Minimum distance between Common Crossing and next Switchblade

[Dungrange]

Hopefully this is an easy question: is there a minimum distance between the V of a common crossing and the switch of the next turnout?

 

I want to have two turnouts one after the other, the first is right hand and the second a left hand turnout, but I want to construct these as close together as possible without actually constructing a three way / tandem arrangement.

[martin_wynne]

Hopefully this is an easy question: is there a minimum distance between the V of a common crossing and the switch of the next turnout?

 

Hi David,

 

The minimum is that the switch tips must clear the end of the wing rail and check rail. It also requires a special order from the design office, of course.

 

See: http://85a.co.uk/forum/view_topic.php?id=2506&forum_id=11

 

See under the leading tender wheel:

 

From this topic: http://www.rmweb.co.uk/community/index.php?/topic/18451-peterborough-north/page-248&do=findComment&comment=1549853

 

And:

 

linked from: http://s49.photobucket.com/user/TrogUK/media/Toe%20and%20crossing.jpg.html

 

regards,

 

Martin.

[Dungrange]

Okay, to answer my own question, I found that current Network Rail guidance (page 99) states that 

 

The minimum opening between running edges is to be:

• 1067 mm for point motor worked switches; and
• 385 mm for Rail Clamp Point Lock (RCPL) operated switches.

It therefore looks like it is the space to the side, that matters more than the in-line length.

[TheSignalEngineer]

The dimension for clamp locks is important as they have to bolt to the outside of the stock rail. For point machines that is the current standard for fitting a machine directly to the soleplate as close as possible to the points. There are many historic instances, some still existing at Birmingham New Street, where it is impossible to fit clamp locks to the rail  or machines directly adjacent so the points are worked by motors fixed to extended soleplates beyond the next track.

[martin_wynne]

Okay, to answer my own question, I found that current Network Rail guidance

 

Hi David,

 

Many thanks for finding that link. As far as I know the handbook hasn't been generally available outside the rail industry. I have posted the link on Templot Club as it obviously has wider interest than this specific topic.

 

Thanks again,

 

Martin.

[dhjgreen]

I am concerned about the copyright statement on the front cover, do not get into trouble.

[The Stationmaster]

I am concerned about the copyright statement on the front cover, do not get into trouble.

 

The link to it is in the public domain and is not restricted by any need to sign-in as a registered user.  A large amount of railway industry documentation has to be readily accessible for a variety of reasons and is therefore in the public domain but you will find that certain documents (for very good reason) are only available to registered users; you'll soon find out whether or not you're allowed to look at them when you link to one (unless you happen to be a registered user of course - but then you have to sign-in).

[Dungrange]

I am concerned about the copyright statement on the front cover, do not get into trouble.

 

David,

 

I never actually read the copyright statement, but I don't work in the rail industry.  It is a Network Rail document, published by Network Rail on their website and is therefore already in the public domain.  That said, looking at the URL, it seems to be published on a relatively obscure part of the Network Rail website which could make it difficult to find.  I only stumbled across it from a Google search.  I doubt that quoting a sentence from this document would constitute reproducing it and nor do I think providing a link to Network Rail's own website would be considered as disclosure to third parties without their knowledge.  Anyone on this forum could stumble across this document as I did.  I therefore don't anticipate getting into trouble, but thanks for the concern.

 

Hi David,

 

Many thanks for finding that link. As far as I know the handbook hasn't been generally available outside the rail industry. I have posted the link on Templot Club as it obviously has wider interest than this specific topic.

 

Thanks again,

 

Martin.

 

Martin,

 

That's fine - perhaps Network Rail's move from private sector to public sector changes what is deemed worthy of publication under, for example, Freedom of Information Legislation.  I hadn't realised that this information was once restricted knowledge and people like yourself may not have seen what is in it.  It doesn't really cover the bullhead era as all of the data relates to flat bottom rail, but there did appear to be a lot of information for those who are interested in many technical details and mathematical formula.

 

As long as I can build a few model railway turnouts in 4-SF that look reasonably realistic, that's where my devotion to the subject ends.

[dhjgreen]

OK good that it in the public domain. Everone on here seems to be very careful about copyright and correctly so, thank you for letting me know.

[martin_wynne]

I hadn't realised that this information was once restricted knowledge and people like yourself may not have seen what is in it.

 

Hi David,

 

I do have a printed copy (of an earlier version), but unfortunately I have never been able to post extracts from it or provide links.

 

Now that you have found it on Network Rail's own web site, everyone can read it.

 

It is 6 years old, and there are later versions, so I suspect it has been lurking there on the server forgotten for some time.

 

For bullhead details it is much better to refer to the various editions of the BRT handbook from the PWI, and of course David Smith's book on GWR track.

