Minimum radii for 50mm track spacing

[DK123GWR]

I'm currently messing around with Anyrail planning nothing in particular - I'm just trying to improve my grasp of the software and track design in general. One of the layouts that I have produced uses steamline track with 50mm spacing on most of the layout. The minimum radius on scenic sections is 608mm however most of scenic track has a radius of 706mm (equivalent to radius 6) or greater, which I recall reading is enough for 50mm spacing. However, the fiddle yard would only fit if the innermost track was built to a smaller radius (572mm). At the moment, this runs parallel to a 622mm radius curve outside of it (there are a further four curves at 50mm intervals). However, I am very doubtful about whether the spacing of the 572mm and 622mm curves is sufficent to allow Mk3s to pass each other, and I'm not even sure about Mk1s (the layout is based on 1980s Slough, with a few compromises such as heavy compression of the station length and simplification of the trackwork at the start of the Windsor branch). What would you reccommend as the minimum radii separated by 50mm with modern stock?

Thanks in advance for any advice.

[Dungrange]

I'd be interested in the answers you receive, but obviously the track centre distance is determined by the type of stock that you wish to run.  The longer the stock you wish to run (eg Mark 3 coaches) the larger the radius needs to be if you want 50 mm track centres.

 

Of course the other question is whether you're just trying to avoid vehicles striking one another, or whether you're trying to ensure prototypical clearances between stock on the curves.  In the real railway you'd have about 18" (ie 6 mm in model form between passing vehicles), so the answer is also dependent on whether you want that clearance.

 

The Australian Model Railway Association produce guidance on track centres - https://amra.asn.au/wp-content/uploads/sites/7/2016/03/clearance.pdf

 

UK is in Group 3 and the calculations are apparently based on a maximum prototype vehicle length of 22.9 m and a maximum prototype width of 3150 mm.  The 00 figures are on page 7, but in my opinion, the spacing is too wide, which I think is due to the fact that 3150 mm equates to a 00 model that is 41 mm wide: most UK models are not that wide.  I'd therefore be tempted to deduct about 5 mm from the figures presented by AMRA for 00 or alternatively use the H0 figures as a guide, which means that I'd say 50 mm track centres is okay down to a radius of about 3' (900 mm) after which I'd probably look at widening track centres to more than 50 mm.

 

I have a similar issue, albeit I'm looking to use a minimum radius of 762 mm (ie 30") and I think I'll potentially be looking at something closer to 55 mm track centres at that radius.  Once I finish getting my baseboards sorted, I'll start by laying a 30" curve and doing some testing, but that won't be anytime soon.

 

To return to your specific question, I think you definitely need more than 50 mm track centres if you plan on using radii of less than 2' (ie 610 mm).

[DK123GWR]

6 hours ago, Dungrange said:

 

Of course the other question is whether you're just trying to avoid vehicles striking one another, or whether you're trying to ensure prototypical clearances between stock on the curves.  In the real railway you'd have about 18" (ie 6 mm in model form between passing vehicles), so the answer is also dependent on whether you want that clearance.

 

...most UK models are not that wide.  I'd therefore be tempted to deduct about 5 mm from the figures presented by AMRA for 00

 

So if your estimate is correct and we change the clearances from prototypical to minimal, you might just about get two Mk3s past each other at 700mm with 50mm spacing. However, I think that it is only the length of Mk3s and Mk4s which has put the UK into group 3. Mk1s sit comfortably within group 4, and so does a class 47. That would suggest you may be able to get spacings for a pre-1976 layout down to 55mm or less on 600mm radius. Of course, this may not work pre-1968 layout as you would also have to take the swing at the front of 4-6-x steam locos into account.

