GWR Switch & Crossing.... still learning after all these years

Dog Star

Western Thunderer
This soul searching is all down to that S7 modeller of a GWR Edwardian "Bacon, Lettuce and Tomato" layout, Mr. Chris Brown (@ChrisBr) with Henley-in-Arden before 1908 (and the opening of the North Warwickshire line). All I did was to suggest that he had got the wrong style of GWR plain line chairs as the Exactoscale GWR 2-bolt chair was for the post 1900 "00" rail section whereas a closer to type chair was the C&L GWR 2-bolt chair for the GWR 95 rail section - given that the branch line terminus was built in the 1880s then the C&L chair is a better "fit" than the Exactoscale product.

OK, we got over that molehill and Chris has been doing some excellent work on a 3D-printed version of the GWR crossing nose chair from the Victorian-period given that the C&L slab and bracket alternative is too modern for a 19th century BLT. So I popped down to look at the samples recently, over coffee Chris talked about drawing / printing some of the other crossing chairs... I nodded in all of the appropriate pauses when a comment about L1 (Bridge) chairs struck with some force. Roughly put, Chris was quoting from the GWSG tome on GWR S&C Practice and saying that the L1 chair was not used prior to early 1930s, hence the need for a fair number of different block chair types for a common crossing. I agreed and then realised the significance of the statement.

Oh dear, whilst L1 chairs do get used for reasons of space in chairing a common crossing the L1 chairs also get used in other situations... for example:- to support rails alongside engine pits, for rails on longitudinal woodwork on steel bridges, where there is conflict between chairs adjacent to the joint between switch and closure rails.

So what did the GWR head-ganger do in the Victorian / Edwardian period before one of their number spotted the L1 chair in the stores inventory? Strange this, I had the answer without knowing the question; use narrow chairs fitted side-by-side on the same timber. Those of you who have been with me so far, and I mean back to round about page 11 of the story of Hartley Hill, ought to be saying something like: - "Oh yes, the GWR just copied the LNWR way of doing things" and that was to fit two (narrow) chairs side by side where standard chairs would not work.

A quick count up of how many such chairs in a typical LNWR turnout gave way to raised eye-brows - a couple of dozen chairs and producing such GWR "Z" chairs by reducing the width of C&L 2-bolt chairs with a 50% failure rate equates to a lot of sweat, swarf and failed attempts. To his credit Chris spotted the concern in my glazed eyes and suggested that maybe doing a 3D drawing of a z-chair ought to take precedence over further crossing chairs. Nice chap.

And now for the reason for this post!

Received wisdom for timbering of GWR turnouts is 14" under the crossing nose and switch toe with 12" under all of the other chairs in the formation. I have no reason to doubt this for post 1930s work where the L1 chair is in use. However, when considering the timbers for turnouts where the Z-chair is being used in "side-by-side" fashion for switch and closure rails close to the switch heel then the GWSG tome indicates that the GWR would have (ought to have) used 14" timbering (as per the LNWR for which I have copies of S&C drawings circa 1909 and those are marked for 14" timbers throughout a turnout). So Chris and I spent a couple of hours peering at images (spread across Warwickshire Railways where Z chairs are visible and Railway Archive websites) and have not done too well in identifying 14" timbers in the area of the switch heel. We can now spot the Z-chair in side-by-side use by looking for a chair which is significantly closer to one edge of the timber than the other - not so easy to decide if the timber, upon which a Z-chair is sitting off-centre, is 12" wide or 14" wide.

Anyone any information on use of 14" timbers within GWR S&C work of the period 1880 to 1910?

thanks, Graham
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Western Thunderer

You may already be aware but there is a little info (probably not relevant) here

Link no longer valid. Contact me by PM for a copy fpu.
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Western Thunderer

Graham and I are both aware of this excellent publication (in fact it is the only source of information I have found so far on the 3C chair which preceded the Slab and Bracket chairs).
Re-reading it again, there would appear to be 2 relevant sentences - "The sleepers are 12 x 6 inches except that under the v chair, which is 14 x 6 inches" and "Following this, ordinary chairs are used through the turnout until the crossing is reached, when special chairs come into use again." which comes just after a description of the special switch chairs. However there does seem to be photographic evidence of Z type chairs being used in S&C work in at least some formations, so the question remains, 12 or 14?




Western Thunderer
Dave (@daifly), the link is broken, please can you repair?
Hi Graham
Unfortunately not. It was a link to a Dropbox account (now unavailable) which may have been Pete Spellers and that contained all of the Swindon Engineering Society Papers that had been found at that time. Me being me, I downloaded the lot so I'll send you a PM with a copy fpu.
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Phil O

Western Thunderer
Not spotted this thread before, but on the old Templot Forum, I made a number of posts with pictures of quite a number of GW special chairs, that were extant and may still be in use on the ESR at Cranmore. To find them you need to type "GW special chairs " in the search box, top right of the home screen. The " quote commas are important, to find the posts. All the photos were taken when I was in the track gang.

