CANT!

[Philou]

Hello chums,

 

No, I'm not swearing or using naughty words - just trying to attract your attention.

 

In a couple of months I'm starting my layout (floor including joists to lay first) and I have some questions regarding the canting of rails on horizontal curves.

 

Do I have it correct in my mind that originally each running line was canted individually - the formation being horizontal at right angles to the track?

 

Is 'modern' practice that the formation is laid to the cant (the outer track being 'above' the inner one on curves) - if so, when did that start?

 

I assume that the cant is commenced within the transition curve length from zero to the maximum (where applicable) to 6° (approximately 6%) (or has that changed?)

 

In 00 gauge this translates to a lifting of the outer end of the sleepers to about 2mm above the inner end - this I know as I discussed this elsewhere but I cant (see what I did there?) find the topic now.

 

I have a follow-on from the above: What happens where turnouts are constructed within curves? I know it happens as elsewhere there was a discussion about mineral stock traversing from one line to another and derailed at low speed causing much damage to the sleepers within the junction. The accident report did mention that the wheel-set concerned had seized and couldn't pivot freely vertically about its axis and over-rode a rail that was canted. The other part of the accident report found that the turnout itself had been badly relaid at one time as the special chairs (I never knew about those until I read the report) to form the cant had been mis-placed and the cant mis-aligned - the seized wheel-set couldn't follow the vertical change. (Unless I'm mistaken the discussion was regarding some new cement wagons being produced by Accurascale).

 

So what happens out there in the real world? Are junctions on curves to be avoided where possible? Are heavy speed restrictions put in place where these junctions exist? Or is it as to which I alluded above that the whole formation is canted and therefore the junction is laid completely on a continuous cant without the need of special measures?

 

I ask so that I can attempt to recreate as is practicably possible a cant on the new layout - curves are not the problem - it's those pesky junctions!

 

Cheers,

 

Philip

 

Edit: Should this be in the Permanent Way topic? Apologies if it should have been.

Edited September 1, 2019 by Philou

[Miss Prism]

7 minutes ago, Philou said:

Do I have it correct in my mind that originally each running line was canted individually - the formation being horizontal at right angles to the track?

 

Usually.

 

Quote

Is 'modern' practice that the formation is laid to the cant (the outer track being 'above' the inner one on curves)

 

Usually.

 

Quote

I assume that the cant is commenced within the transition curve length from zero to the maximum (where applicable) to 6° (approximately 6%) (or has that changed?)

 

Yes, subject to cant gradient limits being observed.

 

Quote

In 00 gauge this translates to a lifting of the outer end of the sleepers to about 2mm above the inner end - this I know as I discussed this elsewhere but I cant (see what I did there?) find the topic now.

 

No. Cant does not scale. A model 2mm cant to implement a 6" prototype cant will be 76 times more than it should be. (for 4mm scale)

 

Quote

What happens where turnouts are constructed within curves?

 

The whole bed might be canted, or the differential between running lines lessened, in those cases. 

 

Quote

Are heavy speed restrictions put in place where these junctions exist?

 

Of course.

 

[daveyb]

Another thing to consider if putting a prototypical cant on model track, is that you will need prototypical compensation (or at the very least freedom of movement - slack or slop in real terms) on all model rolling stock.  Otherwise it will likely just derail as it would on poorly laid flat track. 

 

This may be helped by smooth transitions but no doubt the length of run is going to be compress, therefore the rate of change in the outer elevation will increase and though that may not in itself look unrealistic or cause running issues, it will accentuate the compression of the overall length and tightness of radii.  You may end up with trains lurching into the curve (or seeming to) where a smooth transition was the designed aim

[AberdeenBill]

38 minutes ago, Miss Prism said:

No. Cant does not scale. A model 2mm cant to implement a 6" prototype cant will be 76 times more than it should be. (for 4mm scale)

 

 

Surely it does?   A 'full size' cant-angle of 6 deg for 1435 mm rail separation will have the outer rail 1435 mm x sin(6) = 150 mm = 6 in higher.    For 16 mm (OO gauge), 16 x sin(6) = 1.7 mm or for P4, 18.83 mm x sin(6) = 1.97 mm.     Or am I (quite likely) missing something? 

 

Bill

 

[Andy Hayter]

48 minutes ago, daveyb said:

Another thing to consider if putting a prototypical cant on model track, is that you will need prototypical compensation (or at the very least freedom of movement - slack or slop in real terms) on all model rolling stock.  Otherwise it will likely just derail as it would on poorly laid flat track. 

