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1st message | this message only posted: 5 Nov 2015 13:27
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Jim Guthrie
United Kingdom

 

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I've just built my first straight switch - I've always used the semi-curved default in Templot up till now.   One thing I noticed when constructing the switch if the tight clearance at the heel of the switch.  I built a 12ft switch and here's the data for it from Templot



I'm using P-32 (1:32 scale) and the switch rail length is 114.3mm and the offset to the inner side of the rail at the heel is 3.57mm - all this checked out on the template and on the switch when I built it.   The problem is that with a rail width of 2.2mm,  that leaves a gap of 1.37mm between the outer edge of the switch rail at the heel and the inner side of the stock rail,  which is less than the check rail gap of 1.5mm.   So it looks as though the back of the flanges would connect with the outside of the switch heel.

I'm modelling the Caledonian and looking at the distance between the switch heels and the stock rails in the pointwork in the pictures of Brechin station trackwork in this message in a thread in the CRA forum...

http://www.crassoc.org.uk/forum/viewtopic.php?f=6&t=415&p=2466&hilit=boxing#p2466

...the distance would appear to be around the width of the rail,  or about 2.2mm in P-32,  which would give more than adequate clearance for the back of the flanges.

Any comments?

Jim.

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2nd message | this message only posted: 5 Nov 2015 13:39
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from:
Nigel Brown
 

 

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Jim

Thinks it's a common problem. I'm into 3mm finescale, and generally move the switch heel at least one sleeper spacing towards the frog. In fact as far as I remember to be on the safe side I use two sleeper spacings (Haven't built any for a bit).

Cheers
Nigel
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3rd message | this message only posted: 5 Nov 2015 14:09
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from:
Jim Guthrie
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Nigel Brown wrote: Thinks it's a common problem. I'm into 3mm finescale, and generally move the switch heel at least one sleeper spacing towards the frog. In fact as far as I remember to be on the safe side I use two sleeper spacings (Haven't built any for a bit).Nigel,

That would be an option for me - extending the length of the switch blade.  Another option I have is a bit of gauge widening.   I'm using Cliff Barker sleeper units to construct interlaced turnouts.  His standard gauge ones I've found to be a bit tight on gauge for ScaleOne32 (P-32 in Templot) so I'm going to have to use his gauge widened sleepers which will give me another 0.5mm of gauge to play with at the switch heel to get a bit more clearance,  although this will mess about with the angles in the switch.

Jim.

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4th message | this message only posted: 5 Nov 2015 14:25
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Martin Wynne
West Of The Severn, United Kingdom



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Hi Jim,

The straight switches in Templot are based on Table 7 in BRT3 (1964).

In the 12ft switch, the virtual switch heel (where the offset is 4.5") is 30" short of the switch rail joint. So the offset at the joint is about 1" wider at 1:32 deflection angle (strictly speaking the section between the heel and the rail joint is curved at the turnout radius). See:



The 4.5" offset, minus 2.75" rail width, would leave the standard 1.75" flangeway clearance between the rails. But because the switch rail is opening 30" further back, the actual open clearance is greater. The usual requirement is 2" clear all along behind an open switch blade, to prevent wheel backs hitting it, which could damage stretcher bars and detection gear.

But if you are modelling the Caledonian, it is quite unlikely that this switch is the correct prototype for you. Ideally you should be creating a custom switch to match your prototype data. Click the set custom switch... button on the switch settings dialog.

Alternatively, detailed drawings of NER pre-grouping loose-heel switches are available in the NERA reprint book, which could be taken as typical.

regards,

Martin.

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5th message | this message only posted: 5 Nov 2015 16:14
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from:
Martin Wynne
West Of The Severn, United Kingdom



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p.s. Jim,

Here is a bit more playing about in Templot. :)

I opened the 12ft switch blade to the usual 4.1/4" opening at the tip by rotating it at the loose-heel rail joint. The grid is in prototype feet, showing 12ft to the heel location and 14ft-6in for the switch-rail length to the rail joint, as listed in the switch data panel:



 
The ruler tool shows the smallest clearance as 0.187ft which is 2.1/4" in real money. That's safely above the prototype minimum of 2".

At 1:32 scale 2.1/4" is 1.78mm, so well above the 1.5mm flangeway for P-32.

Which leaves me a bit puzzled where you are having trouble. On the face of it in a nice large scale such as 1:32 this ought to be doable?

Here is some more info from the Templot Companion web site. I have outlined a bit of it in red. Perhaps I should make this detail more prominent somewhere else in Templot, although I don't know where:



The heel location and the rail joint are separately marked on the templates.

regards,

Martin.