Dog Star

Western Thunderer
Four years on since Chris summarised the conundrum... 12" or 14" under a Z chair? I ought to have added Z alongside Z chair or Z alongside plain line chair (you can get Z plus Z on a 12" timber, Z plus plain line chair requires 14" timber).

For those of you who follow Spike's (@Spike) tales from the folding table, recent posts have told of an extension to Scruft's Junction... a colliery is being added to the end of the layout. I have been given the task of building the trackwork and the first piece of new track is a turnout to form the empties road. Given that the new turnout is considered as railway property the need has arisen to resolve the "condudrum". Over the last few days I have gone back to "GW Switch & Crossing Practice" by David J Smith (pub. GWSG) and extracted what information seemed relevant to the question of Z chairs and 12" / 14" timbers - that information and my conclusions are presented here. Comments / suggestions appreciated.

Precis from GW S&C Practice
1/ The arrangement for timbers / chairs / rails for old type switches is shown in Fig.5 (on page 15), that drawing shows the post 1933 arrangement with notes that summarise the changes from earlier practice, the notes of relevance to this discussion are:-

* replace L1 chairs by ordinary plain line chairs and Z chairs;
* use 14" timbers at switch toe;
* use 14" timbers with Z chairs adjacent to switch heel
(and by implication, a 14" timber under the far end of the stock rails - the dwg. shows a L1 chair next to the rail joint between the turnout and plain line track).

[my comment - the book recognises that, at some point before 1933, a 14" timber is used to support a Z chair alongside a plain line chair... as far as I can see this section of the book does not consider the possibility of Z chair alongside Z chair on a 12" timber which is surprising given the economics of 12" against 14" timber.]

2/ Early practice for crossing timbers (circa 1900) has... 14" timber under crossing nose and 12" timber otherwise throughout the turnout" (page 81).

[my comment - if this statement is correct then the chairing adjacent to the switch heel has to be Z+Z rather than Z+ordinary chair (which appears to be in conflict with note 1 above).

Further use made of 14" timber at this time... (page 81).

(my comment - I think "at this time" means "early 1920s" given the context of the statement)

used beyond the 1S/2S/3S chairs to allow use of ordinary plain line chair alongside Z chair... (page 81).

[my comment - these statements taken together imply that earlier practice had been Z+Z on 12". The context of the last statement above is the only place in the book where the text describes which type of chair is under the stock rail (plain line) and which is under the closure rail (Z).

3/ In the section dealing with chairs... the sub-section about "Other Chairs".

"the Z chair for use with 14" timbers... {chair is} only 6" wide... where space precluded use of ordinary chairs (7 1/2" wide)".

"L1 chairs introduced in 1933 with appearance of flexible switches and adoption of 12" timbers for most purposes"

[my comment - I interpret the first statement as saying that (a) Z chairs were used where space precluded plain line chair alongside plain line chair and (b) the use of Z chair alongside plain line chair required 14" timbers. The second statement links the introduction of the L1 bridge chair with the change from 14" timbers to 12" timbers and the move away from Z chairs for new work.]

So what do I make of all of this? First, the turnout arrangement drawing here shows 14" timbers supporting Z and plain line chairs... not L1. The drawing looks official and I am minded to treat the information as pukka. However, the drawing conflict with note 3 above. The only way in which I can see these texts working is if Z+Z on 12" existed between 1900 and grouping with Z+plain line on 14" used for new work between grouping and 1933 whereupon L1 took over and 12" replaced the 14".

David Smith summarises the sources that he used in writing the book and predominately those sources are from the 1930s onwards, how that material relates to times earlier is dependent upon additions to stock parts and changes to design concepts - in the case of 12" or 14" timbers in the proximity of the switch heel the use of 12" or 14" is driven by the chair types available and the introduction of the L1 chair puts a peg in the ground. Just when changes were made previous to the use of the L1 chair is not so definitive. My take on the matter as relevant to standard leads is this:-

1/ by the beginning of the 20th century the GWR had standardised on 12" timbers throughout a turnout with the exception of a single 14" timber which was located under the nose of the common crossing. Where the proximity of stock rail and closure rail did not permit of plain line chair under each rail then the PW engineer would use a Z chair under each rail.

2/ at some date in the early 20th century, possibly in the early 1920s, the GWR moved to using Z chairs alongside plain line chairs and that move dictated that some 12" timbers were replaced by 14" timbers (12" timber not wide enough for Z chair alongside plain line chair).

3/ in the early 1930s the GWR began to use the L1 ("bridge") chair in standard leads, the length of the L1 chair at 10 1/2", being less than that of the 95R chair at 1' 2 1/2", permitted L1 chairs on 12" timbers to be placed under stock and closure rails without conflict.