 

 

 

Not sure where this idea  has come from but I have not had problems of the type you describe.  The tendency of any item of stock entering a curve is to go straight on.  The outer rail stops this happening - unless you go into the curve at a very unrealistic speed - it's why train set operations come off at the curves.  Adding a cant makes it more difficult for the item of stock to go straight on.  

 

I have done this very unscientifically on 3ft ruling curves.  The track is laid on 1/16th cork.  The 1 - 2 foot before the curve has an added second strip of 1/16th cork at the outside and the curve itself has two strips of 1/16th cork round the outer curve.  The track is allowed to find its own transitions into the abrupt change of cork support.  Result - smooth running even at silly speeds. [I run TGVs so silly speeds are semi-prototypical.]

[Philou]

Thanks for all the replies.

 

Regarding the scaling of cant, I'm with AberdeenBill regarding the mathematics, though probably the cant may looked skewed at 4mm scale due to the very tight and non-prototypical curves that we end up using on our layouts. I've seen it done on a curved module of about 600mm radius with a 2mm raising of the outer rail, though 'correct' it did look a little overdone - hence perhaps the scaling effect to which alluded Miss Prism.

 

Cheers,

 

Philip

[Miss Prism]

The differences between running rails in the various 4mm scale track systems is not significant. Cant doesn't scale according to the scale factor, because cant is proportional to the square of the speed:

 

cant = GV^2/gR

 

(where G is the gauge, V is the velocity, g is the gravitational acceleration, and R is the curve radius)
 

The physics is the same - the devil is in the numbers.

 

[Andy Hayter]

29 minutes ago, Andy Hayter said:

 

Not sure where this idea  has come from but I have not had problems of the type you describe.  The tendency of any item of stock entering a curve is to go straight on.  The outer rail stops this happening - unless you go into the curve at a very unrealistic speed - it's why train set operations come off at the curves.  Adding a cant makes it more difficult for the item of stock to go straight on.  

 

I have done this very unscientifically on 3ft ruling curves.  The track is laid on 1/16th cork.  The 1 - 2 foot before the curve has an added second strip of 1/16th cork at the outside and the curve itself has two strips of 1/16th cork round the outer curve.  The track is allowed to find its own transitions into the abrupt change of cork support.  Result - smooth running even at silly speeds. [I run TGVs so silly speeds are semi-prototypical.]

Thinking about it the cork may have been 1/32 and not 1/16th but the comment remains the same.  Difficult to now measure.

[Fat Controller]

10 hours ago, Philou said:

 

 

I have a follow-on from the above: What happens where turnouts are constructed within curves? I know it happens as elsewhere there was a discussion about mineral stock traversing from one line to another and derailed at low speed causing much damage to the sleepers within the junction. The accident report did mention that the wheel-set concerned had seized and couldn't pivot freely vertically about its axis and over-rode a rail that was canted. The other part of the accident report found that the turnout itself had been badly relaid at one time as the special chairs (I never knew about those until I read the report) to form the cant had been mis-placed and the cant mis-aligned - the seized wheel-set couldn't follow the vertical change. (Unless I'm mistaken the discussion was regarding some new cement wagons being produced by Accurascale).

 

So what happens out there in the real world? Are junctions on curves to be avoided where possible? Are heavy speed restrictions put in place where these junctions exist? Or is it as to which I alluded above that the whole formation is canted and therefore the junction is laid completely on a continuous cant without the need of special measures?

 

I ask so that I can attempt to recreate as is practicably possible a cant on the new layout - curves are not the problem - it's those pesky junctions!

 

Cheers,

 

Philip

 

Edit: Should this be in the Permanent Way topic? Apologies if it should have been.

When other lies join canted lines, there is an element of 'twist', which is supposed to be carefully measured, and inspected regularily. There were a number of instances in the Midlands where this hadn't been done, on sidings joining the main line; there were several derailments in which  twist at the limit of permitted tolerances was cited as one of the causes. When wagons with suspensions at the their limits  encountered this, derailments occured. There are RAIB reports on at least two such incidents, at Landor Street and Washwood Heath. In the former, the situation was further aggravated by an unevenly-loaded container; this caused 'flange-climb'. 

[Trog]

The special baseplates mentioned are called two leveled and have a thicker than normal base, they used to be measured in 1/8ths of an inch but have now gone metric. The use of these baseplates allows you to have different cants on two tracks attached to the same timbers. So for example you can start a transition to reduce the cant on a straighter diverging line right off the crossing while the mainline cant is provided by the rake of the supporting timbers.

 

The largest cant used in this country is I believe 8" but this is exceptional and only used in a couple of places, the normal maximum of 6" is however quite common.

