Templot Club Archive 2007-2020
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posted: 10 Aug 2010 10:16 from: grog_polymer
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In the Track plan tutorial it also says that looking from the peg at Pos 0 RH refers to the direction of positive radius. This seems really bizare as a track curving to the left is considered to be Right Handed but with negative radius. I don't understand that. There are also a couple of references to shorter crossings being acceptable for turnouts with significant negative radius. Is this due to the fact that the deflection through the crossing is shallow on both roads? Regards, Greg |
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posted: 9 Nov 2010 14:43 from: Martin Wynne
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grog_polymer wrote: In the Track plan tutorial it also says that looking from the peg at Pos 0 RH refers to the direction of positive radius. This seems really bizare as a track curving to the left is considered to be Right Handed but with negative radius. I don't understand that.Hi Greg, Sorry this message didn't receive an answer at the time you posted it. All templates are handed, left-hand or right-hand. Everyone knows what this means for a turnout*, but for plain track I know it's a bit puzzling. As far as track planning is concerned, it doesn't make any difference whether a length of plain track is left-hand or right-hand. But if you insert a turnout in it, the hand obviously becomes significant. When any template is curved, if the curving is in the same direction as the hand, the radius is shown as a positive value. If the curving is in the opposite direction from the hand, the radius is shown as a negative value. For plain track this makes no difference, unless it is important to you to have the timber numbering on a specific side on the printed construction templates. For a turnout, curving it in the opposite direction from the hand is called "contraflexure" (negative curving), and the result is that the radius in the diverging road is eased. Consequently it is possible to use a shorter turnout than would otherwise be the case, without infringing your minimum radius. Here is picture of a curved crossover. In a crossover both turnouts are always of the same hand, and both of these are left-hand turnouts. But looking from the far end, the far turnout is curving to the right in the main road, so this a typical prototype instance of negative curving: http://bristol-rail.co.uk/w/images/0/03/Filton_Abbey_Wood92.jpg Image linked from this excellent site: http://bristol-rail.co.uk *Vehicles taking the main road in a conventional turnout follow a fixed straight line or ruling curve, and are able to run at line speed. Vehicles taking the diverging turnout road are deflected from their path to the left or the right, and are subject to a speed restriction as a result. regards, Martin. |
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