I have come across a dispute on another modelling website regarding the above which I don't fully understand. I'm not looking to stoke the flames of what appears to be a long-standing debate but would genuinely like to know what the substance of the discussion is.
I assume that there are those who take the view that reverse curves do not represent standard prototypical trackwork practice but that they often appear on layouts in order to solve certain difficulties. What I would like to know is what the substance of the argument or arguments against having them is, again assuming that the contrary argument tends to be that modelling is for fun and that we should not get too hung up on being overly precise in setting out the trackwork.
I should be grateful to anyone who can educate me further.
The problem with reverse curves - those without a transition of at least a wagon and a half between them - is that the couplers become very misaligned. In extreme cases, at the point where the two curves meet the coupler on one wagon may (naturally) be lined up on one rail (due to the curve) but that on the next wagon will naturally try and line up on the other rail. So wagons get pulled off as the couplers try and remain connected.
If you look at the prototype you will see countless examples of what appear to be reverse curves - a simple example is the curve leading into a crossing loop - but these are significantly larger radius than anything we typically use on a layout, and if the curves are tight will always have a transition on each curve, and a length of straight track between.
In my opinion a layout which removes reverse curves doesn't look much like anything the prototype would use (at least in my experience, here in Australia) but it removes a very common reason for derailments and much heartache when trying to couple and uncouple.
This sketch shows that as the length of the vehicle gets longer, the coupler offset increases. This also applies as the radius decreases, and is more significant the further the coupler head is from either the axle or bogie centre.
(https://forum.009society.com/proxy.php?request=http%3A%2F%2Fi164.photobucket.com%2Falbums%2Fu23%2Fduttonbay%2FOdd%2520Photos%2Freversecurves.jpg&hash=39a41058d717f92782e88138d648a91e9d909b91)
You can see that with 12" radius curves and short wagons it's not so much of a problem, but even tippers can give problems when running over (say) 6" radius reverse curves.
The 20' long, 12' bogie centres represent the standard goods vehicles used on the Dutton Bay Tramway. The only 12" radius curves in use are on turning triangles, used only by locomotives. Otherwise the minimum radius is 15", and always with a transition or easement. I have no problems with reverse curves constructed in this way, even without a straight length of track between the curves.
Thank you Dutton Bay, that's extremely informative. I shall attempt to incorporate this into the construction of my own layout. Thank you for taking the time to explain it.
Here is a photo of two Liliput four wheel coaches on a reverse curve made from 2 Peco 009 12
Is the problem you refer to the reason why Pilotfriend preferred the use of 18"rad points?
The answer to that is no. 18" rad points are far easier on stock travelling through and it is easier to propell. The track also looks much more real.
I absolutely agree John. The combination of sharp curves, end-throw and the overscale clearances which are encountered all contribute to operating and coupling problems. Can't do too much with over-scale clearances unless all rolling stock is re-engineered but gentler curves will relieve the end-throw problem. Most (not all!) of the pointwork on my railway over which I regularly propel passenger stock is 18" and really does make a difference when compared with the 9" radius pointwork in sidings. Also, when designing passing loops it helps if you arrange the track geometry so that entry to the loop is a straight run and the exit is on the curved leg of pointwork. Even with my somewhat dodgy 36-year-old trackwork I can propel 14 relatively light vehicles into a siding over 18" points!
I am probably the main protagonist when it comes to commenting on reverse curves on track designs.
As Tiger (who ever that may be) has said it is actually quite easy to plan out reverse curves from a layout design.
It is also possible to adapt and modify the couplings and the rolling stock to work with reverse curves.
In practice I have found that the Peco 009 Y points that have a larger 16 inch (??) radius are just about ok if laid to form a reverse curve with almost all my stock, but it is marginal. If one coupling is slightly miss aligned then there is going to be a de-railment. I would think that the 18
Quote from: B.Meldon on November 29, 2011, 16:02
I am probably the main protagonist when it comes to commenting on reverse curves on track designs.
Noooo, surely not Brian! ;D
Personally I like the look of them and the way stock looks when negotiating them, and as I don't shunt stock I'll still use them if they take my fancy!
Quote from: B.Meldon on November 29, 2011, 16:02
"...In practice I have found that the Peco 009 Y points that have a larger 16 inch (??) radius..."
Just been looking at Peco points with a view to adding more track to my own storage yard (good grief you wouldn't think there was room but since the winter works programme I've got 12 more items of rolling stock to accommodate, never mind new locos!!!)
Anyway, the Peco website gives the radius of the 'Y' point as 18" - so don't get caught out (as I did 20 years ago when I was designing Buccabury station, by 'eck that was embarrassing!) by assuming it's 12"!!!
I am not going to go too far down this road David, but the actual tightest curve on the pre 2010 Peco 009 Y points was indeed 16 inch, but it was not consistent through the point and there were sections at the start and end of the curve that were virtually straight, so as you say when planning a layout the point in total should be considered as 18
Quote from: B.Meldon on March 02, 2012, 13:06
So when purchasing the 009 12 inch points make sure you get the newer post 2010 type not the older ones that could be old stock.
Unless using DCC as they older design are easier to covert by simply replacing the metal fishplates with insulated ones :)
Quote from: invercloy on March 07, 2012, 13:07
Unless using DCC as they older design are easier to covert by simply replacing the metal fishplates with insulated ones
How do you do that without damaging the points?
I can see how it may be posiable to slide the metal fishplates along to remove them, but fitting the insulating ones without destroying the spring in the tie bar must be a tricky job. Unless you intend to remove the spring as well and are using slow motion point motors.
Brian Meldon
Only just seen your reply, Brian.
I removed the spring and then removed the metal fishplates to replace them with insulated ones.
It's been semi successful in that they are now DCC compatible, but compared to the other points on the layout, which are all mainline ones, I'm not as happy with them. Consequently I'm removing them and replacing them with mainline ones.
I must agree that the mainline points are a better option when it comes to running. In most cases they also have a big enough radii not to have to worry about reverse curves.
However have you looked at the latest version of the 12 inch 009 points? I know that the geometry, frog, checkrail and blade pivots are improved, but I do not know if they have changed the frog wiring as well.
Brian Meldon
These are the latest version, but they don't have an updated wiring arrangement for the frog sadly.
It sounds like Peco missed a trick here then. The new versions of the 12 inch 009 points are a considerable improvement for normal DC layouts, but clearly not so good for DCC. Had they modified the 12 inch points to be the same in terms of wiring as the mainline points when they updated them they would have been good for DCC as well.
However I suppose that if Peco had modified the wiring arrangements then they would have had to announce the update and for whatever reason they chose not to do this and just updated the points without any announcement that they had done it.
Brian Meldon