge through curved sections above. Presumably if the curve forces the track vertical and the correct track gauges are used then once the butanone has set things will be fine? I've noted that the butanone has a tendency to soften the chair when flooding the base - presumably this eases the process? Or do you think that in certain instances there will be a process of resetting until all settles down.

Tim
Tim Lee

martin goodall
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Re: Do we need 1:20 Rail Inclination

Postby martin goodall » Thu Aug 09, 2018 12:20 pm

I think we have been here before in previous threads.

The dynamics of the full-size railway cannot be scaled down in practice, and our wheels do not perform in the same way as wheels do on the prototype. It is misleading to refer to the behaviour of wheels in 12-inch to the foot scale, when considering the performance of our 4mm scale models.

Whatever the theory, coned wheels run perfectly happily on upright rail in 4mm scale.

My advice is to ignore the theorists, and see what works in practice. "Suck-it-and-see" is the most reliable engineering practice in small-scale model-making!

Tony Wilkins
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Re: Do we need 1:20 Rail Inclination

Postby Tony Wilkins » Thu Aug 09, 2018 5:06 pm

Martin Wynne wrote:Try running your layout with flangeless wheels and see what happens. Image
cheers,
Martin.

I actually have been daft enough to try running a wagon with flangeless wheels. If it stayed on the rails for more than about a foot it was doing well, inclined rail or not!
Re the Russian video, if only it were that simple. Wheel rail interaction is rather more complex than that as a wheel set will quickly develop a sinusoidal path along even straight track. If you have ever viewed a rake of short wheelbase four wheeled wagons at speed from a footbridge, the effect is very noticeable. At its worst hunting develops with the flanges striking the rails each side. This is most unpleasant when experienced for real.
Wheels with 1 in 40 coning and even zero coning have been tried to combat this in the past. Derby expended considerable effort developing better suspension systems to improve the running qualities of four wheeled vehicles.
For those who are wondering, as most of my track is soldered, although I do try to incline the rail inward rather than outward, I suspect most of it is near vertical to all intents and purposes.
I also doubt if the tyre surfaces of our model wheels are totally smooth having been turned. Some of mine show distinct marks from the tool tip.
Regards
Tony.
Inspiration from the past. Dreams for the future.

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Colin Parks
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Re: Do we need 1:20 Rail Inclination

Postby Colin Parks » Fri Aug 10, 2018 9:44 pm

Well, if Tony says the inclination on his track is minmal or with none at all that is good enough for me! I suspect that the Hi-nickel bullhead rail that I have been using has too square a head profile to make any benefits of inclination null.

Has anyone in an attempt to be 'getting it all right' (a slippery ethos to which I do not subscribe) ever produced pointwork where the rails are inclined at 1:20 through a common crossing, with the wing rails, point and splice all sitting correctly?! It would take some very complicated bending to achieve that - and to what practical advantage?

Tony Wilkins
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Re: Do we need 1:20 Rail Inclination

Postby Tony Wilkins » Fri Aug 24, 2018 6:13 pm

Thanks Colin.
I have been meaning to reply to this thread for a while, but was unable to find it again.
I sometimes wonder if my influence on the hobby is perhaps greater than it warrants! True, I have been involved with the hobby for a long time and have much experience particularly with trackwork, but I will be the first to admit that I do not have all the answers. When I started making trackwork, functional chairs were not an option as they are now, so I developed methods based on the best modelling practices that currently existed and built on them. Experience has been a good teacher and I have been fortunate enough to have been involved with numerous other knowledgeable individuals during several layout projects and clubs I have been involved with.
As has already been stated, when scaling down the prototype, the results are not always as predicable as one may be led to expect. In our scale the tolerances built into the full size become minuscule and probably beyond our control, therefore we have to try to achieve the best we can within those limitations and a degree of trial and error and experimentation will be needed. What works for me may not work so well (or even at all) for others, we all have different abilities.
My experience with Heckmondwike, Bodmin and Green Street, which all have / had nominally vertical rails, suggested to me that at our scale there was little to be gained from accurately inclining the rails inwards prototypically. Indeed, in some respects it can be more trouble than it is worth with the fancy bends required in turnouts and difficulties people have encountered trying to maintain track gauge. However I am willing to be proved wrong if anyone can demonstrably show an improvement in running. There are though so many different factors at play that I don't know how one would do this.
For me, the acid test will be when trains start running in earnest on Brimsdown, as with a relatively large layout and the ability to run prototypical length trains, any shortcomings are bound to make their presence known. The track will be a mixture of Bullhead and Flatbottom, hand built and flexitrack. The latter should have inclined rail, so it will be very interesting to see if there are any noticeable differences in the running between the different track sections and rail profiles.
Regards
Tony.
Inspiration from the past. Dreams for the future.

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Martin Wynne
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Re: Do we need 1:20 Rail Inclination

Postby Martin Wynne » Fri Aug 24, 2018 6:48 pm

Tony Wilkins wrote:so it will be very interesting to see if there are any noticeable differences in the running between the different track sections and rail profiles.

Hi Tony,

And interesting to see if anyone can see the visual difference. Bearing in mind that the most obvious rail ends are on check rails, which should always be vertical*. That just leaves the ends of wing rails showing inclined or vertical.

