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Layouts and Curve Radius


Guest ConventSiding
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Guest ConventSiding

In planning a small layout, how much do I have to pay attention to the standard radius curves. If I am working on a circuit do I set it out strictly sticking to the printed dimensions that manufacturers show for 1st-2nd-3rd radius curves at all or do these apply to set track only. Might seem like a daft question but if points have a specific curve radius surely they sit best in that curve also?

 

Obviously the actual layout will make its way through stations and sheds but my question relates more to corners of my baseboards.

Edited by ConventSiding
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In planning a small layout, how much do I have to pay attention to the standard radius curves. If I am working on a circuit do I set it out strictly sticking to the printed dimensions that manufacturers show for 1st-2nd-3rd radius curves at all or do these apply to set track only. Might seem like a daft question but if points have a specific curve radius surely they sit best in that curve also?
 
Obviously the actual layout will make its way through stations and sheds but my question relates more to corners of my baseboards.
 
 
Hi Tony
There are no rules as such. Most layouts are nearly always constrained by space so scale track arrangements, distances and scale radius are not possible and compromise is needed to make a scaled down version look right.  The track numbers may not be to scale but with clever placement of scenery and good ballasting it can look like the real thing. You do not need to pay attention to manufacturers set track radius, but a few tips if possible. 
  • Laying flexitrack try and keep to 3rd radius or higher if possible 
  • constant radius throughout a 90 degree bend is best if possible. 
  • 1st/2nd radius curves can often be used out of sight to fit a tight bend in a hidden section (i.e. Behind back scene after going under half a virtual bridge or tunnel entrance, or under upper base boards or hills at corners. 
  • Set track points and curves force wider gap between tracks. Avoid all set track like the plaque. 
  • You can change the radius of a curve gradually but the change works best if it is a constant rate of change. 
  • it is nice if the radius of track work joining points initially matches the radius of the point for a visually smooth join which can tighten afterwards. There is nothing worse looking than abrupt angular kinks when one point joins another or track joins a point. I've seen more than a few fabulous layouts ruined by this. 
  • Dry assemble the track using tacks to see if it 'looks right' and curves flow into each other with constant radius at joins, or at least constant rate of change in curves. You can tweak and make adjustments before committing to ballast which will fix it forever. 
  • If you are forced to have some sharp bends, try disguising them with partial scenic breaks like behind a few trees, buildings, bridge, etc.
  • If laying twin track around bends ensure track gaps support your longest rolling stock (e.g. Coach ends over hanging track don't snag other passing coach ends)

 

Hope these few suggestions help. If it looks right it is right, don't be constrained by numbers. 

Edited by NoelG
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I would disagree with some of what Noel says, or at least think that some clarification/further detail might be useful:

 

Laying flexitrack try and keep to 3rd radius or higher if possible

 

To put it another way: if you have to have curves tighter than about 2ft radius (3rd radius is ~18") then think seriously about using Setrack.  It can be difficult to get flexi to bend smoothly at small radii, and to get it to stay that way.

 

Constant radius throughout a 90 degree bend is best if possible

 

I'm not sure if this is referring to a general principle, or just to the use of Setrack.  If the first then it's simply wrong: real railways use transition curves to avoid the sudden change of direction you get going from straight track (which is effectively a curve of infinite radius) to a fixed radius curve.  Transition curves in flexi are good on a layout as well, if they can be accommodated in the space available.  (Do not try to use transition curves if the radius required for space reasons is already tight - you'll end up having an even tighter radius at the apex of the curve, and there's a risk that some of your stock won't like it.)  I'd suggest that it's best to use some decent track planning software that understands transition curves if you find yourself contemplating this (IIRC Xtrckcad does understand transition curves; AnyRail doesn't).

 

If the advice was relating to Setrack then I would still disagree.  It's perfectly possible to mix Setrack radii through a curve eg using one 4th radius curve or even the 860mm radius 'special curve' as an approximation of transition curve.  There's no need for "abrupt angular kinks" if you take the appropriate care in laying the track (and it's just as easy to get kinks if you are slapdash with flexi).  I cite in evidence my last layout, during the track laying phase, which used short Streamline turnouts (nominal radius 610mm) combined with 2nd and 3rd radius curves:

 

gallery_23983_3473_31444.jpg

 

I'd suggest that it's far from easy to tell at first or even second glance which Setrack radii were used where.  Others might disagree.   Unfortunately I don't have any video of stock moving on this layout (and it's been dismantled since the photo was taken) but I can assure you that trains traversed those sections perfectly smoothly.  In fact, the larger radius of the Streamline points was quite effective as a 'transition' into the tighter radii of the Setrack.  Note also that, by careful use of varying curve radii and a few short inserts of straight track, the track separation on the curves was closer to the Streamline 52mm separation than the significantly over-large 67mm of Setrack (and bogie stock could still pass on the curves with no problem whatsoever, as you'd expect).

 

Set track points and curves force wider gap between tracks. Avoid all set track like the plaque.

 

I'd agree that Setrack points are best avoided in anything that aspires to be more than 'just' a train set (they have other drawbacks as well, like their tight radii and dead frogs).  As explained above, though, Setrack curves can have definite benefits if space constraints demand curve radii under ~2ft.  Even Setrack straight track can have benefits in that it's easier to lay dead straight, if that's what you want/need.  The rather ugly sleepering at the ends of Setrack sections becomes more or less unnoticeable when the track is ballasted (or you could even just cut off the ugly inch or so at each end).

 

it is nice if the radius of track work joining points initially matches the radius of the point for a visually smooth join which can tighten afterwards. There is nothing worse looking than abrupt angular kinks when one point joins another or track joins a point. I've seen more than a few fabulous layouts ruined by this.

 

As noted above, I'd argue that 'abrupt angular kinks' are a result of careless track laying rather than any inherent problem with mixing radii in curves.  Yes, in a perfect world smooth transition curves are the ideal, at least in plain track.  But if space constraints have to be met (and the OP did specifically state that the context of their question was the planning of a small layout) then compromises need to be made - and IMO judicious use of Setrack is one of those compromises.

 

If the OP would like to review past discussions on this topic I'd refer them here, here, here and here for starters.  After that Google is your friend...

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Sure, to be specific my general point is if possible avoid less than 2ft radius, but agree if a few tight bends needed (e.g. 3rd radius) then they can be visually disguised with scenery and semi scenic breaks to make 90 degree turns.  When space is tight there isn't always the room for transition curves, but I agree they look better (i.e: transition - 'you can change the radius of a curve gradually but the change works best if it is a constant rate of change').  

 

"I'd argue that 'abrupt angular kinks' are a result of careless track laying"  

 

Agree 100%

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Guest ConventSiding

ejstubbs and NoelG, I welcome both your replies.

The addition of a photograph always helps. I measured the space I have inside the shed and I see no reason why baseboards similar to those shown above aren't ample. Provided there is a continuous loop I don't need wide sections, I like the space inside to be plenty as I have a small workshop table there for scratch building. I will set the curves out on large drawing paper and tease out the various ideas I have. I wanted to replicate our local station but it has proved to be impossible. However, there are aspects of the engineers drawing I can extract to give endless hours of fun, both running out of the station and shunting in the yard.

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