Author Topic: Double track spacing  (Read 589 times)

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Offline MikeWilliams

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Double track spacing
« on: August 11, 2017, 09:48:32 AM »
I thought this had been discussed before, but I can't find it.  So, as I am about to commit myself (not before time some would say!) to laying track I would value feedback from others please on the spacing of double track.

Prototype minimum is 6ft (81mm) but that is often widened.
A well known G3 garden track uses 7in (177mm).
The G3S track standards don't give a measurement.
The G3S M01 modules gives various dimensions which I calculate to be 115mm.

So, with out of scale curves (I'm using R15ft) giving more throw out, lots of slop between wheels and rail, and possibly the occasional slightly out of scale vehicle, what do people use and have you experienced any problems at all?

Thanks,

Mike

Offline cabbage

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Re: Double track spacing
« Reply #1 on: August 11, 2017, 12:02:01 PM »
I use a rail to rail distance of 165mm the curves on the double track corner are 3.5 and 3.3m radius .

I only have wagons on the track at the moment but LMS 57' coaches soon. So far the only problems have been gages, figs and grapes on the line...

Regards

Ralph

Offline AshleyW

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Re: Double track spacing
« Reply #2 on: August 11, 2017, 12:16:48 PM »
i think grahams double track is 160mm and is 17.5 foot rad, not had any coaches touching when on both lines.

Offline Peaky 556

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Re: Double track spacing
« Reply #3 on: August 11, 2017, 10:34:09 PM »
Mike, I have penned this draft for the forthcoming G3 site that John Candy is masterminding.  I hope John takes no umbrage for me giving a snapshot view!
Regards, Tim
Double Track Spacing
Our full-size railway in the UK has traditionally referred to the gap between adjacent tracks of a twin or multiple track section, as the “six foot”. We shouldn’t take this too literally however, but as a starting point it suggests the spacing between tracks centres is about 11 feet. In our scale this translates into around 151 mm. With typical stock no wider than 9 feet, this leaves a clear 2 feet between passing trains. There are several and varied reasons why we don’t use anything this small on a G3 set-up.
Firstly, the rolling stock width permitted by the G3S is 140 mm, which equates to nearly 10 ½ feet lifesize. This overly-generous width is to allow for continental, but not quite US stock which is slightly over 10 ½ feet (128”).
Secondly our curves are much tighter than the average of our big brother. Bogie stock is caused to both project outwards on the outside of the curve, and underhang as a chord across the inside. Two such vehicles meeting on adjacent tracks of 151 mm centres, on any practical garden-sized curve, will have a dramatic coming together! I would hate to see this happen.
Thirdly, and relatively trivial compared with the above two, is the need for the ‘big hand in the sky’ to perform rescue operations in case of derailment. In a confined multi-track set-up there wouldn’t be much room for fingers.
The net result of all this is that the G3S standardise their portable track modules with 185 mm centres which can be downloaded here. This has been calculated to cope with the great majority of stock running down to fairly tight radius curves. As such it is a compromise, and so suitability should always be checked out, slowly and carefully by hand, if you bring your own stock to a strange railway!
Now we are not bound by any G3S police to use 185 centres; in fact we can use any centre spacing we like, as long as our own stock, and that of friends and GTG invitees, will circulate safely. On my track I am playing tunes with the spacing, which will be down to 170 mm in many places. In theory this gives a spacing of at least 30 mm between vehicles, but only on the straights, less on curves.
Why do I bother deviating from the standard? Well I am confined for width in some places, such as in a cutting, over a bridge, and along some pre-cast concrete track bed sections. These are all either straight or very nearly so, and so the overhang should not become a problem. If it does I shall be editing this article with dire warnings!

Offline MikeWilliams

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Re: Double track spacing
« Reply #4 on: August 12, 2017, 08:19:43 AM »
Thanks Tim,

You mentioned "six foot" but then "centre to centre".  Depending on what rail you are using, I calculate that the G3S 185mm equates to 116mm between tracks and your 170mm to about 102mm.

Another member with a very large track has written to say he used 110mm and that an old G3S Newsletter had an article about calculating what to use.

I am now not 100% certain which measurement others have quoted, but so far as I am aware the prototype is always measured between rails (6 foot)?

That being the case I'll probably go for 110mm on curves but tighten to 100 or even a tad less on straights as it will look so much better.  I'll now go ahead and make the remaining baseboards, but that's a good starting point.
 
