Radius and Curves

[GNRi1959]

In planning a small layout and was wondering how much do I have to pay attention to the standard radius of my curves on corners. 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 using a trammel 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?

[David Holman]

Now there's a can of worms, Tony!

I have no knowledge of set track, other than the curves will be visually tight unless short wheel based stock is used. In 4mm scale, a minimum radius of 3ft/900mm is usually deemed appropriate, not least to avoid buffer locking when propelling stock - though tension lock couplings will prevent this of course. However, it should be possible to use radii down to 750mm with care and things still look/work ok.

 Even 900mm radius is incredibly tight in prototype terms, but compromises have to be made when space is a premium. However, one thing to investigate will be 'transition curves'. In other words, start with a gentler radius and gradually tighten it as the curve develops. It will prevent sudden changes of direction as stock takes the curve, but also require the use of flexitrack - though this should be no harder to lay than set track. Get the latest Peco, or use SMP or C&L & it will look better too - even if you go with the dreaded 16.5

 I believe templates for making transition curves are available commercially.