Correct timber positioning at crossovers and junctions

[Phil G]

Hi Martin/Phil O
just a quick question if you don't mind re correct prototypical positioning of timbers.
In the attached screen shot, (which is from a box file posted today relating to a completely different question.)
I noticed the timbers have been laid out in such a way, that on the crossover road several are made up of timbers from the opposing turnouts, resulting in the timbers terminating in the 4' but with one chair on one timber and the opposing chair on the other timber. I believe timbers x-3x x-6c and X-9 are designed to represent three long timbers spanning the full crossover.
My question, is that prototypical to have what is basically a join in the middle of the 4'? I can see how this would save on needing longer timbers, but does it not increase the chance of the rails spreading as there is a risk of independent timber movement between the two rails? or would the tie timbers at x-3x,x- and x6c and x-9 be enough to prevent rail spread.
Please note my question has nothing to do with the work in the photo. I am just using this as an example to better understand correct practice when it comes to the more complicated laying of timbers. Given its my understand long timbers are avoided where possible. this maybe a plausible case for smaller timbers.
I guess one possible answer is, you would not see this on a main running line, but it may sometimes be seen in sidings.
cheers
Phil

 

[Phil O]

Hi Phil,

I have seen timbers spliced, but not in a standard crossover. Spliced timbering use a fishplate to secure the two ends together, using chair screws.

In the situation that you have there, I would use equalised-incremental timbering, it will be a lot neater.

HTH.

 

[Martin Wynne]

@Phil G @Penrhos1920

Hi Phil,

I have written about this many times over the years. I will write a few notes again here.

1. prototype

There is no such thing as the "correct prototypical positioning" of timbers in a crossover, unless you are modelling one specific crossover from a photograph or a site layout drawing.

The REA designs were introduced in 1925 to provide a commonality of chair designs across the companies taking part, i.e. all except the GWR. The REA designs specified the size, position and spacing of the chairs on the rails.

The layout of the timbering under the chairs was left to the individual companies, because it needs to be based on the site layout, ground conditions, traffic loads and running speeds, and the price of kippers.

For use in sidings and yards, engine sheds, etc., short timbers or even plain sleepers can be used to minimize costs and re-use serviceable materials. There are some LNER drawings of such crossovers on pages 102/Y and 103/Y of the NERA reprint of the REA "Standard Railway Equipment" drawings -- "Short Timbering For Crossover Roads".

Such short timbering would not be used for running lines*, where long timbers are needed to create robust track and prevent gauge spread. Generally the number of long timbers would depend on the ruling curve in the running line, sharply curved track needing to be more robust with more long timbers. In models we often use curves much sharper than the prototype, which means that to look the part we need to use more long timbers than might have been the case on the prototype.

For crossovers in secondary lines, branch lines, goods loops, etc. there might be fewer long timbers, but there will be some.

Where short timbers are used they would be interlaced between each other rather than joined end-to-end. This is in order to use the standard stock lengths without needing to be cut to size on site, which would remove the pressure-creosoted end-grain, leading to more rapid timber rot.

Sometimes very long timbers are created by splicing shorter timbers end-to-end, using an old fishplate screwed across the splice, but this would be done by the gang on site, rather than specified in the site layout drawing. This is more likely where a timber longer than 19ft-6in or 20ft is needed and is not available, that being the standard stock size for long timbers spanning normal 6ft-way double track. Extra creosote would be sploshed into the splice, but not always very effectively. Sometimes such timbers might be linked end to end with a screwed-on fishplate, but without cutting an actual splice joint into the timbers. In that case it is not strictly necessary for the timbers to be perfectly aligned with each other.

*Except possibly for wartime (WW2) renewals because of shortage of materials.

2. model plug track

If you use timbers aligned end to end as in your screenshot, you will have problems with webs and timber flanges conflicting into the sockets. It will also be very tricky to get perfect timber alignment and preserve the correct chair positions.

The intention is that you don't do that. Extend the long timbers across to the full width from one template to the opposite one, and on the opposite template click the hide outline button. This will remove the unwanted timber but retain its chairs, which will then be captured by the extended long timber. If the captured chairs are the standard interchangeable chairs (S1, L1, CC, etc.) they can be shoved along to align them centrally on the extended timber. I have written this several times and demonstrated it in ZOOM meetings. There is a limit to how many times I can keep saying the same thing. Here again is a screenshot showing this:

Timber A1 has had its outline hidden, and its chairs are being shoved along over the extended timber from the template below. Timber A2 has already had that process done.

(A2 has also had its chair heaved to L1 to avoid a conflict.)

cheers,

Martin.

 

[Phil G]

@Martin Wynne @Phil O
Thanks guys for both your comments,
I guess my terminology could have been better, by using the word prototypical I should maybe have said "what would the real railways have done in the day"
Martin your detailed answer under the heading prototype is very helpful. thank you

As to your comments about the model plug track, I have also attended the zoom meeting on extending timbers. so I would have approached it exactly as you have written. In fact I may very well over use extended timbers. It was never my intension to highlight Penrhos1920 approach, only to use it as an example of a split timber example.
cheers
Phil,

 

[Stephen Freeman]

Almost totally nothing to do with the topic, but in France I have seen timbers overlapped (simple lap joint) and re-inforced with a couple of metal straps. The timbers in question were not in use on the railway at the time, so I can't give a date when in use but definitely quite some time ago and old railway sleepers.

 

[Martin Wynne]

.
Here is a photo from Alan@york, showing a crossover with a mix of long timbers, short timbers and interlaced timbers.

And also parallel-wing chairs:

See: https://85a.uk/templot/archive/topics/topic_3590.php#p28802

Thanks Alan.

 

[Phil O]

The critical part of S & C is to support the special chairs, especially at the crossing. The rest of the standard chairs including check chairs are fitted where they land on the timber, within the constraint of the number of chairs required to support the traffic running over it.

 

[Phil G]

Thanks Phil and Martin thats very helpful advice,
going forward I will assume for the sake of the full sized crossing, we are talking X, Y and where fitted Z chairs and A, B, C,D and where fitted E and F as being the special crossing chairs, vee angle dependant. That will need long timbers. With the all the P chairs being the special switch chairs.

Looking at all the photos which have been very helpful. It looks as though, if split timbers are used in the 4 foot, there are not many used concurrently, and a parallel wing rails will also help spread the load, and this ensure the rail remain in gauge.
All very good info
cheers
Phil,