OO Gauge double track centres

[TravisM]

I've restarted modelling in OO gauge and I was wondering what the distance is between double track centres for both straights and curves so I can get a realistic looking double track mainline.  Obviously I'm looking for the distance in model form rather than 1:1 scale     

[Joseph_Pestell]

I usually get into trouble for getting this wrong!

 

The "correct" centre-to-centre distance is 45mm. The problem is that if you have curves of less than about 4' radius this will not be enough to stop 64' coaches (e.g. BR Mk1) from hitting each other.

 

So, for instance, Peco Streamline gives a 50mm centring which should allow you curves (preferably hidden) down to about 2' radius. Longer coaches such as BR Mk3 may give you a problem at 2' radius.

[Philou]

Here you go - in raising the point regarding my own layout proposal, 'gordon s' of this parish kindly did a run for me on templot and found that at 45mm centres you cannot run coaching stock side by side on a radius of less than 7 feet. I'm using 1.0m as a minimum so I will need to check the spacing on curves before any final pinning down. It may well be that it will be 50mm - we'll see.

 

Cheers,

 

Philip

[imt]

I usually get into trouble for getting this wrong!

 

The "correct" centre-to-centre distance is 45mm. The problem is that if you have curves of less than about 4' radius this will not be enough to stop 64' coaches (e.g. BR Mk1) from hitting each other.

 

So, for instance, Peco Streamline gives a 50mm centring which should allow you curves (preferably hidden) down to about 2' radius. Longer coaches such as BR Mk3 may give you a problem at 2' radius.

 

It's 6 ft between tracks, and 11ft centre to centre in 12" to foot scale.  But of course that's just theory.  There are a thousand and one reasons why 44mm will be too small centre to centre, some of which Mr. Pestell has noted. You will never get 12" to foot fingers in between lines in a fiddle yard unless its 55mm or more for example - mine are 65mm apart to get LocoLifts in easily!

[Pete the Elaner]

I agree: 45 is about correct.

I went through this a while ago & here are my calculations:

 

What we have:
Distance between centres = 16.5mm/2 (half track width) * 2 (because there are 2 tracks) + 2mm (approximate width of 2 running rails) + 32mm (streamline’s 6’ way) = 50.5mm

What I want:
Distance between centres = 4’ 8.5” I’m going to pause here because I can see Imperial is going to be a handful when I need to divide by 76 so I’m going to work in metric. This is 1422mm, which is much easier! I will assume that rail width is roughly accurate.. It looks about 3” (76mm) & for this purpose, it is good enough for me. 6’ is 1829.

Distance between centres = 1422/2 *2 + 76*2 +1829

= 1422 +152 +1829 = 3403

& convert that back to 4mm 3403/76 = 44.8mm

So Peco’s width is 50.5mm & my calculations show that 44.8mm is correct.

 

As mentioned, this spacing will cause problems on curves, so it is quite understandable for Peco's standard to be wider.

If all your curves apart from very gentle ones are off-scene (like mine), then you can widen the spacing away from the scenic section.

[TravisM]

I take it that double track centres on straight track is 50.5 mm?  I was told years ago to get a easy separation on curves was to lay your minimum radius curve first, then tape a pencil your longest vehicle you want to run round that curve, so the pencil is furthest from the inside rail.  When you have made that mark, lay the outer radius track and do the same but the pencil on the opposite side you used before and hopefully if it's done right, the pencil should trace over the original pencil line and get a realistic separation.  I hope that makes sense?

[NittenDormer]

If you want to include a double track crossover, Peco streamline work to a 50mm centre to centre gap, while setrack/Hornby use 67mm. You can get a peco track spacer for about 50p that does both. The larger radius setrack curves (radius 4 to [a theoretical] radius 5), the gap is somewhere in between, around 60mm. What you need depends on what stock (particularly, how long) you are going to run.

