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page trail:  Templot Club > Forums > Baffled beginners > sleeper interlacing - Midland Railway stretcher bars
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                                       sleeper interlacing - Midland Railway stretcher bars
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41st message | this message only posted: 21 Oct 2017 09:46
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from:
Tim Lee
London, United Kingdom

 

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Here is another example which also appears to have the rodding unconnected with the stretcher bars
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42nd message | this message only posted: 21 Oct 2017 10:17
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from:
Ariels Girdle
 

 

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I tend to agree. You seem to be opening up a real can of worms here.
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43rd message | this message only posted: 21 Oct 2017 11:26
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John Palmer
 

 

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The purpose of detection is to prove that a point tongue has assumed the correct position for clearance of its related signal. For this reason a detector rod is connected to a point tongue (toe of switch), rather than to the stretcher bar. If the detector rod were attached to the stretcher bar and that stretcher had become disconnected from its associated switch rails, detection would prove nothing about the position of the switch tongues.

In the Getty image, the detector rod is attached to the open switch tongue furthest from the detector This is consistent with the adjacent ground signal reading only over one route, probably that diverging to the left. Assuming the picture shows both signal and points in the 'normal' position, the detection arrangement proves that the tongue shown open in the picture has nestled in the closed position against its adjacent stock rail when the points are reversed, and that the associated signal can be cleared. It may be of interest that the IRSE booklet dealing with detection (1969 edition) suggests that in a comparable situation the normal arrangement would be to connect the detector blade to the normally closed switch tongue.

If the signal for which detection is provided reads over both routes through the points detected, then blades for both switch tongues will be provided in the detector and connected to their respective tongues by independent rods.

It seems to me that there is a flaw in the logic of detecting one tongue only. In such a case, if the undetected tongue has become disconnected from its stretcher you may end up with both tongues in the open position or both in the closed position (depending on which tongue has become disconnected). Detection then provides false 'proof' that the points have assumed the correct position, but a derailment on the switch has become almost inevitable.

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44th message | this message only posted: 21 Oct 2017 11:33
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Tim Lee
London, United Kingdom

 

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Thanks John,

Glad I was reading the arrangement correctly ... appreciate the explanation - I now have a better handle on why!
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45th message | this message only posted: 21 Oct 2017 11:45
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from:
Martin Wynne
West Of The Severn, United Kingdom



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John Palmer wrote: It seems to me that there is a flaw in the logic of detecting one tongue only. In such a case, if the undetected tongue has become disconnected from its stretcher you may end up with both tongues in the open position or both in the closed position (depending on which tongue has become disconnected). Detection then provides false 'proof' that the points have assumed the correct position, but a derailment on the switch has become almost inevitable.Hi John,

In the early days there was little thought about disconnected or broken stretcher rods. On the face of it, that should be a very unlikely occurrence given the amount of staff then available for track maintenance. Nowadays we know different after recent major incidents:

 https://assets.digital.cabinet-office.gov.uk/media/547c9037ed915d4c0d000199/R202008_081023_Grayrigg_v5.pdf

The important thing then was to detect that the relevant switch blade was properly closed against the stock rail, before the signal can clear. That's something beyond mechanical failure, and much more likely to go wrong, such as weather conditions or fallen debris affecting the rodding run or clogging the switch blade.

regards,

Martin.


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46th message | this message only posted: 21 Oct 2017 12:07
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from:
Tim Lee
London, United Kingdom

 

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Here is another image which again shows the 180 degree actuation rod bend locating into the switch independent of the front stretcher bar. Masborough, 1907 It does seem to suggest that pre WWI at least the Midland connected rodding independently of the front stretcher bar certainly within sidings and goods yards. I am still hoping to turn up a mainline trailing turnout to see if the practice differed  - we know it was different for facing due to the requirement for locking.



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47th message | this message only posted: 21 Oct 2017 14:20
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from:
John Palmer
 

 

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Martin Wynne wrote: In the early days there was little thought about disconnected or broken stretcher rods. On the face of it, that should be a very unlikely occurrence given the amount of staff then available for track maintenance. Nowadays we know different after recent major incidents:

 https://assets.digital.cabinet-office.gov.uk/media/547c9037ed915d4c0d000199/R202008_081023_Grayrigg_v5.pd
Indeed, Martin, and it was not merely the number of available staff that mitigated the risk, but the frequency of inspection. I understand that a daily inspection of running lines had become accepted practice by the mid 1860's, but that state of affairs has to be contrasted with the regime in place by the time of Grayrigg, as the report you linked indicates that “For Category 1 track, inspections were required weekly with a maximum interval between inspections of eight days.” This represented a major change that could be justified by the greater reliability of modern track, but which nonetheless enlarged the risk of defects that might have become apparent from a daily inspection remaining undetected for extended periods – as at Grayrigg.