Thanks all.

Mike

Offline cabbage

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Re: Double track spacing
« Reply #5 on: August 12, 2017, 01:31:32 PM »
According to HG the rail to rail spacing should be 111mm. Being lazy I have always used rail to rail!

Regards

Ralph

Offline Peaky 556

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Re: Double track spacing
« Reply #6 on: August 12, 2017, 10:32:04 PM »
Mike
Being an engineer I try to use unambiguous terms, so although I mention the traditional "six-foot" between tracks, it is not a term I like.  I then talk only in terms of track centres, because that is exactly defined whereas 'between rail' spacing could mean several things and there is dependency on rail thickness.  Call me pedantic if you like.  To help get it right I have made up some templates in ply to skim along the rails and check for consistent centres, viz:



what is image hosting

Offline IanT

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Re: Double track spacing
« Reply #7 on: August 12, 2017, 11:00:23 PM »
Hallo Mike,

The first written guidance in this area (that I am aware of) was by Alan Marsden in NL49 - June 2002. This followed questions at the 2001 AGM on the subject. Alan recommended a "between track centres" dimension of 6.5" to 7" giving 4" to 4.5" between adjacent rails. This was based on empirical calulations based on the overhangs from G3 BR Mk1 Coaches (full sized ones being 67ft between buffers) on a 15 foot radius curve. This article was repeated in NL82 (Sept 2010) following questions on the Forum.

The G3 M01 Module standard used a track spacing calculated using the MOROP 'Norm' - NEM 103 "Track Clearance for Curved Track" (the 2004 version, which has since been updated). For simplicity , it was assumed that the 'bogie-vehicle' in question was Alan's BR Mk1 Coach. The use of NEM 103/112 followed the general M01 design approach of using Spur II and European standards where possible. I thought the details were published in the NL but I cannot find them if they were. I'm sure there has been discussion on this topic on the Forum before though.

The "6 foot way" was measured from the outside edge of the adjacent rails but this distance was increased on curves by varying amounts. So in G3 a 'scale' six foot way would be 81mm (80.92 to be exact) mm or 148.5 mm (63.5 + 4 + 81) between track centres (assumes 2mm across each rail head). The M01 standard uses the 185mm track centre measurement calculated as per NEM 103 mentioned earlier and it was simpler to use the same spacing on straight & curved sections.

On the portable track sections I'm building currently, the 'base' of the sections is 150mm wide - so two track  sections placed side-by-side would in fact only be slightly (1.5mm) over a scale 6ft way. But as stated this distance was widened in full-sized practice on curves and I will use the 185mm spacing for curves should I need to do so.

People can of course use whatever measurement they wish to.

Regards,

IanT
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Offline Peaky 556

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Re: Double track spacing
« Reply #8 on: August 13, 2017, 08:45:38 AM »
The information in Alan's article in NL49 should be perpetuated and recorded in a more accessible manner to all G3 folk.  So to the open question.  How could the file be made available? Is there an electronic archive somewhere, to which all NL editors add?
Tim

Offline IanT

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Re: Double track spacing
« Reply #9 on: August 13, 2017, 09:09:38 AM »
Only those articles which have been recovered and added to the G3S website Tim.

I will see if I can re-type Alan's article (and scan the diagrams) and place it in the same area as a downloadable PDF.

Regards,

IanT
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Offline IanT

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Re: Double track spacing
« Reply #10 on: August 15, 2017, 09:50:49 AM »
I've now re-typed Alan's original article but have still to scan the associated diagrams. I will try to get this done today and the PDF posted in the next day or so.

I've also been looking back through my files to try to recall some of the background to the M01 standard, which is probably academic now but may still be of interest. I must admit, I had forgotten some of the 'evolution' detail. The first M01 version (29/03/2010) recommended that any second straight track centre should be 385mm from the modules edge - giving 160mm between centres. The 'way' was therefore 92.5mm - which scaled at just under 7ft - within prototypical size (which varied between 6 - 7ft).

An unpublished standard - 'M02 Track Clearance' (01/10/2010) was based on the NEM 103 previously mentioned and included the following guidance:

C3 Track Clearance

On straight twin track modules, the centre-line of the second track connector is defined in M01, as being 385 mm from the front edge of the module. This provides 160mm between the two track centres. On a single track the clearance should therefore extend to 80mm on either side of the track centre. 
 