[DCB]

The Peco Streamline 50mm separation is a good working figure for most layouts,  The critical factors are locos with long overhangs, running on the inner track of a double track curve while long coaches, run on the outer.  Forget pencils or Templot, it is whether they hit which matters, and the widest part of the coach is higher than the extreme corner of the loco which is at buffer beam level

The worst case scenario mixes old 4-4-0s Triang L1s and M7s (running backwards) or the old tender drive Hornby King with Mk3 coaches, but I find 50mm Ok down to 3rd radius as I don't run coaches longer than Mk1s with long overhang locos.  The set track spacing gives more than enough clearance for worst case scenario on 1st radius and a tolerance for misalignment and I would only use it for curves bringing the gap down to 50mm or less on the straights.  

 

As has been said previously the 50mm is the spacing between the tracks of double track. The gap to loops sidings etc or between pairs of double tracks is generally noticeably wider, I believe the LNWR main line had evenly spaced lines as do many modern full size track layouts but I made the mistake of laying 4 evenly spaced tracks through our junction station and it now annoys me and I wish I had brought the middle pair closer.

 

Generally I feel the smaller the separation the better.  OO scale is after all 4mm scale stock on H0 gauge track so the 44mm spacing for 4mm scale comes down to nearer 40mm for 3.5mm.

I have pulled the clearance down as small as practically possible in the 40 to 42mm range to squeeze in as many sorting and storage sidings as possible  (see pic) the critical dimension being an ability for 2 Triang Halls to pass each other on the straight without clashing. 

 

If you lay at 50mm or closer centres you need to be very precise with track laying I would always lay set track curves on radii under 2ft even if I have to cut the sleeper webs and curve it to a sharper or easier radius as it keeps to shape and does not try to straighten out like flexi. 

 

If you must use set track spacing a few bits of junk between tracks like bridge girders and signal posts helps give a "reason" for the wide spacing.

[SRman]

I use the spacing dictated on straight sections by the Peco points distance on crossovers, but widen this out considerably for curves - my outer curves are to approximately 2' radius. I use the Bachmann class 166 coaches to test the clearances, as they are not only among the longest coaches in my collection (mark 3 coaches are also the same length), but they are wider than standard because of the more generous clearances on the Great Western main lines.

In the fiddle yard, I have widened clearances on the straight sections slightly to allow easier insertion of fingers to pick up or put down items of rolling stock.

[Harlequin]

Just to be precise: Peco Streamline point geometry is based on Imperial units - 2 inches between parallel tracks, which is 2 * 25.4mm = 50.8mm.

[Pete the Elaner]

For additional tracks, the spacing of the next rail of the adjacent is ten feet, but if it also is part of a double track main, then the spacing to its twin is six feet again.

 

I have heard this before but it does not always apply, certainly not on the London-Roade section of the WCML, where all 4 tracks are spaced evenly.

My guess is that this was laid before the rule was introduced, so the distances were maintained when the track was re-laid/re-aligned.

[royaloak]

Just because the area between 2 running lines is called the 6ft doesn't mean it is actually 6ft, just as the area between 2 pairs of tracks is called the 10ft even though it can be the same size as the 6ft, the numbers chosen mean there cannot be any confusion about which area is being talked about when the signaller and driver are conversing.

 

I can think of several places where the 6ft is much less than 6ft and also quite a few areas where the 6ft is much more than 6ft.

[royaloak]

I have heard this before but it does not always apply, certainly not on the London-Roade section of the WCML, where all 4 tracks are spaced evenly.

My guess is that this was laid before the rule was introduced, so the distances were maintained when the track was re-laid/re-aligned.

I don't think there is actually a rule just an understanding of which area is being talked about. Edited March 1, 2018 by royaloak

[Dunsignalling]

For double track on the mainline the spacing between the rails of the two tracks is 6 feet, on the straight.  It is increased on curves, but I don't have a formula, if there is one.

 

For additional tracks, the spacing of the next rail of the adjacent is ten feet, but if it also is part of a double track main, then the spacing to its twin is six feet again.