[Dungrange]

Yes, if using older (ie shorter stock) such as Mk 1s then you can maintain the Streamline 50 mm standard (which I think is actually 2" ie 50.8 mm) down to a tighter radius than if you are using more modern or longer Mk 3 stock.  However, as you point out, if modelling the steam era, then you'll need to allow for the greater end throw on steam locomotives with a leading bogie (compared to diesel traction), if they were permitted to operate on your line.  Therefore, as you highlight, those modelling the period from around 1968 - 1976 could possibly maintain the 50 mm spacing at a tighter radius than those modelling other eras if running the bigger stock from the period.  Ultimately it becomes very stock dependent, which is why I couldn't find an answer when I had a similar question - the AMRA data was all I could find.  If you want to run the Advanced Passenger Train (APT) then I understand you need the track spacing to be much greater at any tight radius due to the fact that the 'nose' is longer than on most other trains of the period.

 

Unfortunately, I think if you're using curves of less than about four feet and you want to use a track centre distance of less than the set-track spacing, then it's probably a bit of trial and error, which I appreciate isn't particularly helpful when drawing up plans in Anyrail.

Edited August 17, 2020 by Dungrange

[BMS]

Just to make the point which may not be relevant - while track spacing on curves may need to be say 55mm that does not apply to straights. On my layout the straights are at 50 and the curves are at 60; achieved by lengthening the outer straights by 5cm or more compared to inner adjoining curves; This also gets away from the toy train potential point that all tracks are equidistant all the time; look at the prototype. The minus is that the inner straights tend to be shorter than otherwise.

[DK123GWR]

2 minutes ago, BMS said:

Just to make the point which may not be relevant - while track spacing on curves may need to be say 55mm that does not apply to straights. On my layout the straights are at 50 and the curves are at 60; achieved by lengthening the outer straights by 5cm or more compared to inner adjoining curves; This also gets away from the toy train potential point that all tracks are equidistant all the time; look at the prototype. The minus is that the inner straights tend to be shorter than otherwise.

 It's a good idea, but in the space I allow myself on Anyrail there is more than enough variation due to the need to keep to the minimum radius for the layout while incorporating the necessary points. Station layouts also force lines to be kept close (to reduce overall width) unless there is an island platform. I have now found a way to increase the radii of the Slough fiddle yard curves (the only sub 700mm curves now are in areas with large clearances to other lines forced by the factors mentioned above). However, I feel that it would be good to keep this discussion going to see if anybody has experience in this area.

[34theletterbetweenB&D]

23 hours ago, DK123GWR said:

... any advice.

Do you have the stock to experiment with? If so lay out the curves and do it!

 

I don't want to sound too cynical, but just to start with: the inability of many to measure accurately means that unless you have real confidence in the source, it's only unsubstantiated opinion rather than useful information. Better by far to find out for yourself by experiment, then you will have data relating to your own work standard.

 

And - only my opinion - a minimum 30"/750mm centreline radius makes 'all the difference' in OO running reliability. I would sacrifice full representation of the track layout if required to adhere to this, especially if full length or nearly so trains are part of the plan.

[TonyMay]

There is a solution - which is not to run trains past each other through the curve, but to treat it as "interleaved track".  This could be achieved by simply remembering to do this; alternatively it would be possible to design a system whereby only one of the tracks could be powered at one time and the signaller has to choose between them.

[DK123GWR]

3 hours ago, TonyMay said:

There is a solution - which is not to run trains past each other through the curve, but to treat it as "interleaved track".  This could be achieved by simply remembering to do this; alternatively it would be possible to design a system whereby only one of the tracks could be powered at one time and the signaller has to choose between them.

An interesting idea which I will try to remember in case it is useful on a real layout in the future. It wouldn't work on this example though as the tracks would be used for storage.

[DCB]

I have a figure of 44.666mm as scale track spacing which works well on straight bits.   However Mk3 era is a bit of an odd ball in that the coaches overhang a long way inside the curve but have pretty average overhang at the ends on the outside.  This is a long way from the worst case scenario of a Mk 3 on the outside and a GW King or maybe an old Triang 0-4-4T running bunker first on the inside.  If the 572mm is set track it sounds like it will work but if its flexi it either won't work or won't stay put.  In the real world your 50mm can easily become 48,48, 49, 51, 53, 55 as the radius becomes sharper.