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                 Curved track work and turnouts within curved track
     
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1st message | this message only posted: 14 Jun 2020 07:24
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from:
Graham Long
 

 

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HiI am trying to get my head around some concepts related to curved track and turnouts within curved track.
1. I am designing a branchline terminus. I am not sure if I need to worry about transition curves. Are transitions only used where running speeds are much higher?
2. Does all curved track on lines running need cant regardless of it being either fixed radius or transition?
3. I read that turnout's arn't prototypical in the transition curve. Does this mean that all turnouts must be totally outside the area of transtion?

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2nd message | this message only posted: 14 Jun 2020 11:22
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from:
Martin Wynne
West Of The Severn, United Kingdom



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Hi Graham,

Are you asking about prototype or model?

On the prototype, full mathematical transition curves are used only on fast main lines. They would always be provided with cant, the transition providing a length in which to ramp up the cant and then ramp back down to level track.

For branch lines, it would be more normal to use lengths of varying fixed radius than a full mathematical transition. Even on branch lines, some cant would normally be provided for sharp curves, otherwise a sharp curve on the flat needs a significant speed restriction.

Often in yards and on branch lines you might find a "platelayer's transition", which means the gang have eyed-in a smooth curve without it being a proper mathematical transition.

On a model we can do exactly the same as above. But often on a model we need to use much sharper curves than the prototype, and sudden changes of radius are more noticeable. A transition curve is then a good way to disguise the severity of the curve and improve the running qualities, even on the flat and in situations where the prototype would use fixed radius curves.

Also in Templot, transition curves are used as a means of linking a smooth curve between existing templates, using the make transition function.

More about all this here:

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

Turnouts are not usually installed in a transition zone because of the rising/falling cant gradient. That introduces a twist in the track which makes it all but impossible to install workable switch blades. But they can be installed where there is a fixed amount of cant, using two-level chairs. For example where a branch line makes a junction with a fast canted main line. In such cases there would be a severe speed restriction over the branch divergence, because of the adverse cant.

In Templot you can insert a turnout in a transition zone if you wish, again for purely model reasons of lack of space. If you do that I would recommend building it flat, rather than canted. Templot is a 2-D program referenced to the rail top, and has no functions related to cant or gradients. That remains for the modeller to arrange or not as he wishes. 

cheers,

Martin.

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3rd message | this message only posted: 17 Jun 2020 07:46
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from:
Graham Long
 

 

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Thanks Martin
I will absorb this information as well as I can and see if I have any further queries
Regards Graham
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