... . I understand the external geometric radius is the substitution radius of the turnout. What's the internal geometric radius? Hi Nigel, see: topic 397 The internal geometric radius is a single arc between the the main road and the V-crossing. i.e. similarly to the external geometric radius it disregards the switch deflection, planing, etc., and also any crossing entry straight for a regular V-crossing. It is the same radius as for a gaunt turnout with zero gaunt offset and a generic V-crossing: 2_090726_270000001.png It's important to note that the geometric tangency positions do not normally coincide with any fixed position in a normal turnout. For a "natural"-size turnout (such as this B-8) the tangency position is normally beyond the switch front: 2_090726_270000000.png For other turnout sizes it may be within the switch front. cheers, Martin. posted: 9 Jul 2018 20:42 from: Nigel Brown Thanks Martin Clarifies things nicely. Nigel Parts of Templot Club may not function unless you enable JavaScript (also called Active ...