I may have misinterpreted the IRSE's suggestion as to which tongue should be detected in a single detection arrangement. Looking at 'Railway Signalling and Communications', it seems that the tongue to be detected in such a case is the one that needs to be closed in order for the related signal to be cleared. Generally this will be the tongue that is open when the switch lies normal. I don't think this affects my conclusion that the logic is flawed, inasmuch as any failure of both tongues to move creates the conditions for a derailment, regardless of whether such failure results from disconnection of tongue from stretcher, weather-related reasons or debris fouling the connections.

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48th message | this message only posted: 22 Oct 2017 08:06
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from:
Tim Lee
London, United Kingdom

 

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Next Question ......
If we assume that for sidings etc at least, pre WWI turnouts were activated by an independent fixing of the point rodding to the nearest switch blade, can we assume that the rod itself would prevent the point blade rising or moving in relation to the stock rail (apart from laterally). 
If this is the case, and looking at the drawing which Martin posted earlier -

would it be right to assume that the extension shown on the right hand side of the drawing projecting through the stock rail, achieves the same thing on the side opposite to the actuation rod?

Edit - correction, looking again at the drawing it would appear that there is no extension through the stock rail - I assume therefore that the switchblade relies on the undercut of the planing to ensure against lift? Am I right in assuming that the extension is primarily used where the stock rail is joggled?

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49th message | this message only posted: 23 Oct 2017 14:16
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from:
Tim Lee
London, United Kingdom

 

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A couple of further images which might suggest this practice on rodding was not limited to sidings etc.


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50th message | this message only posted: 23 Oct 2017 14:45
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from:
Martin Wynne
West Of The Severn, United Kingdom



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Hi Tim,
 
Interesting that in the first pic there are 2 timbers in the switch front. In the second pic only 1 timber. Something else to get right, when adding the fishplates.
 
Nowadays the switch front timbers are indeed timbers (12" wide). In pre-group days they were often plain sleepers (10" wide). Templot does include an option for this in the custom switch settings.
 
So that's two more things to get exactly right in the face of conflicting evidence.
 
Anyone got a pic showing a switch front of 2 timbers, one a timber and the other a sleeper?
 
regards,
 
Martin.

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51st message | this message only posted: 23 Oct 2017 19:14
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from:
Tim Lee
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Thought it might be useful to load this MR drawing of switch blades and stretcher bars for information.
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Attachment: DSC_0012.JPG (Downloaded 24 times)
 
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52nd message | this message only posted: 30 Oct 2017 09:07
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Tim Lee
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Does anybody have any drawings or images which might describe the connection for circular bar rodding to an intemediary crank within the rod length when two sets of points have to work together ... ie for a crossover on running lines. I am trying to work out how the connection from the bar would have been worked (easy to find examples of channel rodding but not circular).
It is the equivalent of this connection but to a bar I am looking for


Used to move the crank 'B' on the attached diagram



Thanks

Tim

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53rd message | this message only posted: 30 Oct 2017 14:08
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Tim Lee
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I have been kindly sent these ... so all good
Tim





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54th message | this message only posted: 2 Nov 2017 00:44
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Tony W
North Notts., United Kingdom

 

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Tim Lee wrote: Next Question ......
If we assume that for sidings etc at least, pre WWI turnouts were activated by an independent fixing of the point rodding to the nearest switch blade, can we assume that the rod itself would prevent the point blade rising or moving in relation to the stock rail (apart from laterally). 
If this is the case, and looking at the drawing which Martin posted earlier -

would it be right to assume that the extension shown on the right hand side of the drawing projecting through the stock rail, achieves the same thing on the side opposite to the actuation rod?

Edit - correction, looking again at the drawing it would appear that there is no extension through the stock rail - I assume therefore that the switchblade relies on the undercut of the planing to ensure against lift? Am I right in assuming that the extension is primarily used where the stock rail is joggled?
Hi Tim.
I think these stretcher rods are specials for Three throw blades only. See my pictures in message 13 where it is quite clear that the parallel extension is used to allow the stretcher rod to connect to the short inner blade (via the key hole slot) whilst passing through the hole in the longer outer blade without restricting its free movement.
Regards
Tony.

