Templot Club Archive 2007-2020
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posted: 11 Aug 2010 02:19 from: grog_polymer
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I went back to the companion and had a look at the switch and crossing sections under real track. 1920_101644_010000000.jpg  What confused me is the "End of turnout curve" because I had expected the turnout to continue to curve after the entry straight. So I went back to tors and had a look at the radii and centres of entry, exit, branch and the turnout itself. I was surprised that the branch track was was not at the substitution radius but rather all track elements shared a common track centre line radius but that the branch line just had an appropriate offset for the centre of its curvature. I also played around with the entry straight length. I was also trying to get a grip on why a left or right had turnout mattered when many of the negative turnouts appear very "Y" like and I could not understand why it mattered. If I understand correctly now: a turnout has no alteration to the rail curvature along its main line but may have down the diverging path. and the stock rail for the diverging route may have a set or joggle but the main line stock rail will not. Therefore when choosing the handedness of a turnout to add, the handedness is determined by which is the main, or more main, road. And, from what I have seen, it doesn't matter what type of crossing I choose other than parallel, when I add a branch track it always gets the track centreline radius. If I use a curved crossing. The only thing that will give away its handedness will be the presence of a set or joggle in the divergent route stock rail. In preparing this, I tried all of the crossing types. When I got to parallel crossings, F4 makes both the exit and branch longer. I can add a branch track but it gives me a warning. If I try to make a separate exit track it will not let me. I had to move the peg to where I wanted the separate exit track to join, move the notch under that peg and save the template. Then quickset some plain track. Select the turnout and use peg align tools -> align the template over the background template -> facing-facing. That worked but is there an easier way? It does seem an odd distinction to prevent you creating a separete exit track on a turnout with a parralel crossing. The parralel crossing, for obvious reasons, was the only one where the branch and exit tracks are of different concentric radii. Regards and Many thanks, Greg |
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posted: 11 Aug 2010 08:44 from: Martin Wynne
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Hi Greg, If you do tools > make branch track, the branch track is given an initial radius to match the existing radius in the diverging turnout side of the V-crossing. For regular and generic V-crossings, that means the same radius as in the main road of the turnout. For curviform V-crossings, that means the turnout radius for the turnout. That is just Templot trying to be helpful and setting the most likely radius you will want in the branch track, but the expectation of course is that you will be changing it to something else. The substitution radius is a geometrical construct to help with CAD-style model track planning and allow comparison with commercial set-track turnouts. It doesn't normally correspond to any actual radius in the rails, and is seldom used when following prototypical practice for track design. The parallel type of V-crossing is something of a left-over from earlier days of Templot and I suspect is not much used now. Generally you get more control if you do tools > make return curve instead. However, it should be possible to split the exit track from a parallel crossing if it extends beyond the MRP position, and I will look at that. Thanks for drawing my attention to it. The handedness of a switch (the moving points part of a turnout) is important because it affects the speed limits through it. Vehicles travelling on the main road see no sideways deflection and can continue at the line speed. Vehicles travelling onto the the turnout road are suddenly diverted to the left or right at the switch deflection angle. For the shorter switches this is a significant deflection and there is normally a severe speed restriction over the diverging road for this reason. At the V-crossing the hand of the turnout affects the physical design of the vee. The point rail comprising the actual vee nose is normally in the main road for strength under the heaviest traffic. The splice rail attached to the side of it is normally in the diverging road. Many modellers ignore this distinction when making model vees, but some take the trouble to get it correct. Templot continues the idea of handedness into plain track, to determine the hand of the resulting turnout if you insert one in the plain track. If the template remains as plain track the hand isn't very significant, although it does affect making double track from it and the timber shoving buttons, and also which side the timber numbers are printed on the templates. regards, Martin. |
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