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6th message | this message only posted: 5 Nov 2015 19:27
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from:
Jim Guthrie
United Kingdom

 

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Martin Wynne wrote: Hi Jim,

The straight switches in Templot are based on Table 7 in BRT3 (1964).

In the 12ft switch, the virtual switch heel (where the offset is 4.5") is 30" short of the switch rail joint. So the offset at the joint is about 1" wider at 1:32 deflection angle (strictly speaking the section between the heel and the rail joint is curved at the turnout radius). See:



The 4.5" offset, minus 2.75" rail width, would leave the standard 1.75" flangeway clearance between the rails. But because the switch rail is opening 30" further back, the actual open clearance is greater. The usual requirement is 2" clear all along behind an open switch blade, to prevent wheel backs hitting it, which could damage stretcher bars and detection gear.

But if you are modelling the Caledonian, it is quite unlikely that this switch is the correct prototype for you. Ideally you should be creating a custom switch to match your prototype data. Click the set custom switch... button on the switch settings dialog.

Alternatively, detailed drawings of NER pre-grouping loose-heel switches are available in the NERA reprint book, which could be taken as typical.

Martin,

Thanks for that.   I was labouring under the impression that all straight switches had a blade length to hinge the same length as their name - obviously that doesn't apply to Table 7 in BRT3 (1964).,  and it's got a small bit of a curve as well. :D   The one Caledonian turnout drawing I have has a 12ft straight switch with the toe to heel length of 12 feet and it is all straight.   I've already customised the 12ft straight switch in Templot to use the Caledonian sleepering layout but I used the rail data as supplied.  I'll re-design the rails and use a 1:30 angle (instead of 1:32) which gives 3.81mm heel offset which,  less the rail width of 2.2mm,  gives a gap of 1.61mm which equates to a natz over 2" full size.

I'm now going to have to go and redo sixteen turnouts with their interlaced sleepering.  Hopefully the revised switch won't alter the body of the turnouts too much requiring me to do a pile of timber shoving again. :D

Jim.

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7th message | this message only posted: 5 Nov 2015 19:43
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Martin Wynne
West Of The Severn, United Kingdom



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Jim Guthrie wrote:The one Caledonian turnout drawing I have has a 12ft straight switch with the toe to heel length of 12 feet and it is all straight.Hi Jim,

It's very likely that if the heel is at the rail joint, the clearance there is 2". i.e. a heel offset of 4.3/4" (= 3.77mm in P-32), and the switch angle will be 144 / 4.75 = 1:30.3

Often in such cases the heel joint is supported in a chair, rather than using loose fishplates between timbers.

There was quite a gap between 1923 and 1964. I think the straight switches in BRT3 are an attempt to make the best of what was still left by then, although BR(W) were still using the old GWR loose-heel designs because the GWR never created an 'A' flexible switch.

regards,

Martin.

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8th message | this message only posted: 5 Nov 2015 22:02
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from:
Jim Guthrie
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Martin Wynne wrote: It's very likely that if the heel is at the rail joint, the clearance there is 2". i.e. a heel offset of 4.3/4" (= 3.77mm in P-32), and the switch angle will be 144 / 4.75 = 1:30.3
Martin,

I've re-done the switch to your settings above and it looks fine.  I can also apply it to existing turnouts without messing up my laboriously shoved interlaced sleepers. :D



Jim.

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9th message | this message only posted: 6 Nov 2015 10:48
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John Palmer
 

 

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Martin Wynne wrote: Jim Guthrie wrote:The one Caledonian turnout drawing I have has a 12ft straight switch with the toe to heel length of 12 feet and it is all straight.Hi Jim,

It's very likely that if the heel is at the rail joint, the clearance there is 2". i.e. a heel offset of 4.3/4" (= 3.77mm in P-32), and the switch angle will be 144 / 4.75 = 1:30.3

Often in such cases the heel joint is supported in a chair, rather than using loose fishplates between timbers.

There was quite a gap between 1923 and 1964. I think the straight switches in BRT3 are an attempt to make the best of what was still left by then, although BR(W) were still using the old GWR loose-heel designs because the GWR never created an 'A' flexible switch.

regards,

Martin.
This has been a most interesting thread and Martin’s post above has been extremely helpful: it prompted me to re-visit my custom switch settings and open the heel offset from 4.55” to 4.75”.  This seems appropriate because I have to cater for a heel located at the switch rail joint.

Here is a shot of the resulting custom switch and associated data.  This is intended to represent North British practice, and I am struck by its strong similarities to the Caledonian product Jim is representing.