Photographic evidence

Edwardian Enterprise (Norris, Beale and Lewis, pub. Wild Swan) has two photos which illustrate the use of Z chairs.

1/ Page 150 - the location of this photo is the north end of the down platform loop at Ruislip & Ickenham station, date is 1906 to circa 1914. The photo shows how a Z chair sits to one side of a timber.

2/ Page 170 - the turnout to bottom LH corner, this appears to show Z chairs, on 12" timbers, for both stock rail and closure rail.

I shall be using 12" timbers and Z+Z chairing for the turnouts at the entrance to the empties road and exit from the fulls roads - with 3D printed chairs for all of the S&C fittings bar the plain line chairs. A preliminary step was to prepare a plan showing arrangement of chairs and timbers... and work stalled pending resolution of the matter of the Z chairs. No excuse now.
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Western Thunderer

Looking at the Worthington 1900 IRC Report, documentation shows that the GWR was using a 14" wide sleeper under the crossing nose, and 12" sleepers elsewhere as you mention above. Additionally, his drawing does not show a "Z chair" but a No.6 chair on the wing rails, where bridge/Z chairs may have been used in later years, on the crossing vee side of the fishplates. Unfortunately he does not show the closure rail sides of the crossing, which may have used the "Z chairs" At this time, the LNWR was using bridge chairs, whereas the LYR was using narrow chairs side by side. The GNR was doing similar, as it had for many years, but with 16" wide sleepers.

I hope the links above prove useful.


Dog Star

Western Thunderer
Ian (@Lancastrian), thank you for your reminder to readers about the International Railway Congress , Paris, 1900, reports which are available from Ernest Bate's web site, much to read for those who are interested in PW of that period.

I can "see" the pages for the switches and for the checkrails... the page for the crossing displays as a blank page. Can you assist with a visible copy?

regards, Graham

Dog Star

Western Thunderer
I shall be using 12" timbers and Z+Z chairing for the turnouts at the entrance to the empties road and exit from the fulls roads - with 3D printed chairs for all of the S&C fittings bar the plain line chairs. A preliminary step was to prepare a plan showing arrangement of chairs and timbers... and work stalled pending resolution of the matter of the Z chairs.
Well that good intention went far left field for some months.

Chris Brown (@ChrisBr) drew up and then arranged for printing of all of the S&C chairs for a GWR 1:7 crossing and 12' loose heel switches. Timbers cut and stuck to a Templot plan, rails cut to approximate length and building began just before last Christmas. After a couple of weeks work there was a chaired and keyed common crossing alongside of stock rails, check rails with keys added to the formation and a start was made on the switches and closure rails. Progress with the crossing and switch parts of the turnout shall remain off-piste for now pending completion of the whole turnout.

However, those pesky Zs came home to roost as the arrangement of the Zs began to introduce doubts into the construction. I have cited, earlier in this topic, pages in "Edwardian Enterprise" where one can see circa 1900 GWR turnouts with Z chairs used in the vicinity of the loose-heel of the switch rails. Consider how those Zs might be placed on a 12" timber, one for the stock rail and one for the closure rail - ah, yes, so which is closer to the switch heel... the Z chair for the closure rail or the Z chair for the stock rail. After making the decision about the switch / stock pair on one side of the turnout then what is the arrangement of Zs for the other switch/stock pair?

Going back to the photos in "Edwardian Enterprise" and with decisions made about how the Z chairs are placed just after the 1S/2S/3S (if required), those photos threw the proverbial spanner... the placement of Zs before the fishplate on the stock rail is changed after the fishplate! I shall refrain from postulating any further on this subject because, at this time, I do not understand why such changes are needed.

So to some photos, the currency of WT. Chris Brown and I went hunting 1S and 2S chairs at Didcot, some success and some further questions. Our first action was to review what is in the PW park for S&C fittings - no luck. Next was to check on a turnout adjacent to the turntable... this was laid in post installation of the turntable so no historical context. Bingo, a turnout with 14'0" switches and loose heels... and twenty Z chairs. Here are some photos of those Z chairs.

This is the right hand switch / stock rail pair with the loose heel between the 1S (not visible) and 2S chairs. Here the first Z chair is on the stock rail (straight lead) and the second Z chair is on the closure rail (diverging lead), both Z chairs are on the same 12" timber.

This is the right hand stock / closure pair again, further towards the crossing, the fishplate is on the stock rail. Note how the Z chair arrangement changes... the left hand pair of Zs has the stock rail Z leading whilst the right hand pair of Zs has the closure rail leading. This change in Z placing is what can be seen in the Edwardian Enterprise pages.

Ah, but...

I suspect that the Didcot PW crew did not pay too much attention to the niceties of GW Edwardian S&C practices after all this turnout could well have been installed before the GWSG published Smith's book on the subject.

To complete, there is a catch point in the coal stage road and that is also a 14'0" loose-heel switch... in this case there is a fair chance that the catch has historical context.

regards, Graham