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55th message | this message only posted: 2 Nov 2017 08:30
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Tim Lee
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Tony W wrote:Hi Tim.
I think these stretcher rods are specials for Three throw blades only. See my pictures in message 13 where it is quite clear that the parallel extension is used to allow the stretcher rod to connect to the short inner blade (via the key hole slot) whilst passing through the hole in the longer outer blade without restricting its free movement.
Regards
Tony.
Of course .... now you say it that makes total sense.
Thanks

Tim

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56th message | this message only posted: 28 Nov 2017 07:31
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Tim Lee
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I hope some one can help. I have this detail from the trackwork at Monsal Dale station circa 1911. I am trying to work out what the mechanism is that I am looking at within the line of the outer rodding run just beyond the single slip rod and crank position?

Here is a somewhat grainy zoomed in detaiMight it be some form of compensator, or is it something to do with the single slip actuation? does anyone have a clearer picture of this type of mechanism?

When I look at the slip rodding what I think I see is the rod locating in the crank before you get to this mechanism and a rectangular bar of sorts connecting from the main rodding run to the crank in front of this - so on the face of it it seems that it is not part of the actuation?

Tim 

edit ... attached is the signal diagram and the picture from which the detail is taken.

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57th message | this message only posted: 28 Nov 2017 17:42
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Martin Wynne
West Of The Severn, United Kingdom



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Hi Tim,

If it's not a compensator, it is very difficult to imagine what else it might be. There were lots of patent designs for compensators and suchlike, here's a typical vertical compensator:



If it is a compensator, it will be roughly half-way between the signal box and the points (assuming no compensation is being done by cross-rods and cranks). The total rodding length in pull should match the total length in push.

regards,

Martin.

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58th message | this message only posted: 28 Nov 2017 20:32
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Tim Lee
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Martin Wynne wrote: Hi Tim,

If it's not a compensator, it is very difficult to imagine what else it might be. There were lots of patent designs for compensators and suchlike, here's a typical vertical compensator:



If it is a compensator, it will be roughly half-way between the signal box and the points (assuming no compensation is being done by cross-rods and cranks). The total rodding length in pull should match the total length in push.

regards,

Martin.
Thanks Martin,
I wonder if it is one of these vertical compensators ... just distorted by the foreshortening of the photo? The rods certainly appear to be swan necked down to fix as if the crank on the compensator is perpendicular ... looking at the drawing this would mean that the counter arm would not rise much above the horizontal which would also tie with the photo.

I shall go with this hypothesis unless something else presents itself.

Tim

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59th message | this message only posted: 28 Nov 2017 22:54
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Tony W
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Tim Lee wrote: I hope some one can help. I have this detail from the trackwork at Monsal Dale station circa 1911. I am trying to work out what the mechanism is that I am looking at within the line of the outer rodding run just beyond the single slip rod and crank position?

Here is a somewhat grainy zoomed in detaiMight it be some form of compensator, or is it something to do with the single slip actuation? does anyone have a clearer picture of this type of mechanism?

When I look at the slip rodding what I think I see is the rod locating in the crank before you get to this mechanism and a rectangular bar of sorts connecting from the main rodding run to the crank in front of this - so on the face of it it seems that it is not part of the actuation?

Tim 

edit ... attached is the signal diagram and the picture from which the detail is taken.
Hi Tim.
I think Martin is correct that what you are looking at in the rod to the left is a compensator, however I think it is for crossover 7 rather than 6. A crossover typically needs a compensator at the mid point in the rodding to reverse the travel of the two ends as well as between the box and the first set of blades if far enough away. The picture appears to be taken from the box. I think the compensator for 6 (in the other rod) would be somewhere near the second cover and thus hidden by the platform. I think it is possible to discern the fixing attachment under the rod to the right of the compensator in the blow up.
Tony.

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60th message | this message only posted: 29 Nov 2017 09:07
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Tim Lee
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Thanks Tony,

That makes sense. 

The compensator is interesting ... most of the pictures I have turned up for compensators on the Midland at this period are of the simple varietyAs Martin has suggested this appears to be the later but still vertical pattern. However it does appear to have a cover of sorts to the top and to vary in other ways from the diagram. I wonder if it was a Midland Prototype development and I wonder when it was introduced ... the photo is 1911 and my period is 1903, so it may be that I should model with the simpler form anyway. I have a question out with the Midland Railway study centre to see what they might have within the archive.

Regards

Tim

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Tony W
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Hi Tim.
The answer may be as simple as that basic type being incompatible with a cross crank at the same place. Special situations demand novel solutions.
Regards
Tony.

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62nd message | this message only posted: 1 Dec 2017 16:44
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Tim Lee
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Thought I would just upload some further research images of point rodding and rodding stools I have found as further reference info.













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