Question Regarding Track Radius Measurements

[amw15]

Hi guys,

A quick question which I have been pondering for some time - where is the radius of a curved track measured to, i.e. when the radius of a track is described as (say) 24'' is that 24'' to the inside rail or the middle between the two rails?

Thanks 

[GraniteRailroader]

I have always based it upon the centerline of the track from a specified point.

[selector]

Agreed...the centerline.

[Union Pacific Cascade Division Model RR]

I'm getting ready to put in a new layout and will be measuring to the inside.

[amw15]

Hmmm...I also have always thought that it would be the centerline, but having given it some more thought, in the instance of quoting a minimum radius wouldn't the minimum be the radius to the inside rail not the centerline?

[GraniteRailroader]

Yes, the inner rail will have a slightly tighter radius. The outer rail will have a slightly wider radius.

[grayfox1119]

As others have stated, if you use the inner ( closest ) rail, the radius will be slightly less and the outer ( furthest ) rail will be slightly more. Therefore, the logical and correct way to set the track is to use the midpoint which is of course the centerline between the tracks.

[tomikawaTT]

The stated radius (in the specification block of a published track plan, for example) is measured at the track centerline.  For proof, put together a semicircle or full circle of 18" radius sectional track and lay a yardstick across it.

That does not mean that it isn't possible to 'fudge' a little to make your tracklaying easier.  After determining that the flex track I'm using has 28mm ties, I've taken to marking my radius at 624mm - 24 inches plus 14mm (1/2 the tie length.)  It's a lot easier to line up the ends of the flex track ties on a clearly visible line than it is to try to find the centerline - especially under a layer of grey latex caulk.

Chuck (modeling Central Japan in September, 1964)