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topic: 2460Station Throat Timbering
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posted: 16 May 2014 22:20

from:

Michael Woolford
 
Swindon - United Kingdom

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Since my plan is now finished, other than the turntable and back road, I would like to start work on the timbering. I have looked through a few topics on here to see what I could find out, but I have come to find that it is very much a black art, especially in more complex areas. I am modelling the end of the LMS into Nationalisation and would like some information on their practices when it comes to the alignment of timbers. One of the first things I need to do is choose between square on/equalised timbering. Any info re the correct way of doing things? I have also attached the box file. Thanks in advance.

Michael
Attachment: attach_1852_2460_Station_Layout_16May14.box     417
Last edited on 16 May 2014 22:58 by Michael Woolford
posted: 18 May 2014 13:14

from:

Martin Wynne
 
West Of The Severn - United Kingdom

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Michael Woolford wrote:
One of the first things I need to do is choose between square on/equalised timbering. Any info re the correct way of doing things?
Hi Michael,

I don't think you should assume that there is a "correct" answer to this. Everything depends on the period but mostly on the individual site conditions and traffic flows.

For the timbering of a station throat no two locations will be the same. Diamond-crossings and slips are always equalized, at least within the middle section, because it is practically impossible to get all the K-crossing rail-fixings in the correct place if the timbers are square-on to one of the roads. Which means that it is easier to arrange the timbering of any connected turnouts if they are also equalized.

For a traditional steam-era bullhead railway, my preference is to start equalized and only change it for say, running line crossovers. Until Templot2 the default in Templot was equalized. The equalized style generally allows fewer long timbers to be needed and less timber shoving.

For modern flat-bottom track you will probably want to start square-on and only change it for diamonds and slips.

The special crossing chairs must fit the rails in the specified positions, and must have a timber under them. This generally limits you for the amount by which the timbers under a V-crossing can be moved forward or back. These will generally be the Y - X - A - B - C timbers*. But you can skew them a bit more or less, and shorten them or lengthen them under an adjacent track, so that a timber comes under the correct crossing chair positions for several V-crossings. Placing short timbers end-to-end, or long timbers side-by-side makes it much more difficult for them to be packed and tamped.

Skewing timbers is called "twist" in Templot's shove timber functions, using the twist mouse action or the cw and acw buttons -- which rotate the selected timber by 1 degree of angle for each click, or each press on the C and A keys.

* bullhead V-crossing chairs:
1:4:                   X - A - B
up to 1:6:             X - A - B - C
1:6.5:             Y - X - A - B - C
up to 1:8.5:       Y - X - A - B - C - D
up to 1:10.5:      Y - X - A - B - C - D - E
1:11:          Z - Y - X - A - B - C - D - E
up to 1:12:    Z - Y - X - A - B - C - D - E - F

(These letters are on the templates as a suffix on the timber number. The A timber is always under the blunt nose of the vee.)

Here's some text that I have posted a few times:



Timbering style is a frequently asked question, because there is no clear answer. Generally speaking, equalized timbering was the norm in the pre-grouping period (before the 1920s), and square-on timbering is the standard now. Between then and now you get both. The change was gradual and varied in pace according to local practice. For much of the post-grouping steam era it would be common to see square-on used for main running lines, with older equalized timbered turnouts predominating in yards, sidings and branch lines.

(Except on the GWR, where there is evidence of the exact opposite! Early turnout drawings show a square-on style, but when the flexible switches were introduced in 1930, the drawings show equalized. In many cases it seems simply that the preference of the local relaying inspector was the deciding factor.)

There are several factors at work here. The main reasons for using a square-on timbering style are:

1. The main road is "stronger" in the sense that it is held to gauge with timbers at right-angles to the rails. This is always desirable for robust track. If timbers are skewed to the rails there is a much greater risk of gauge-spread, especially on curves. So if the main road of a turnout is a running line (and especially if it is on a curve), and the turnout road is a low-speed crossover or branch line, it makes sense to use the square-on arrangement to concentrate strength in the more heavily used road.

On the other hand, if both roads are running lines of similar importance, you would want to have some strength in both roads and an equalized timbering arrangement is then the best option.

