Templot Club Archive 2007-2020
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posted: 27 Sep 2008 16:02 from: Hayfield
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Please could some one help with terminology please, where the description is for a seven foot switch, does that relate to the switch length and not the crossing angle. If so what is the difference between a switch having a title in feet and a switch being described by a letter (A, B etc). Thanks in advance. John |
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posted: 27 Sep 2008 16:39 from: Martin Wynne
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Hayfield wrote: Please could some one help with terminology please, where the description is for a seven foot switch, does that relate to the switch length and not the crossing angle. Hi John, A switch is the portion of a turnout comprising the moving point blades, not the entire turnout, like this: startup_pad.png  The switches which are designated by length in feet (9ft, 12ft, etc.) are loose-heel switches (meaning that the point blade pivots when it moves). The quoted length is either the actual length of the point blade to the pivot. Or it's the length measured to a designated geometrical heel position a little way back from the actual pivot. The switches which are designated by letter sizes (A, B, etc.) are flexible switches (meaning that the point blade is fixed tight at the heel and bends when it moves). These are the well-known sizes used for most standard-gauge track in the UK since about 1925. But for light railways, narrow-gauge and industrial tracks, you should normally use the loose-heel switches instead. Also the old loose-heel switches remained in sidings and yards and on branch lines for many years after 1925, often remaining until the line closed. The letter designations were introduced by the Railway Engineering Association after the grouping of railway companies in 1923, so the bullhead letter sizes are often called "REA switches". The GWR introduced their own design of flexible switches instead in 1930, but used the same letter designations. There are some more notes and diagrams about all this at: real track page in Templot Companion regards, Martin. |
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posted: 27 Sep 2008 18:14 from: Hayfield
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Thanks Martin for clearing that up. John |
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