It is recommended in M01 that certain curve radii be adopted in practical use, the radius being measured to the centre line of the track (or outer track if twin tracks are used). These curves are at 1500mm, 3000mm, 4500mm, 6000mm & 7500mm radii, the 1500mm curve only normally being used where space is limited.   Within this range of track radii, the track clearance should be extended by the dimension ’E’ which is a  function of the curve radius and the vehicles that will be used. This guideline assumes a maximum vehicle length of 79ft 6” (1,072mm at 13,5mm/ft) and a maximum between-bogie pivot distance of 56ft 6” (762mm).
 
On curved twin track modules, the distance between track centres can be defined as (160+2E) mm.

Outer Track Radius       E                160+2E
1500mm                     49mm          258mm
3000mm                     24mm          208mm   
4500mm                     16mm          192mm
6000mm                     12mm          184mm
7500mm                     10mm          180mm
 
Clearance should also be widened at a point beginning not less that 650mm from the beginning of the curve. Within this transition area the clearance should increase from 160mm to the new value in a linear fashion.


A diagram from NEM 103 was included.

However, it was felt that this was far too complicated in practice and so a compromise was reached, where the second track centre distance was increased to 410mm (giving 185mm centre distance - e.g. about 6000mm radius curves) and no transition from straight to curved clearances would then be required. The M01 was re-written to reflect this, the last published version being dated 07/02/2011.

So the "G3 Police" went to some considerable trouble to guide members in this area but most have chosen to go their own way, as they are perfectly free to do so.

Anyway - whether this helps or not - that is some of the background to what has gone before...

Regards,

IanT   
 
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Offline IanT

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Re: Double track spacing
« Reply #11 on: August 15, 2017, 04:15:32 PM »
Alan's article has now been placed on the Gauge '3' Society website as a PDF document. It is available to anyone who would like it for download. No Member log-on is required.

Look under  - About Gauge 3/Articles and Reading/051 - Track and Lineside Clearances - Alan Marsden - June 2002.

...and click on the '051'

Regards,

IanT
Nothing's ever Easy - At least the first time around.

Offline Peaky 556

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Re: Double track spacing
« Reply #12 on: August 15, 2017, 07:07:17 PM »
Ian, re your unpublished stuff from earlier today, truly excellent stuff Ian.  This is exactly what the outdoor constructor needs, rather than the module maker where compatibility with others' modules will be required.  I for one will now be happy to go down to 160 centres on straights, with a transition to widening as curves approach.
A couple of comments and a query:
·       The vehicle length used is very long, presumably something like a modern mainline coach, so early BR diesels of around 67' or BR Mk1 coaches will have no problems.
·       Vehicle width used was probably the G3S standard of up to 140 mm.
·       Would I be treading on anyone's toes if this data was distilled into an improved article on track spacing in JC's G3 site? (I am assuming that Alan Marsden's NL49 article is effectively copyrighted by G3S and should remain as-is on their website).  I've not had time to look at it yet.
Regards, Tim

Offline IanT

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Re: Double track spacing
« Reply #13 on: August 15, 2017, 07:59:44 PM »
Hallo Tim,

I'm afraid I can no longer remember the detail of where the bogie vehicle dimension came from but I think we probably decided on a 'max' sized prototype to be on the safe side.

Although M02 was written for 'Modular' use - the guidance given would of course work perfectly well on any garden railway, provided the suggested 'transition' is used.

The original NL article is essentially the joint copyright of Alan Marsden and the Society but I would very much doubt if either would claim the guidance as being 'proprietary'. So I can see no issues with you using the same guidance/information in your own documents - in fact I think it is preferable for any guidance in this area (from whatever source) to be broadly compatible.

Nor do I have any objections to the information I have provided from the draft M02 being used. I will be very pleased if it is useful to people.

Regards,

IanT
Nothing's ever Easy - At least the first time around.

Offline MikeWilliams

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Re: Double track spacing
« Reply #14 on: August 15, 2017, 08:05:59 PM »
So the "G3 Police" went to some considerable trouble to guide members in this area but most have chosen to go their own way, as they are perfectly free to do so.

That may well be the case Ian, but thanks to you, Alan et al they made an informed decision to do so, rather than a stab in the dark!

Mike