[Pete the Elaner]

9 hours ago, Andy Hayter said:

 

Not sure where this idea  has come from but I have not had problems of the type you describe.  The tendency of any item of stock entering a curve is to go straight on.  The outer rail stops this happening - unless you go into the curve at a very unrealistic speed - it's why train set operations come off at the curves.  Adding a cant makes it more difficult for the item of stock to go straight on.  

 

I have done this very unscientifically on 3ft ruling curves.  The track is laid on 1/16th cork.  The 1 - 2 foot before the curve has an added second strip of 1/16th cork at the outside and the curve itself has two strips of 1/16th cork round the outer curve.  The track is allowed to find its own transitions into the abrupt change of cork support.  Result - smooth running even at silly speeds. [I run TGVs so silly speeds are semi-prototypical.]

I tried it many years ago & got it wrong.

The issue was not going from flat to cant, but from cant back to flat again. The bogie needs to twist on the chassis. Most locos (it was a diesel layout) were fine but I had re-bogies some coaches & there was no enough twist with these. As the cant dropped away the rear bogie & which was still on the cant. kept the outside of the front bogie in the air & derailed it.

My errors were that the transition from flat to cant was not gradual enough & I did not allow for the lack of flex with the re-bogied coaches.

If anyone is considering doing this for the first time, please do not repeat these errors.

[Edwin_m]

Cant on a model is purely for cosmetic effect, it doesn't help the trains go round curves (and it can hinder if the stock is uncompensated and the cant gradients are too abrupt).  Because gravity doesn't scale, model trains can go happily round curves at speeds where the prototype would overturn. 

 

Generally speaking modern curves will be canted independently - that is that the lower rails of each track will be level with each other, rather than being in a common plane so the outer track is higher than the lower.  This may not be so if there is a crossover or other pointwork on the curve between the two tracks in question, but that sort of layout is avoided where possible as it's difficult to maintain and may cause a lower speed restriction for trains on the principal route.  If a junction on a curve is optimised for trains on one route, then those on the other route may encounter reduced or even negative cant, which will lead to a severe speed restriction (Sheet Stores Junction springs to mind). 

[doilum]

Somewhere in the magazine archives lies a major article on the subject. I think it predates MRJ and is probably from Model Railways around the time that Heckmondwyke was under construction.

[teaky]

31 minutes ago, Pete the Elaner said:

I tried it many years ago & got it wrong.

The issue was not going from flat to cant, but from cant back to flat again. The bogie needs to twist on the chassis. Most locos (it was a diesel layout) were fine but I had re-bogies some coaches & there was no enough twist with these. As the cant dropped away the rear bogie & which was still on the cant. kept the outside of the front bogie in the air & derailed it.

My errors were that the transition from flat to cant was not gradual enough & I did not allow for the lack of flex with the re-bogied coaches.

If anyone is considering doing this for the first time, please do not repeat these errors.

Can you remember any of the dimensions?  What were the radius of the curve, the degree or height of cant and the length of transition?  It might be useful to know what didn't work for you.

 

I was, coincidentally, looking into cant only yesterday and had come around to thinking that I would be safer avoiding it unless I could find examples (for 00 gauge with uncompensated chassis) where it had been used successfully.

[Pete the Elaner]

Just now, teaky said:

Can you remember any of the dimensions?  What were the radius of the curve, the degree or height of cant and the length of transition?  It might be useful to know what didn't work for you.

 

I was, coincidentally, looking into cant only yesterday and had come around to thinking that I would be safer avoiding it unless I could find examples (for 00 gauge with uncompensated chassis) where it had been used successfully.

It was around 30 years ago at a club I used to belong to, but I will try to recall it as accurately as possible..

 

The coaches which derailed were Hornby & Lima Mk1s on either Replica or Westward commonwealth bogies. Modern Hornby Mk1's will be different.

I used matchsticks for propping up the outside of the track at about 3" intervals. These were from a kit builders bag rather than from a box of matches, but they looked about the same size. I have just measured a real match & it is about 2mm in width. For the transition, I cut some matches in half, about 2 at each end, then relied on the rail itself to make the step a bit smoother. It looked ok & only the modified Mk1s 

I did not really have a chance to troubleshoot this because I went to Uni. When I cam back from my first term there, 2 new members at turned up at the club & were now "working" on the layout. Destroying it would have been a better description than working on it because they made a right mess of what I & the others had done.

[njee20]

I slapped some 1mm card strips under the outer edge of the sleepers on my N gauge layout, with no thought to transitions or anything!