2. Where pointwork is prefabricated in the works, dismantled and delivered to site as a kit of parts, with the rail-fixings already attached to the timbers, it is much easier to set out the timbers at the correct specified spacings if the timbers are all parallel to one another and square to the main rails.

3. For modern mechanised maintenance and tamping equipment, it is essential that the timbers are parallel to one another and square-on.

The disadvantage with square-on is that some rails are at a significant angle to the timbers. The chairs or baseplates at the V-crossing must fit the rails at the specified positions. This means that it can be difficult to position square-on timbering to support all the rails in the proper place, and occasionally extra timbers or wider ones have to be used to ensure that no chair screws are too close to the edge of a timber.

Which explains why equalized timbering was used in the first place, in the days when pointwork was laid out and assembled on site by the local gang. It makes it much easier to get all the chairs properly supported, and it doesn't matter too much if an odd timber is an inch out of position. It also means that the two check rails are both in the same position relative to the V-crossing (frog) for traffic on each road. Nowadays check rails are quite long, so that doesn't matter so much.

Diamond-crossings and slips are always equalized, as it is practically impossible to get all the K-crossing rail-fixings in the correct place if the timbers are square-on to one of the roads.

Complex junctions and station throats often require considerable ingenuity in laying out the timbering, to ensure that all rail-fixings are in the correct place on the rails, and properly supported, and that all timbers can be tamped. The timbering design of a complex layout was something of a black art. And with Templot's Shove Timber functions you can learn all about it! :)

Having decided on square-on or equalized style, you then need to decide between in-line or centralized timber ends. More about that in this group message:

http://groups.yahoo.com/group/templot/message/773

There is also a lot of further discussion about timbering in this group sequence:

http://groups.yahoo.com/group/templot/messages/2053?expand=1

Apart from equalized-incremental and square-on, Templot also has two further timbering styles - equalized constant and angled-on. These are intended for use when you are using superimposed partial templates, as an aid to subsequent timber shoving. (Equalized constant is also used for half-diamonds, of course.) I'm not aware that either of these styles would ever be correct for a single turnout - unless anyone knows otherwise?

Martin.

posted: 18 May 2014 13:42

from:

Martin Wynne
 
West Of The Severn - United Kingdom

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p.s. Michael,

I have just had a look at your plan and noticed that you do not have a 6ft way minimum running clearance at this location (see the spacing ring):

2_180834_270000000.png2_180834_270000000.png

By easing that turnout from 1:6 to say 1:7 you can probably cure this (and also ease the sharp radius in the turnout).

Click the p-s pre-set button on the spacing-ring dialog to set the ring to 6ft way for your current scale and gauge.

"6ft way" means the tracks are at 11ft-2in centres. The actual gap between the rails will be more than 6ft when using an under-scale track gauge such as 00, EM, 0-MF, etc. Here for EM the required gap (for BS-95R rail, 2.75" wide) is 24.63mm, as you can see. And you may want to increase that for a running clearance on sharp curves -- use the dummy vehicle tool to check.

regards,

Martin.

posted: 20 May 2014 11:13

from:

Michael Woolford
 
Swindon - United Kingdom

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Hi Martin,

Many thanks for that, I'm sure I will end up reading through your post several times. There is a lot of useful info there to take in. I'm sure that I will be asking for help again when I become stuck! I'll just have to give it a go and hope that it looks ok.

Also, thanks for pointing out the narrow track spacing at the point you highlighted. I will try your suggestion and see if it works. I was actually thinking about trying to change some of the B6 turnouts to B7s to try and aid smoother running.

Michael

posted: 20 Jul 2014 17:21

from:

Michael Woolford
 
Swindon - United Kingdom

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I have finally had a chance to look at the timbering after two months away from Templot. I have found myself in a situation where the same two timbers of a B8 crossover conflict each other, but cannot be moved as they are the two crossing timbers that support the crossing vees with a 'D' chair. Any suggestions on how to arrange the timbers so that they don't conflict and are still in the correct position relative to the crossing vees?2786_201221_040000000.png2786_201221_040000000.png

Michael

posted: 20 Jul 2014 18:40

from:

Martin Wynne
 
West Of The Severn - United Kingdom

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Michael Woolford wrote:
Any suggestions on how to arrange the timbers so that they don't conflict and are still in the correct position relative to the crossing vees?
Hi Michael,

