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                                       'Slewing' curves
     
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1st message | this message only posted: 26 Jan 2018 16:52
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from:
johndon
United Kingdom

 

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Apologies in advance if slewing isn't the correct term but I'm gradually getting to grips with Templot and have a question about the following plan:


Based on the map, it appears that the track needs to be 'dragged down' in the centre to conform with the plan but I can't for the life of me figure out how to do this?

John

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2nd message | this message only posted: 26 Jan 2018 17:08
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from:
Martin Wynne
West Of The Severn, United Kingdom



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Hi John,

For that you need the swell mouse action. See:

 http://templot.com/companion/swell_function_ctrl_f10.php

Looking at your plan it is probably not a single radius. Instead of using swell you could start with the turnout, make branch track from it, curve the branch track to the line, and then make transition to the existing straight track.

For an example of this process, see:

 http://templot.com/companion/link_existing.php

That keeps everything aligned, whereas swell takes the ends of the template out of angular alignment with adjacent templates. Swell is normally used on an isolated template which is not aligned with any others.

cheers,

Martin.

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3rd message | this message only posted: 26 Jan 2018 17:12
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from:
johndon
United Kingdom

 

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Thanks Martin, much appreciated.
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4th message | this message only posted: 26 Jan 2018 17:17
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johndon
United Kingdom

 

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I see what you mean about just using swell, it gives rise to this effect when the line goes straight, I shall try your other suggestion, thanks again.


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5th message | this message only posted: 26 Jan 2018 17:50
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from:
Martin Wynne
West Of The Severn, United Kingdom



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p.s. John,

I think the turnout will need a curviform V-crossing.

Martin.

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6th message | this message only posted: 29 Jan 2018 11:38
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johndon
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Thanks again Martin, I managed to get the plan finished.  Out of curiosity, how would you know that the turnout would require a curviform V?  Is there some sort of standard of does it just come from experience?

John



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7th message | this message only posted: 29 Jan 2018 14:12
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from:
Martin Wynne
West Of The Severn, United Kingdom



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johndon wrote: Out of curiosity, how would you know that the turnout would require a curviform V?Hi John,

There is no specific rule, the track designer is assumed to know what he/she is doing.

As it happens this question has crossed with what I'm currently doing in the Templot Companion to replace the explanation in the old 2000 track planning tutorial.

Prototype curviform V-crossings are not used where not actually needed, because they involve messing about with the spacing of the crossing chairs and timbering. See:



The general guidelines are:

1. where the diverging track is part of a crossover, or leads to a loop or lay-by siding or other track running generally parallel to or alongside the main road -- always* use a regular (or generic) V-crossing. If there is no connected pointwork you may prefer to use a parallel type V-crossing instead.

2. where the diverging track needs to curve away from the main road, for example in a double-junction or in yards -- then you should consider the main road curving:

   2a.  if there is contraflexure (negative curving radius) you will almost always* want
          to use a curviform V-crossing. Otherwise you will get an unsightly reverse curve
          in the vee splice rail between the crossing and the TVJP vee joint position.
          I see this often in posted screenshots on other forums where the default regular
          V-crossings have been used for everything.

          But NOT if 1. above applies.
          This is why Templot can't make the change automatically.

   2b.  if the turnout is straight or curved with similar flexure (positive curving radius)
          any type of V-crossing can be used, but you will still often want to use curviform
          if you need the tracks to diverge rapidly.

3. where a regular V-crossing is used you can usually change to a generic V-crossing instead if you are modelling in P4, S7, etc., and prefer. But not if the combination of switch and crossing sizes would cause the turnout radius to exceed the switch radius, e.g. A not more than A-7,  B not more than B-8,  C not more than C-10, etc. (for standard-gauge, broad-gauge and narrow-gauge are different). For such longer sizes always use regular V-crossings.

Generally generic crossings are more difficult to build in model form because the turnout curve runs through the knuckle up to the fine-point. Especially when using wider than scale flangeways (00, EM, etc.). Which is why Templot defaults to regular V-crossings. Also the regular V-crossings shorten the turnout a bit, which is usually helpful in models.

*always means always except when it doesn't. :)

p.s. the track plan looks good.

regards,

Martin.

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8th message | this message only posted: 29 Jan 2018 16:49
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from:
madscientist
 

 

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excellent summary 
we're gradually sucking all the useful bits out of Martins head !! :D
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9th message | this message only posted: 29 Jan 2018 17:47
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from:
johndon
United Kingdom

 

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Thanks for the explanation Martin, much appreciated.

John
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