 

The effect is subtle, but IMO it works, I’ve never had any stock derail at the transitions (just everywhere else!).

 

Untitled by njee20, on Flickr

 

I can’t understand the notion that it doesn’t scale, of course it does. If 2mm would be 76 times too much, @Miss Prism are you suggesting the correct amount would be 0.026mm...?

 

 

[Miss Prism]

1 hour ago, njee20 said:

I can’t understand the notion that it doesn’t scale, of course it does. If 2mm would be 76 times too much, @Miss Prism are you suggesting the correct amount would be 0.026mm...?

 

Yes.

 

Example: a prototype half-mile radius 65 mph curve has an equilibrium cant of approx 150mm. The equivalent 10.5m model radius curve has an equilibrium cant at 0.38m/sec (65 smph) of only 0.025mm.

 

i.e. model cant does scale, and indeed it scales linearly, but it scales in proportion to the reciprocal of the scale factor, e.g. 1/76 for 4mm scale.
 

Edited September 2, 2019 by Miss Prism
spellink

[APOLLO]

Points on superelevated curves are a pain for the real railway also .

 

Read this report on a derailment (thankfully at low speed) of a freightliner at Wigan North Western in 2009

 

http://www.railwaysarchive.co.uk/docsummary.php?docID=3509 

 

Click on the pdf at the top for the interesting story. A few things involved, curve too sharp, no check rail, change of cant direction - all relevant also to model railway track. (page 17 paras 45 & 46). A twist in the wagon frame didn't help either.

 

Brit15

 

 

[Colin_McLeod]

I think the dilemma is that if one calculates the cant as an aid to train running, then because it is a function of the square of the speed, the calculation gives the smaller cant that Miss Prism is referring to.

 

If however, one ignores the dynamic equations and merely wants to scenically reproduce a model of the prototype cant then the 6" cant can be visually represented on the model by a 2mm cant even though it is higher than required mechanically.

Edited September 2, 2019 by Colin_McLeod
Auto correct going mad and can't handle cant.

[Allegheny1600]

25 minutes ago, Miss Prism said:

 

Yes.

 

Example: a prototype half-mile radius 65 mph curve has an equilibrium cant of approx 150mm. The equivalent 10.5m model radius curve has an equilibrium cant at 0.38m/sec (65 smph) of only 0.025mm.

 

i.e. model cant does scale, and indeed it scales linearly, but it scales in proportional to the reciprocal of the scale factor, e.g. 1/76 for 4mm scale.
 

I rather think you're being needlessly pedantic here!

Surely the required term is actually superelevation? Or, banking (though I'd have that that was more a motor racing term!).

Many, many model railways have such a thing as we have seen examples of above.

The physics may be different but the visual effect is what is really required.

[Titan]

27 minutes ago, Miss Prism said:

 

Yes.

 

Example: a prototype half-mile radius 65 mph curve has an equilibrium cant of approx 150mm. The equivalent 10.5m model radius curve has an equilibrium cant at 0.38m/sec (65 smph) of only 0.025mm.

 

i.e. model cant does scale, and indeed it scales linearly, but it scales in proportional to the reciprocal of the scale factor, e.g. 1/76 for 4mm scale.
 

 

But in the model world, we are not trying to replicate the effect of cant, we are trying to replicate the look of cant.  Therefore  the equilibrium cant and any other calculations are irrelevant. If the full size has 150mm of cant, then the model will need approx 2mm of cant to look the same, irrespective of the effect on the rolling stock running over it.  

[njee20]

Ah yes, I would have thought that was patently obvious that people were talking about the appearance, not the effect.

[Andy Hayter]

As Titan suggests, unless you are modelling in P4 or similar finescale standards, the introduction of cant is entirely cosmentic.  Overscale flanges will keep stock on the track where in real life it would fall off.  That is why of course we can use unrealistic curves.

[Philou]

I was looking at this question of cant purely from an aesthetic point of view rather than the dynamics. The one station that I propose modelling is that of Pontrilas (now swept away à la Beeching). Old photographs clearly show trains at rest picking up/setting down stopped on the curved platforms and are most definitely canted.

 

Those that are in the know, is there an approximate date when there was a changeover from individual canting of tracks to when the formation itself was canted? I'm not proposing to model any HS1 or 2 track - just an enquiring mind and all that.

 

Cheers,

 

Philip

[teaky]

Sorry Philip.  I apper to have inadvertantly hijacked your thread.  Please can I encourage people to answer Philip's question as a priority, rather than my supplementary question regarding what cant characteristics work in model form.