Omit one of the timbers, extend the other one, and then twist it slightly so that it supports both D chair positions at 1 and 2:

2_201336_520000000.png2_201336_520000000.png

regards,

Martin.

posted: 20 Jul 2014 20:04

from:

Michael Woolford
 
Swindon - United Kingdom

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Martin, many thanks for that, I have now got that part sorted. Do you, or anyone else, have any idea if it is acceptable to have a timber under a rail that it is not supporting so that there is sufficient timber extending from the rail that it is supporting? I ask this because I am trying to avoid the use of long timbers where there is an alternative as I know that this is what would have taken place due to the cost and size/weight of the long timbers.

Is there actually a minimum length of the extension of the timber, beyond the rail that one end is supporting? I was thinking that perhaps it is possible to butt two timbers together that can't be moved so that they join end-to-end, while not being in line with each other.

Michael
Last edited on 20 Jul 2014 20:20 by Michael Woolford
posted: 20 Jul 2014 20:27

from:

Michael Woolford
 
Swindon - United Kingdom

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I just thought some additional information might help as to the reason behind my queries. The situation I have is where there are two crossovers that are parallel to each other. Perhaps it is therefore acceptable to use long timbers to support all of the rails in certain positions? The other alternative is to replace the long timbers at the heel end of the turnouts with individual timbers, and twist the timbers that are supporting the rails connecting the crossover.

Michael
Last edited on 20 Jul 2014 20:28 by Michael Woolford
posted: 21 Jul 2014 12:02

from:

Martin Wynne
 
West Of The Severn - United Kingdom

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Hi Michael,

It is certainly acceptable to have a timber running under a rail without a chair, provided the rail is adequately supported in other chairs on each side.

I'm not too clear what you are asking about long timbers -- it is normal to have several long timbers at the centre of a crossover. That's why Templot leaves a gap for the opposite timbers to be extended into. How many long timbers varies with different prototype companies.

It's not usual to have two separate timbers end-to-end because it makes packing difficult. If a long timber is not available, the two shorter timbers would be half-spliced together to make a single long timber. The joint is often made by bolting old fishplates top and bottom through the splice. A detail not often modelled.

If you post a screenshot we can see more clearly what you are asking.

regards,

Martin.

posted: 21 Jul 2014 13:38

from:

Michael Woolford
 
Swindon - United Kingdom

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2786_210728_100000000.png2786_210728_100000000.png

This screenshot shows the layout of the crossovers that I have been referring to. You can see that there are two separate crossovers that have both sets of long timbers conflicting each other in certain positions.

Michael
Last edited on 21 Jul 2014 13:39 by Michael Woolford
posted: 21 Jul 2014 14:02

from:

Martin Wynne
 
West Of The Severn - United Kingdom

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Michael Woolford wrote:
This screenshot shows the layout of the crossovers that I have been referring to. You can see that there are two separate crossovers that have both sets of long timbers conflicting each other in certain positions.
Hi Michael,

The position of these long timbers is not critical -- they are carrying only plain chairs.

You can therefore move them forward and back as necessary until they do not conflict. You could also shorten them a little if necessary. Ideally the spacings should be not more than 25" centres at the rail joints.

2_210851_200000000.png2_210851_200000000.png

You could argue that some of them should be replaced with plain sleepers where you have a wide crossover. This will depend on the practice of the prototype company. Possibly one long timber across all three tracks at the centre, and the rest as plain sleepers.

regards,

Martin.

posted: 21 Jul 2014 18:52

from:

Michael Woolford
 
Swindon - United Kingdom

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I think I have managed to achieve something that is acceptable; it's taken two days to get it to this stage with thanks to Martin. 
2786_211343_240000000.png2786_211343_240000000.png

You will see that I have made use of Martin's suggestion to use two long timbers joined together in a few places, although I'm sure I could have used just the two individual long timbers in a couple of locations. It does however, give me the opportunity to add the extra detail at the joint, which, even if it is rarely modeled, I will do my best to replicate it. Does anyone have any photographic examples of jointed timbers that they would be kind enough to share?

Many thanks for your help so far Martin, it's greatly appreciated. 

Michael
Last edited on 21 Jul 2014 18:53 by Michael Woolford


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