Some information and research on designing Curved platforms

As part of my new project, the issue of modelling curved platforms came up so I've headed off to research some background.

Some Useful Dimensions for Modellers building Platforms.
 I cannot reproduce a most helpful diagram and topic which I've found, but here is the link including every useful dimension (at scale) you'll ever need for platform designs at N, OO and EM gauge.

Platform Modelling Dimensions

 
Dimension "Y" helpfully told me that the gap between inside of rail and platform edge must be>= 11mm at OO scale.Dropping this into Anyrail, used as a handy CAD device I got the upper result for a straight platform.




Surprised by how close this places a standard Coach (Collett Bow end) to the platform edge I went off searching some photos on line to confirm. Would you believe it, most I found were at stations with curving platforms.

Take #2 - went to my holiday pics from the SVR, same result! Seems curved platforms are quite common after all!
However photos at both termini suggested coaches do stand that close on straight platforms.

The lower section of the image shows a 2000mm radius curve (152m real life) with the centre of coach correctly distanced. At the ends the gap is about 1ft for your live passenger which does not seem a great span to cover when moving upwards. The useful lesson for me was that I'd grown too comfortable with adopting a tighter radius in my design without checking the data so thanks are due for helping me to a working solution.

This shows my "home" station of Weston-super-Mare with its own 250m radius track which makes a full 100+ degree turn from entry to exit of the area



'Reproduced with the permission of the National Library of Scotland' (with additions)
https://maps.nls.uk/index.html

Hi Colin

Thank you for the info and link.

Your efforts remind me of the problems I have encountered over the years building curved platforms.

My latest challenge has been that recent carriages I have bought have been progressively longer (more modern?). Which means I have to shave more off the platform edge :-)

Cheers
Evan

In model form. we have to allow greater gaps because of the more usual sharper than scale curves. There are a number of techniques for creating sufficient clearances on model platforms.

The easiest is to use the longest and widest possible stock items with pencils taped to their centre and outer extremities. In my own case, I used BR mark 3 coaches from an HST and a Bachmann Networker Turbo class 166 driving car, these being wider than the mark 3, even.

There are always the odd items of rolling stock that will trip one up. I found the ladders on the Kernow/Dapol Silver Bullet china clay tanks were over-width and had to be trimmed back slightly by removing less than 1mm from the locating tabs at the backs of the ladders at solebar level. Likewise, Heljan's Cargowaggon vans had over-width centre steps. These had to be trimmed back approximately 1mm on each side.

Colin has seen my curved platforms on my Underground section, but here is an early photo of it still under construction., to illustrate part of the process. They still required slight additional trimming before being able to be used fully in service.

Interesting stuff Colin.

I went for 218/220 inch (just over 18 feet) radius for my platforms at Yarslow with a bit of 60/62 inch at one end (double track 2 inches apart).  The dimensions were determined by inserting a piece of track in AnyRail between the two ends, hitting "Smooth Curve" and then matching it with curves (easier done than described).

To help lay the curves, I have made a template at 220 inch radius.  It looks dead straight until you put a Mk I next to it when it looks decidedly curved!  The "1 foot at the end" step is interesting - I will have to re-visit my curves to see how they compare.

My old Yarslow layout used 36 inches through the platforms - I thought that was going to be ideal but in reality, it was way too little.  Below is a picture taken during the construction stage in 2015 (Mk I non-corridor "suburban" stock in the platform).



David Jenkinson always said that sharp curves look better from the inside.  I got away with the sharply curved platforms by not being able to look along them from a normal viewing angle and I am using that excuse again on the new layout!

Thanks for sharing the info and thoughts.

Barry

Thinking some more about this problem, I realised it's just basic Pythagoras.

For any Radius of track (r), coach of length (L) if the centre of the coach is placed correctly at your desired platform separation, then the deflection away from the platform by the end of the coach is defined as (a) where:

a = r - (r^2 -(L/2)^2)^0.5  (note ^0.5 = sq root)

or if you'd prefer to define the distance between the mid-point of the coach and the end door as (m)

the same formula simplifies to:

a = r- (r^2 -m^2)^0.5

To give you two worked examples:

1) my setting with 2000mm radius, Coach 220mm
a = 2000 -(2000^2 -110^2)^0.5
a = 2000 - 1997

a = 3mm - the extra separation at coach end (= 9" extra separation to that at centre - lifesized)

2) Barry's 18' radius with 12" coach
a= 18 - (18^2 - 0.5^2)^0.5
a = 0.08" i.e. 80 thou

 If anyone would appreciate a simple Excel file I can upload one.


Addition: See post 7 for comments regarding platforms outside the curve.

 
 

Hi Colin

Thanks for expanding this further.  I can't help but think that 80 thou will present its own problems given that the wheelsets probably have more than that as sideplay!

Once again the forum throws up information, thought-provoking content, expertise and challenges.

Long may it continue!

Barry

Barry,
I think you might have misunderstood my note.

In my diagram you see a perfect matching circular arc used as the platform, the 80 thou is the extra gap occurring at the end of your coach. It is distanced from the platform not coming closer if the platform is on the inside of the curve as shown.

 For a platform on the outside of the curve, you can adjust the separation at the mid point of a coach so that the end does not create a problem. In effect the extra 80 thou gap is transferred to the mid point of the curve, nothing material.

You will of course need a curved platform of suitable radius in either case.
 
Colin

Thanks for clarifying that Colin.  It is clearly one of those things that is easier to deal with in the flesh rather than to explain!

Barry