 

For carriage sidings, spacing is 8 feet.

 

All this for straight track, rule violations are known to exist.

 

John

The prototypical six-foot and ten-foot spacings are nominal measurements and should generally be regarded as a minimum rather than a standard.

 

Where the "six-foot" is significantly less than 72", there will be operational restrictions imposed to avoid problems, e.g. certain stock being prohibited.

 

John

Edited March 1, 2018 by Dunsignalling

[Zomboid]

You get all kinds of combinations of nominal 6 & 10 foots. 6-10-6 and 10-6-10 are the most common as far as I can tell, but some bits of the GWML are (so I've heard) 10-10-6 where the fast lines are at broad gauge spacing and the slow lines are at standard spacing. And between Clapham and Waterloo there are 8 tracks all at "6 foot" spacing.

You can pretty much do what you like if you're not modelling a specific location.

[martin_wynne]

I agree: 45 is about correct. I went through this a while ago & here are my calculations:

 

Hi Pete,

 

The correct answer is 44.67mm, except on GWR and BR(W) where it is 44.83mm

 

It is always much easier to work in prototype dimensions, in inches.

 

Track gauge 56.5"

2 rails 2.75" wide = 5.5"

6ft between them = 72" (minimum)

 

Total 134" (11ft-2in). Divide by 3 to convert prototype inches to model mm at 4mm/ft. So 134 divided by 3 = 44.67mm minimum centres.

 

On GWR and BR(W) it is half an inch wider:

 

Track gauge 56.5"

6ft-6in between rail running edges  = 78" (minimum)

 

Total 134.5" (11ft-2.5in). 134.5 divided by 3 = 44.83mm minimum centres on GWR.

 

But you need wider spacing for a running clearance on model curves. Templot includes a "dummy vehicle" tool to generate the clearance envelope for any radius and size of rolling stock:

 

 

Yellow shows the physical space occupied by a bogie vehicle traversing the curve. Blue shows the suggested clearance space each side. All these things are adjustable to suit your rolling stock.

 

regards,

 

Martin.

[Compound2632]

There's absolutely no reason why you can't use the scale 11'2" (say 45 mm) between centres on the straight. It's just that you have to widen that on curves, with a suitable transition geometry and some way of hiding the fudge, such as a bridge with a centre pier. Also, if using Peco points, this forces you to discard the unrealistic diagonal sleepers when building a cross-over. Cross-overs are also shorter and an added bonus is that bridges etc. can be to scale dimensions.

[kevinlms]

I have heard this before but it does not always apply, certainly not on the London-Roade section of the WCML, where all 4 tracks are spaced evenly.

My guess is that this was laid before the rule was introduced, so the distances were maintained when the track was re-laid/re-aligned.

Correct, that's what happens when you are a pioneer in something. You make the mistake and others benefit from it. I believe that trackwork on the WCML still presents problems with access to track renewals etc.

[DCB]

Just back from Frampton Mansell a level crossing on a section of reverse curves on the ex GWR Swindon - Gloucester line originally broad gauge where I measured the 6ft way spacing between the outside faces of the rails and it actually was at 6ft as near as I could measure with a tape measure, that is with the benefit  of the right angles of the rubber blocks of the crossing to guide me.   I was expecting rather more, and the lack of obvious super elevation was a bit of a surprise, perhaps due to the gradient which I believe is 1 in 70 at this point and the lack of room for gentle transitions from left to right cant. .   

 

I know people usually talk about track centres rather than spacing between tracks but that 6ft is 24mm in 00 or 21mm in H0 add in the track gauge and the width of rail heads and H0 track spacing is coming out at 39.5mm and EM at 42mm. However when I took a ruler to some of my tracks the issue was some stock is wider than scale, Old Triang derived Hornby is especially bad but some of my straight track is 42mm or less and I haven’t had any significant problems.