One possible difference between CR and NBR practice lies in the positioning of the switch rail joint. I cannot call to mind any photograph showing a NB switch where the joint is not located midway between timbers and supported on a heel plate.  This arrangement can be seen in the plan of NBR P&C work at the Old Pway Info website, but the particular switch shown in that plan is 16’ in length with five slide chairs.  Pictures of NB switches of this length seem to be uncommon – the 12’ switch carried on 4 slide chairs seems have seen very widespread adoption.

Poring over pictures of Caledonian pointwork I have yet to seen any evidence of a heel plate being used, and I wonder whether CR practice was to locate the joint in a chair.  Is it correct that in those circumstances there would be no fishplate connection at all between switch and closure rail?  Otherwise there would presumably have to be a special chair at the heel capable of accommodating the fishplates joining these two rails.


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10th message | this message only posted: 6 Nov 2015 12:00
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Jim Guthrie
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John Palmer wrote:
Poring over pictures of Caledonian pointwork I have yet to seen any evidence of a heel plate being used, and I wonder whether CR practice was to locate the joint in a chair.  Is it correct that in those circumstances there would be no fishplate connection at all between switch and closure rail?  Otherwise there would presumably have to be a special chair at the heel capable of accommodating the fishplates joining these two rails.
John,

I acquired a drawing of a Caledonian 12ft switch turnout from another member of the CRA some time ago.  It's not a great drawing since it was a hand trace of an official drawing.  But it does show a hinge joint at the heel of the switch blade and my representation of the switch in Templot (shown earlier) is as close as I could get to this drawing with the positioning of the sleepers.   The switch has four slide chairs each side and a special chair on the fifth sleeper immediately in front of the fishplate joint between the fifth and sixth sleeper spaced at 24" centres.   I'm assuming that this special chair allowed some horizontal play on the switch rail to allow it to pivot at the heel.   This Caledonian drawing seems to be to similar style of construction to the NB 16ft switch (I also have that drawing :) ) allowing for the longer blade and the additional sleeper.  

I will also have another search through all the pictures I can find of Caledonian pointwork to see if I can dig out more detail.  Unfortunately the most promising ones usually have a locomotive parked on them. :)   I do regret not taking details many years ago when I regularly passed a fan of interlaced turnouts in the entrance to Denny Shipyard sidings at Dumbarton.  I reckon they were probably original Caledonian since they were in a very poor state of repair and the Type 2 diesel which occasionally worked them kept a good few wagons as spacers in front of it so that it never had to venture onto the pointwork. :)  

I do wonder why there is so little information on Scottish pre-Grouping pointwork,  especially since interlaced turnouts were being built up to Grouping and there is ample evidence that interlaced turnouts were being maintained and upgraded through LMS and BR days.  Maybe that;s the problem in that the information was still treated as current and not disposed off or archived.   Although I do remember that there was a widespread clearance in the aftermath of the Beeching Report in Glasgow when Buchanan Street and St.Enochs stations were demolished.    St. Enochs had been used as a store for old documentation and it all finished up in skips except for odd bits and pieces which were cherry picked from the skips.

Jim.

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11th message | this message only posted: 6 Nov 2015 12:55
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Martin Wynne
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John Palmer wrote:and I wonder whether CR practice was to locate the joint in a chair.  Is it correct that in those circumstances there would be no fishplate connection at all between switch and closure rail?  Otherwise there would presumably have to be a special chair at the heel capable of accommodating the fishplates joining these two rails.Hi John,

Here is a scan from the NERA book showing the heel joint supported in a chair, with the 2" clearance (i.e. 4.75" offset) shown. There are 4 fish-bolts shown and some sort of fishplate. How this is attached to the chair isn't clear, but I would imagine some sort of back spacer block to maintain the 2" clearance under flange load.

I have been searching for drawings or photos of such chairs, so far without success. As you know, the usual practice of photographers is to wait until there is a locomotive in the way before taking a picture of the track.


Hi Jim,

I've been trying to find the origin of the BRT3 straight switches, likewise without much joy. However here is a GWR 12ft switch, showing the 4.1/2" offset at the virtual heel, and the actual switch rail in this case 2ft-0in longer at 14ft to the joint. Being GWR this is actually a curved switch, rather than straight. Also the GWR love of joggles is evident, drawn somewhat exaggerated:


regards,

Martin.

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12th message | this message only posted: 7 Nov 2015 11:14
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from:
John Palmer
 

 

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Sorry, Jim, I should have paid greater attention to your posts, as you had made it perfectly clear that your switch reflected the Caledonian drawing you held. My surmise that CR practice might be to locate some loose heel joints at a chair was partly driven by examination of the pictures in the thread on the CR Association forum to which you posted a link.  The impression I get is that CR switch design evolved a good deal more than did that on the North British, so apparently widespread was the use of the 12’ NB switch to which I alluded.