A couple of track pictures. Anyone willing to put their hand up and say that they can actually see that the rail is not at 90 degrees to the timbers?

GWR:

Image

REA:

Image

Bridge chairs more noticeable when there is a whole row of them on waybeams there.

*except for some early pre-group.

Martin.
40+ years developing Templot. And counting ...

Terry Bendall
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Re: Do we need 1:20 Rail Inclination

Postby Terry Bendall » Fri Aug 24, 2018 7:30 pm

Martin Wynne wrote:A couple of track pictures. Anyone willing to put their hand up and say that they can actually see that the rail is not at 90 degrees to the timbers?


From the angle at which the pictures are taken, probably not possible. I would have thought that you would need to see a section of rail end on to see the angle.

Terry Bendall

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Martin Wynne
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Re: Do we need 1:20 Rail Inclination

Postby Martin Wynne » Fri Aug 24, 2018 7:59 pm

Terry Bendall wrote:From the angle at which the pictures are taken, probably not possible. I would have thought that you would need to see a section of rail end on to see the angle.

Hi Terry,

That was exactly my point. The only place you are going to see inclined rail end-on is on wing rails -- which is precisely the place where it is most difficult to have model rail inclined after making the knuckle bend. Even the prototype had difficulty with that, and they had the advantage of cast iron spacer blocks and bolts. Not flimsy bits of plastic.

Also visible rail-ends on catch points, and maybe on buffer stops if the rail ends are visible under the usual grot and undergrowth. In both those cases a dedicated modeller using vertical rail could put a twist in just the visible rail end without any effect on anything. Maybe on vertical wing rails too, if careful.

Even then, it is going to take a keen pair of eyes to spot a 3-degree angle on something 75 thou high from a foot away.

regards,

Martin.
40+ years developing Templot. And counting ...

Tony Wilkins
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Re: Do we need 1:20 Rail Inclination

Postby Tony Wilkins » Fri Aug 24, 2018 8:42 pm

Martin Wynne wrote:
Tony Wilkins wrote:so it will be very interesting to see if there are any noticeable differences in the running between the different track sections and rail profiles.

Hi Tony,

And interesting to see if anyone can see the visual difference. Bearing in mind that the most obvious rail ends are on check rails, which should always be vertical*. That just leaves the ends of wing rails showing inclined or vertical.

A couple of track pictures. Anyone willing to put their hand up and say that they can actually see that the rail is not at 90 degrees to the timbers?

GWR:

Image

Martin.

Hi Martin.
What IS very noticeable is the cant or super-elevation of the track and the way it reverses from one curve into the next. Something I shall unfortunately not be attempting with Brimsdown for two reasons. Firstly, I do not wish to tempt fate with a large number of RTR converted locos and secondly much of the curved track includes pointwork. It doesn't really work in our scale anyway as the stock does not have scale inertia.
Regards
Tony.
Inspiration from the past. Dreams for the future.

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Le Corbusier
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Re: Do we need 1:20 Rail Inclination

Postby Le Corbusier » Fri Aug 24, 2018 8:49 pm

From my standpoint the main question is .... does my trackwork work.

I am using functional chairs and butanone fixing to ply sleepers. I fully accept that the rails may well be vertical where I have put set bends in and presumably also to some extent on the curves. For the rest I assume that I am at 1:20 inclinations as created by the chairs (though I hazard there will be a degree of variability here). To my unpracticed eye I can see no difference between any of the areas of my trackwork (apart from where my workmanship leaves a tad to be desired ... its a test track after all ;) )

Using the Exactoscale gauges, all is running fine and has been for a while now, so I am a happy bunny :D. The question now is whether this will remain the case when I transfer the technique onto movable baseboards and then experience changes of environment - time will tell.

So ..... a long winded way of saying, does it really matter?
Tim Lee

Tony Wilkins
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Re: Do we need 1:20 Rail Inclination

Postby Tony Wilkins » Fri Aug 24, 2018 9:04 pm

Hi Tim.
Indeed, results speak for themselves. When I think back to what model track used to look like..............................
Tony.
Inspiration from the past. Dreams for the future.

Philip Hall
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Re: Do we need 1:20 Rail Inclination

Postby Philip Hall » Fri Aug 24, 2018 9:30 pm

Hi Tony,

I’m going to experiment a little in places where it can be seen, but only with a tiny amount, just for visual effect. If it doesn’t work it will be easy to take it out before ballasting. Like you, the requirement for a lot of RTR takes precedence.

I am intrigued by the fact that sometimes quite ‘slow speed’ track has cant, but other ‘higher speed’ doesn’t. Many of the lines through Clapham Junction lean over quite alarmingly, but speeds aren’t high and on many of the lines everything stops.

Philip

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grovenor-2685
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Re: Do we need 1:20 Rail Inclination

Postby grovenor-2685 » Fri Aug 24, 2018 9:48 pm

Look at http://www.norgrove.me.uk/GWRtracknotes/R4423.pdf
You will see why the Maximum cant is commonly used on tight radius curves, the % increase in speed can be considerable.
Regards
Regards
Keith
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