 

 

 

[martin_wynne]

I know people usually talk about track centres rather than spacing between tracks but that 6ft is 24mm in 00 or 21mm in H0 add in the track gauge and the width of rail heads and H0 track spacing is coming out at 39.5mm and EM at 42mm.

 

That method won't work for 00 and EM. The track gauge may be narrower than scale, but the rolling stock isn't. This means the track centres need to be the same as the scaled prototype dimension, not the distance between the rails. As I posted before, the correct prototype dimension is 11ft-2in centres or (11ft-2.5in centres on GWR tracks), minimum. That makes 44.67mm (or 44.83mm) minimum centres on the model. If you make them less than that as you suggest, you will not have the proper clearance between vehicles.

 

Martin.

[Enterprisingwestern]

In some other threads we've had  "something blindingly obvious to me but not necessarily others" moments, so if I may mention that track centres are easier to measure and draw out from rail to rail, the same left or right rail of each track, obviously!

 

Mike.

[Pete the Elaner]

That method won't work for 00 and EM. The track gauge may be narrower than scale, but the rolling stock isn't. This means the track centres need to be the same as the scaled prototype dimension, not the distance between the rails. As I posted before, the correct prototype dimension is 11ft-2in centres or (11ft-2.5in centres on GWR tracks), minimum. That makes 44.67mm (or 44.83mm) minimum centres on the model. If you make them less than that as you suggest, you will not have the proper clearance between vehicles.

 

Martin.

I agree. This is why the 6' will always look too wide in 00 gauge if you reduce the distance between centres to something closer to scale.

[DCB]

In some other threads we've had  "something blindingly obvious to me but not necessarily others" moments, so if I may mention that track centres are easier to measure and draw out from rail to rail, the same left or right rail of each track, obviously!

 

Mike.

When you lay track it is much easier to measure the distance between rails than the centres, Sorry but it is so blindingly obvious that it shouldn't need mentioning, I use a gauge which is actually a ruler.  This reliance on drawing leads to poor tolerance on track alignment so many of you talking about 42mm being too tight actually lay track to plus or minus 1mm which is 40-44mm on a nominal 42mm, especially where track is stuck down and ballasted.

 

See pics.  35mm is Liverpool and Manchester spacing in H0 I believe! (Ok for Hornby 0-4-0Ts)

42 / 42,5 looks good

38 OK for inside cyl locos, but not 28XX

Edited March 12, 2018 by DavidCBroad

[Enterprisingwestern]

When you lay track it is much easier to measure the distance between rails than the centres, Sorry but it is so blindingly obvious that it shouldn't need mentioning, I use a gauge which is actually a ruler.  This reliance on drawing leads to poor tolerance on track alignment so many of you talking about 42mm being too tight actually lay track to plus or minus 1mm which is 40-44mm on a nominal 42mm, especially where track is stuck down and ballasted.

 

I'm glad you used the term shouldn't. I've had the "enlightening" conversation more than once at exhibitions, especially to new tracklayers. What is blindingly obvious to some may not be to others.

 

Mike.

[martin_wynne]

When you lay track it is much easier to measure the distance between rails than the centres, Sorry but it is so blindingly obvious that it shouldn't need mentioning, I use a gauge which is actually a ruler.  This reliance on drawing leads to poor tolerance on track alignment so many of you talking about 42mm being too tight actually lay track to plus or minus 1mm which is 40-44mm on a nominal 42mm, especially where track is stuck down and ballasted.

 

In 4mm/ft scale (00, EM or P4) the centre-to-centre distance for UK standard-gauge models should be not less than 44.67mm, and wider on sharp curves. For 00 and EM that is commonly rounded to 45mm.

 

To measure centre-to-centre, measure from the edge of the left-hand rail on one track to the same edge on the left-hand rail on the other track.

 

Posting misinformation about using narrower spacings is not fair to beginners. If you want to do it that way on your own railway, fine.

 

Martin.