The problem I perceive with location of the joint between sleepers is that, unless the heel of the switch is supported by a heel plate such as that used by the North British, the load imposed by a passing wheel will tend to cause the switch to rotate in the vertical plane, the last adjacent chair through which the switch passes acting as a fulcrum. This may have the undesirable effect of causing the toe of the switch to rise above rail level.

On the other hand, the drawing Martin has kindly posted of a heel joint  on a chair shows just how difficult it must have been to mount any kind of spacer block to maintain that 2” clearance.  Those difficulties are exacerbated by the bolts being fed through the fishplate from the side of the adjacent stock rail.  I don’t see how that can be done once the stock rail and closure rail are in place, and it’s an interesting divergence from the North British design, in which the fishbolts  are inserted from the side where there is most room to do so, the nuts then  being offered to the bolts in the gap between stock rail and switch/closure rail.

It is indeed unfortunate that so little information seems to be about regarding pre-group Scottish practice.  I’m so glad that I seized my opportunity to photograph and take some measurements from a North British turnout at Rannoch that was still around in the 1980’s.  Unfortunately, I didn’t know then what I know now, and didn’t take a number of measurements I would subsequently have found useful.  Moreover, some of my measurements in hindsight appear suspect, so I have had on occasion to draw inferences from my photographs and the work of others.  In my defence I plead that throughout my measuring I was under unrelenting attack from a cloud of midges that obviously had a distracting effect!


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Martin Wynne
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John Palmer wrote:The problem I perceive with location of the joint between sleepers is that, unless the heel of the switch is supported by a heel plate such as that used by the North British, the load imposed by a passing wheel will tend to cause the switch to rotate in the vertical plane, the last adjacent chair through which the switch passes acting as a fulcrum. This may have the undesirable effect of causing the toe of the switch to rise above rail level.Hi John,

One function of the stretcher bar(s) is to prevent the switch points from rising under traffic. By running closely under the stock rail, or in older designs through a hole in it.

Some model designs of stretcher bar do not replicate this essential function of a stretcher.

regards,

Martin.

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14th message | this message only posted: 7 Nov 2015 19:30
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Jim Guthrie
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John Palmer wrote: The problem I perceive with location of the joint between sleepers is that, unless the heel of the switch is supported by a heel plate such as that used by the North British, the load imposed by a passing wheel will tend to cause the switch to rotate in the vertical plane, the last adjacent chair through which the switch passes acting as a fulcrum. This may have the undesirable effect of causing the toe of the switch to rise above rail level.


John,

Apart from the action of the tiebar which Martin has referred to,  the closure rail on the other side of the fishplate would also prevent the rotation of the blade around the chair on the toe side of the fishplate.   Also,  most of the time that vehicles would be passing over the blade,  there would be two wheels on the blade, one on each side of the chair,  which would prevent rotation.  It would only be a leading or trailing wheel which would apply an unbalanced weight to the heel end of the blade.

I'll keep digging through the pictures of the Caledonian books I have to see if I can get a good picture of a heel end of a blade.

Jim.

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Martin Wynne
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Hi Jim, John,

Here is C. J. Allen on the subject, in 1915:


He has two chapters on switches, but this is all I can find about loose-heel joints. Unfortunately there is nothing about Scottish practice.

regards,

Martin.

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16th message | this message only posted: 8 Nov 2015 10:10
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John Palmer
 

 

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Jim, Martin,

This is an extract from J.S.Mundrey’s ‘Railway Track Engineering’, substantial parts of which can be previewed on Google Books.  I think it was this that first drew to my attention some of the problems that arise from a wheelset passing over a loose heel joint.

There is also a section  in the HSE’s publication about mine trackwork dealing with loose heel switches containing the following commentary:

“136 A loose heel switch can open inadvertently when a vehicle passes over in the facing direction of travel. This is caused by the guiding wheel on the leading axle passing over the hinged joint and giving it a ‘kick’, which opens the switch slightly , allowing the guiding wheel on the following axle to ‘split the points’. To counteract this effect, switch blades should be longer than the longest wheelbase of any vehicle using the track.”

Despite the focus on keeping switches longer than the longest wheelbase in both these publications, it seems to me that a substantially similar problem must arise when the distance between the trailing wheelset of one vehicle and the leading wheelset of the next is marginally greater than the length of the tongue rail as they make a facing movement through the switch.  Any tendency for a tongue to be displaced by the trailing wheelset in such a case is likely to occur just as the leading wheel of the following vehicle reaches that tongue.