 

regards,

 

Martin.

[Dungrange]

The dimension for clamp locks is important as they have to bolt to the outside of the stock rail. For point machines that is the current standard for fitting a machine directly to the soleplate as close as possible to the points. There are many historic instances, some still existing at Birmingham New Street, where it is impossible to fit clamp locks to the rail  or machines directly adjacent so the points are worked by motors fixed to extended soleplates beyond the next track.

 

I have a follow on question: what exactly is a Rail Clamp Point Lock (RCPL)?  I found the following Railtrack Clamp Lock Handbook from 2003, but I'm still not sure that I actually understand what these are for.  Do these actually move the switchblades (ie they are a form of point motor) or are they simply a locking mechanism that also requires a mechanical means of actually moving the stretcher bar and the RCPL simply stops the blades moving under traffic?

 

Colin Craig seems to produce the necessary cast white metal details, but I'm not sure what else I need to complete the detailing.  It seems that I can fit a RCPL to all turnouts, but don't have the space to fit one of the larger point motors without a little redesign.

[Grovenor]

but I'm still not sure that I actually understand what these are for.  Do these actually move the switchblades (ie they are a form of point motor) or are they simply a locking mechanism

They do move the switchblades and are a form of point motor. The complete unit has the pair of clamp locks, one for each switchblade that contain the moving, locking and detecting parts and a electrically hydraulic pump unit that provides the motive force via a pair of hydraulic cylinders connected to the clamp locks. The handbook you found will explain the details.

The pump unit connects to the clamp locks with a pair of hoses so can be anywhere in the vicinity. I don't know if Colin does a casting of the pump unit.

Regards

[Dungrange]

Thanks Keith, that's actually what I thought but the presence of what appears to be mechanical linkages made me wonder if I was misunderstanding.  However, I have since noticed that 'beast66606' posted some pictures on an earlier thread on RMWeb, which shows that these mechanical linkages only connect with another stretcher bar in the same turnout.  That is, there is only one set of clamp locks, but both stretcher bars need to move together (assuming the turnout has more than one set of stretcher bars).

 

The photograph at the bottom of this page on the Colin Craig website indicates that he does indeed do a casting of the pump unit, which is a little box sitting remote from the turnout.  The description states "CC20T 

Sprue of castings for cosmetic clamp lock – (Actuator cylinder assembly), two rail mounted clamp lock boxes, and control box".  That seems to be the pump unit, the two 'motor' units (yellow boxes) that are attached to the outside of the stock rails and I assume that the actuator cylinder assembly is the 'bar' running between the two switchblades.  It looks like I need to send an order to Colin, but thankfully don't need to redesign my track plan to fit point motors into the plan.

 

Life was much easier in the days when I thought that a Peco point would do.

[TheSignalEngineer]

What date is the layout set, as there may be some subtle differences in the clamp lock equipment. They did change occasionally, especially in the early days.

[Dungrange]

What date is the layout set, as there may be some subtle differences in the clamp lock equipment. They did change occasionally, especially in the early days.

 

My model time period is circa 2007, but the track work (or most of of it) is still going to be bullhead rail (because it is easier to build). I'm assuming that it was laid some 20 to 25 years earlier and is about to be replaced.

 

The 'story' is that what was once a secondary through route was truncated in the Beeching Era to become a terminus served by DMUs, the station goods yard was subsequently closed in the 1970s (to become a car park / development land) and some rationalisation of the track work took place thereafter.  This would most likely have resulted in the closure of the signal box, a switch from semaphore to colour light signalling and track renewal would probably have taken place at this time (say early 1980s).  This would mean that the turnouts would most likely no longer be operated by mechanical means, but by some form of point motor or RCPL which I will need to replicate.  The subsequent decades saw relatively light traffic levels, but by the early 21st Century there has been significant growth in demand requiring an increase in service frequency, the facility to operate longer 6-car units on the line and the track work is life expired.  As such a re-modelling contract has been signed to rip all of the track work up and relay with new flat bottom point work and concrete sleepers and extend the platforms to accommodate longer units.  This allows me to bring an overgrown Engineers siding, which has seen little use in the past back into operation with material deliveries and gives me an excuse to run some on-track plant such as a Tamper (which can sit parked in the bay platform).

 

Therefore, although the stock operating on the layout will be from the post-privatisation era, the track work should probably relate largely to the BR era of the 1980s as may have been applied to a lightly trafficked branch line (although I'm happy to have some more modern replacement equipment depending on what details are actually available).  That also means that some details could be from a different time period if they are subject to replacement due to failure.

