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Overlapping Turntable Entry


Lacathedrale
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Good morning chaps,

 

I've come across a rather fascinating plan which involves a turntable runaround. Here are two views from the platforms:

 

image.png.2e03c5a378db516955e71a5126195005.png

 

image.png.44ba596b3926bfdfef7db32b9dcffeff.png

 

 

and here is one from the bufferstops:

 

image.png.0e86e70cbd8321c5543485681e69f987.png

 

The railway company plan is as so:

 

image.png.bc2b234c797707fb20bc3f762046fe8c.png

 

This was my attempt in templot:

 

image.png.08847cabccdca4436512c959d0694e0a.png

 

My method was to create two diamond crossings, omitting the relevant stock rail and check rail. It seems like it might be a bit hairy having perfectly opposing crossing noses, but clearly it works as per the prototype? It also seems particularly ridicolous that the tip of the two diagonal roads meet in a single vee.  My gut feeling is that this will infact be the most challenging part of the  formation - a big wide strip of copper clad under the convergence of those four rails would most definitely be required. I think the whole 'W' shaped assembly of the crossing vees and resultant stock rails in the middle of the diagram could be powered via a frog juicer.

 

Any thoughts?

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 The close up photos and part plan - is this Ramsgate Harbour (LC&DR) station in the 1880S ?  Just curious, as the station had an unusually cramped track layout.

Regards,

SIGTECH,

Steve.

Edited by sigtech
grammar
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What a lovely subject for a model, and doubtless some fine Victorian trains as well.

 

You'll need to insulate between the two crossings to use the middle road, so I imagine you will make the turntable edge V separately (which, I see, is what the builders of the prototype did).

 

Are your angles right in the Templot drawing? They are certainly bigger than the coloured plan, and it looks like you'd only manage a very short turntable. The centrelines of the three tracks should all meet at the centre of the turntable, and the turntable diameter is twice the distance from the turntable edge V to the midpoint of a line between the two crossing Vees each of the crossing Vees.

Edited by Jeremy C
Incorrect information now corrected
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12 hours ago, Lacathedrale said:

It also seems particularly ridicolous that the tip of the two diagonal roads meet in a single vee.  My gut feeling is that this will in fact be the most challenging part of the  formation

 

 

Hi William,

 

It's not a conventional vee. The nose will be blunted back to a full rail-width.

 

cheers,

 

Martin.

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Please ignore my earlier comment regarding Ramsgate Harbour station, William - I realize now after reading the layout planning section of RMWEB that we are talking about Bromley North...Interesting track layout..

Regards,

SIGTECH

Steve.

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I've barely used Templot, and certainly not for anything like this, but the essential thing is that the centrelines of all three tracks meet at the centre of the turntable. If you want all three tracks to be straight till beyond the crossings, and you want both crossing angles to be the same, then the crossings have to be in line (or the same distance from the turntable pit might be a better way of expressing it).

 

It is easy* to calculate what the crossing angles should be from the turntable diameter. As an angle, it is

θ = sin-1 G/D

where G is the gauge and D is the turntable diameter, both in the same units. 

 

In 1 in x format, x is close to 1 in D/G. If you need an accurate value, then

x = 1 / 2tan θ/2

at least, this is what real railways use, but I recall reading that Templot uses the tangent of the crossing angle rather than the tangent of the half-angle, which is a rather simpler

x = 1 / tan θ

although at this sort of angle there is hardly any difference between the two.

 

*At least, it ought to be easy, but this didn't stop me making a mistake in my earlier post, now corrected, and I would welcome this post being checked by someone whose brain hasn't gone to mulch.

Edited by Jeremy C
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Good grief, Templot does all that for you. :)  You omitted to allow for the gauge intersection being inside the turntable perimeter -- the middle vee is blunted back to a rail-width at the turntable edge.

 

Here is a scruffy bit of video showing how to do it in Templot. The tracks are rotated until the rail-width is central over the centre-line at the perimeter. For EM gauge and a 50ft turntable, the crossing angle turns out to be 1:10.4 RAM each way.

 

The turntable ring is a dummy centre-line-only track template, curved to 25ft/100mm radius.  Here's the video:

 

 https://flashbackconnect.com/Default.aspx?id=KqdtokYRmEvmFe9nTo5o-g2

 

cheers,

 

Martin.

Edited by martin_wynne
typo
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26 minutes ago, martin_wynne said:

Good grief, Templot does all that for you.

As I said, I have barely used Templot. I am impressed!

 

I realised after I posted that the effect of the truncated vee was not negligable, and that the turntable diameter would therefore be larger than my D value.

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