This information applies to all track standards: ScaleSeven, O fine and O coarse.

The basic geometry of a fully curved switch is shown in Figure 1.


Figure 1. Geometry of a fully curved switch.


Figure 2. Flat bottom curved A switch.

The switch is carried on 15 timbers, dimension (in mm) shown on the drawing. Offset dimensions are shown against each timber.

Switch angle: 1 in 13.24 or 4°20'. To aid in drawing, the line tangential to the heel cuts stock rail 114mm before the heel H or 58mm from the toe T.


Figure 3. Flat bottom curved B switch.

The switch is carried on 14 timbers, dimension (in mm) shown on the drawing. Offset dimensions are shown against each timber.

Switch angle: 1 in 15.77 or 3°38'. To aid in drawing, the line tangential to the heel cuts stock rail 129mm before the heel H or 78mm from the toe T.


Figure 4. GWR Bull-head Curved B switch.

The switch is carried on 13 timbers, dimension (in mm) shown on the drawing. Offset dimensions are shown against each timber.

Switch angle: 1 in 15.77 or 3°38'. To aid in drawing, the line tangential to the heel cuts stock rail 110.5mm before the heel H or 47mm from the toe T.


Figure 5. Planing of curved switches.

Rail head width includes 0.22mm toe thickness which decreases linearly to zero at the end of planing. Rail foot on running side shown chain dotted. Rail foot on non-running side planed off.

This article was compiled by M. Holland for the Gauge O Guild Manual. It was adapted for the GOGWiki by Nick Baines.