In these circumstances it would appear that the fishplates’ ability to held the tongue rail in alignment is going to be very limited.  Since at least one of these fishplates has been cranked to accommodate the rotation of the switch at the heel joint, there will presumably be little or no clamping of the fishing surfaces on the tongue rail.

I’d hoped I might find a suitable shot of a Caledonian switch In Jim Summers’ lovely book on the company’s signalling, but no such luck.

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17th message | this message only posted: 9 Nov 2015 10:34
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Jim Guthrie
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John Palmer wrote: I’d hoped I might find a suitable shot of a Caledonian switch In Jim Summers’ lovely book on the company’s signalling, but no such luck.
John,

I've had a dig through my Caledonian books - Livery, Wagons, Jumbos, "Branch Lines of Strathearn" and "Caledonian Cavalcade" with not mu8ch luck and a fair bit of annoyance when a potentally good shot has the switch heel just out of frame. :)   However,  I did find one in Caledonian Cavalcade which shows a switch in reasonable detail...


This looks like a fifteen or sixteen foot switch with five slide chairs and the fishplate between sleepers/chairs.   I found another picture of a switch which showed the same details at Almondbank station in the Strathearn book but it was of poorer quality in the shadow of the platform,  so I haven't bothered to scan it.   If I have time I'll try digging back through all my copies of the CRA magazine, "The True Line", because I have memories of pictures of the construction of lines where the intention is to show track and civil engineering work so there are could be better chances of seeing the track details without locos and rolling stock in the way. :)

(I'm also wondering how I am going to model the typical Caledonian stretcher bars. :roll: )

As an aside,  I also found this picture of a GWR loose heel joint in an RMWEB thread which also shows the fishplate between chairs with no other means of support.

http://www.rmweb.co.uk/community/index.php?/topic/56856-midland-railway-prototype-turnout-design-loose-heel-turnouts/#entry700771

I'll also try raising the matter on the Caledonian Railway forum.

Jim.

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Trevor Walling
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Hello Jim,
              (I'm also wondering how I am going to model the typical Caledonian stretcher bars. :roll: )I seem to recall seeing it done by inserting them into insulating bushes fitted to each blade.
Page 105 An Approach to Building Finescale Track in 4mm by Iain Rice
Regards.:)

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Jim Guthrie
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Trevor Walling wrote: I seem to recall seeing it done by inserting them into insulating bushes fitted to each blade.
Page 105 An Approach to Building Finescale Track in 4mm by Iain Rice
Regards.:)
Trevor,

You reminded me that I got a copy of this book many years ago and I've just dug it out. :)   It gives me some confidence that it can be done in smaller scales but I will want it to be fully functional in 1:32 scale so I may investigate using brass rod and countersunk 10 or 12BA screws to lock the bars to the switch blades.   Insulating the stretcher rods should not be too difficult although the Caledonian's predilection for boarding and boxing in point rodding in the four and six foot way would help to disguise any method used. :D

Jim.

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Jim,

I agree that the Cavalcade shot appears to show a rather longer than twelve foot tongue rail, and 15'-16' looks about right to me.  No sign of any heel plate below the joint, and, judging by the prominence of these in pictures showing North British switches, such a plate would be pretty obvious if present.  I suspect, therefore, that heel plates didn't find their way into Caledonian practice.  I also wonder whether the North British found their adoption so beneficial as to have stultified improvements to switch design, with the consequence that the NB 12' heel plated switch is all you ever see.

As can be seen in the picture in your link, the GW loose heel switches receive additional restraint from the attached rods that pass through slots in the adjacent stock rail.  I think this feature may be unique to the GWR.

Almost completely off topic, I happened across John Frankenheimer's film 'The Train' on Youtube today.  The film's Rive Reine was shot at Acquigny in Normandy and, if you freeze the footage where the Ouest 0-3-0 is derailed at the yard throat, you get a good view of interlaced timbering on the turnouts there!

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from:
Simon Dunkley
Oakham, United Kingdom



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From the CRA forum, the following image suggests that the 12’ foot switches had the joint in a chair, but were for sidings. That may reflect changing usage over time, as new designs came on stream.
https://www.crassoc.org.uk/forum/download/file.php?id=101
Also, the oldpway.info site suggests longer switches, 32’ in this case, on main running lines. Joint is between the chairs.
http://www.oldpway.info/drawings/1900pc_pl01_CalR_pnts.pdf

From 12’ to 32’ is quite a big step (20’, to be precise!) so I wonder if there was something in between the two: the photos seem to suggest that. 
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