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1st message | this message only posted: 11 Dec 2018 10:00
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from:
Andrew Smith
 

 

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Dear all
I feel a bit of fraud posting here as I have struggled but failed to come to terms with templot for years. I require help in understanding some prototype track issues but the final plan may well end up being drawn with a bendy stick and fixed curves.

The Model -  Having used traditional methods to create a 2mm model of the mixed gauge (broad and standard) Vale of Neath Railway station at Neath I now want to capitalise on the 1:500 town plan to recreate Aberdare station at near scale scale size. N.B Luckily the track was cross-sleepered so less of a problem than baulk road and none of the standard gauge track changes sides through any of the turnouts. That takes a bit of pressure off . . . 

The problem - The layout is governed by four, 3 way turnouts. Of the 4 three are mixed gauge. The town plan includes all rail lines in both gauges (more on that later) but I am struggling to make sense of the geometry. Clearly the draughtsman used a common sense approach to laying out the sidings etc. but I having difficulty locating the vees and any associated angles or track radius. 

Three excerpts are attached. 
1. The station throat turnout highlights the fact that the mapmaker's attention had wavered as it includes an additional rail that goes nowhere. The detail on this turnout is a bit confusing in other areas too.
2. The next one along that governs entry to the goods yard appears to interlace a diverging BG only siding before the main vees of the 3 way (struggling to explain that clearly but hopefully the picture helps). Is that likely? Is it possible? In such an important location I would have thought the diverging rail would have been further down the line to avoid derailments but there isn't space to accommodate that.
3. The 3 way at the end of the goods roads seems very 'straight' to me. Is it possible that tracklayers would have accepted very straight connections here rather than normal curved stockrails? I am pretty sure that this could be replicated by using a 3 foot ruling radius on both sides. 

At this stage I only need/want to worry about the BG lines. The NG ones all pretty make look after themselves. 

I have looked through my BGS fact sheets on trackwork etc. but it largely focuses on baulk road. Pictures rarely show mixed gauge 3 ways and I certainly can't find anything that suggesting an interlaced diverging road.

Dropping below 3' radius also creates a few problems in construction as space becomes very limited in 2mm as crossing angles get shallower.

So after all of that rambling the real questions are:

(a) Is there likely to be a ruling crossing angle that all of these 3 ways will abide by? If so then obviously I can jig build but the plan suggests different radii on some lines. That may be down to the draughting rather than a reflection of reality??
(b) Is there likely to be a 'typical' candidate? 1:5/1:6 or what have you.
(c) Would that crossing angle be the same on the NG and the BG lines? I have built 2mm mixed gauge track using standard curves which means that transitions and vees also tend be curved. Luckily 2mm is quite forgiving.

Any help gratefully received.

Kind regards

Andrew



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Goodsentrance.png
 
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2nd message | this message only posted: 11 Dec 2018 10:35
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from:
Bernard Haste
 

 

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Has anyone ever considered just HOW accurate O.S. maps may be?

The cartographers may not have been railway savvy and a three way point or double slip may just have been a jumbled mass of metal.

Also, has anyone ever seen maps of the second world war vintage? Some maps show what might be described as abandoned railways - no tracks at all. This was done for security reasons although how this was going to work has always puzzled me.

Also it is known that, for copyright reasions not all the detail on maps is correct. This is so O.S. can prove it is their detailing if it is copied and published by a third party. Also certain, shall we say, `sensitive` information is not likely to be present, or is `misplaced` or is incoorectly represented. I think that the London Post Office Tower location is a secret so is not shown on OS maps (I have not checked this but was told it was the case whilst at college between 1974-6.

So I think relying on O.S. maps without corroborative evidence is likely to be misleading.

I`m also told that the track layout at Andermatt station in Switzerland is a state secret. This is for military reasons. As the whole station can be seen panoramically when on the ramp leading from Andermatt towards Disentis or from the public road, this does seemn to be a bit non-sensical.

Bernard
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3rd message | this message only posted: 13 Dec 2018 21:16
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from:
Andrew Smith
 

 

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Hi Bernard. Comparison of the mixed gauge trackwork on the 1878 town plan for Penzance with photographs suggests that the map makers were actually pretty accurate. On that basis I am prepared to accept that the Aberdare plan also reflects the actual running lines. The problem lies in the compromises on the part of the draughtsman in reproducing curves and consequent effect on crossings etc.
Andrew
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