 

All I really want to avoid is something that simply looks wrong to anyone with any knowledge of the subject.  I can happily live with the 'wrong' version of particular equipment, but not glaring omissions that I suddenly find I can't retrofit.  I therefore want to make sure that I can fit all of the necessary S&C apparatus before I start building the track work (which is something I have never done before). 

[Mike152]

A bit of a newby question maybe, but if you want to move the switchblade closer to the common crossing, how do you get Templot to do this?

[phil-b259]

Thanks Keith, that's actually what I thought but the presence of what appears to be mechanical linkages made me wonder if I was misunderstanding.  However, I have since noticed that 'beast66606' posted some pictures on an earlier thread on RMWeb, which shows that these mechanical linkages only connect with another stretcher bar in the same turnout.  That is, there is only one set of clamp locks, but both stretcher bars need to move together (assuming the turnout has more than one set of stretcher bars).

 

 

 

What you are describing is called a 'Backdrive'. Its purpose is to ensure the switch fits snugly against the stock rail at the rear of the point (The gradual increase in stiffness of the switch rail as the plaining reduces and the cross section increases means the mechanism at the tips struggles to move the switch fully across at the rear) AND ensures that an adequate gap* is maintained on the open side to prevent wheel flanges from rubbing against or striking the open switch rail - (the later being a key reason why the stretchers at Grayrigg went and failed with disastrous results).

 

* Known as the "Free Wheel Clearance"

 

Backdrives can be fitted to RCPL, point machines and mechanical points - usually anything grater than a C switch has them and in the case of longer switches you can get two backdrives added thus holding the switch rail tight in 3 places. The most common type is constructed with cranks and channel rodding and is placed on the outside of the rails - except on the Southern region and other places where conductor rails are fitted  and it thus has to be placed in the 4ft. Other designs are in evidence in some places however, including the 'torsion tube' design, commonly found with HPSS point machine setups.

 

Also its worth noting the number of stretcher bars varies depending on the length of switch and are independent of the backdrive in the sense that a C sized switch may have a single backdrive connected to stretchers 1 & 4 with stretchers 2 & 3 merely connecting the two switch rails together. Stretcher bars come in 3 main types:-

 

 'Fixed stretcher bars' - steel strips (painted yellow or black) which require the techs to drill holes in the long end once on site and at a distance to ensure compliance with the FWC standard and which require replacement if the FWC requires adjusting. these are the traditional type of stretcher whose design hasn't changed much in the past hundred years.

 

'Green Adjustable Stretcher bars' - Green painted square section rodding with threaded ends and nuts so as to allow adjustment mounting brackets - and thus the FWC.

 

'Tubular Stretchers bars' A large round white tube and different coloured motion units (depending on the rail type) which can again be adjusted to maintain the required FWC

[Dungrange]

A bit of a newby question maybe, but if you want to move the switchblade closer to the common crossing, how do you get Templot to do this?

 

I'm probably not the best person to answer as I am still getting used to Templot.  However, effectively with the peg at the toe end, you want to reduce the length of the first turnout, which will allow you to start the toe of the next turnout closer to the crossing of the first turnout.  Alternatively, you can set a blanking length on the second turnout to remove the first couple of timbers.  You'll need to do both if you want effectively no space between turnouts as per the photographs that Martin posted at the start of the thread.

 

In the end, I decided against squeezing the two turnouts too close together and stuck with the standard spacing.  The reason for this was that if the crossing V and switch stock rails are delivered to site pre-machined, then either one of these would have to be shortened on site, or specially made to a reduced length or as a combined unit, which would of course make it more expensive.  Therefore whilst there are clearly examples as evidenced by Martin, I figure that such shortening of the distance between turnouts would only occur in practice if there was good justification for doing so.  A little tweaking of the alignment allowed me to push these a bit further apart than i originally thought i needed.

[martin_wynne]

A bit of a newby question maybe, but if you want to move the switchblade closer to the common crossing, how do you get Templot to do this?

 

Hi Mike,

 

I have made a new Templot video showing how to get a switch close behind a V-crossing, see this topic: http://85a.co.uk/forum/view_topic.php?id=2928&forum_id=1

 

If you restart Templot you can watch the video from the help > watch a video > switch close behind V-crossing menu item.

 

Or if that doesn't work, download it to watch in the Templot video player from:

 

 http://templot.com/fbr/switch_close_behind_V-crossing___1.fbr

 

It is 26MB, so will take a few seconds to download.

 

If you don't have Templot and prefer to watch it online, or on a mobile device, it is also on this web link (in poorer image quality):

 

 https://flashbackconnect.com/Default.aspx?id=BDXvSdUuD-vmjFK4us4vxA2

 

regards,

 

Martin.

[Mike152]

Thanks Martin, the video was very useful and the commentary was an added bonus.

Mike