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Mechanical Interlocking - How to learn the Lost Black Art?


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I don't wan't to digress further from the conversation about leverframes elsewhere in this subforum, where @micknich2003 has posted a wonderful mechanical interlocking setup:

 

I was wondering if there was a resource for us mere mortals to get to learn this? Certainly the heady heights of manual point actuation with manual interlocking is something I'd wished for as soon as I started to grasp the operational interest in proper signal obeyance on model layouts - but the prospect of translating a simple locks/releases table into a mechanical format completely eludes me.

 

I don't think I can be the only one who feels this way - nobody is born with an innate understanding of this stuff - but I don't really seem to know where to start to find out.

 

Any pointers for books, articles, etc. most gratefully taken!

Edited by Lacathedrale
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3 minutes ago, Lacathedrale said:

I don't wan't to digress further from the conversation about leverframes elsewhere in this subforum, where @micknich2003 has posted a wonderful mechanical interlocking setup:

 

I was wondering if there was a resource for us mere mortals to get to learn this? Certainly the heady heights of manual point actuation with manual interlocking is something I'd wished for as soon as I started to grasp the operational interest in proper signal obeyance on model layouts - but the prospect of translating a simple locks/releases table into a mechanical format completely eludes me.

 

I don't think I can be the only one who feels this way - nobody is born with an innate understanding of this stuff - but I don't really seem to know where to start to find out.

 

Any pointers for books, articles, etc. most gratefully taken!


See if blockpostsoftware.co.uk is of any help....

 

Phil

 

 

Edited by Phil Bullock
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The Kichenside & Williams book 'British Railway Signalling' has always been my 'go to' reference work for all aspects of signalling. It includes a simple example with explanation of how a locking frame is designed and works - the principles of which are just multiplied up for a larger installation.

 

I also have the Ian Allan ABC 'Signalling in the Age of Steam' by Michael Vanns. That also covers the subject and has a slightly more complex example with a tappet and locks diagram corresponding to a track diagram.

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Hi,

 

Last year I was trained in Mechanical Locking Design as the one of first group of ‘new’ mechanical designer for a quite a few years, and I thought that I would say that on the real railway there is no design handbook for Mechanical Locking.

 

Simply because the design of the locking wasn’t all that standard, there are guidelines yes, but it was mostly at the whim of the designer. There’s little chance that any lever frame is the same as any other lever frame!

 

So, don’t expect any resource to fully cover everything :)

 

Simon

Edited by St. Simon
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The plumpton interlocking shows round pegs with round holes - presumably so if there's space, any lever can displace a lock. In contrast, other designs I've seen have square or 45-degree corners to provide locking. Is there a meaningful difference?

 

image.png.3c0b7d66a6c20196c1afbc23a50a055f.png

(video above)

 

image.png.1c72c79d2dc5e056d9ec6f689b9a7744.png

GWR lock/tappets

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2 hours ago, LNER4479 said:

I don't believe so. Round pegs fixed into drilled holes in bars is easier / simpler to work with in model form (that's how the Modratec system works); the principles are just the same.

They are perfectly ok for basic locks and releases but they don't suit anything more complicated.  but then lots of people won't want anything more complicated.

 

However the mechanism is one thing and the rules of locking are another - and they come first.  The best basic source - if you can find a copy - is 'Principle of interlocking' No.2 in the old, long discontinued, series of IRSE hand books and the later, much larger and more expensive 'British Rau=ilway signalling Practice Interlocking Principles and Systems' also published by the IRSE.  Difficult to find either although specialist secondj hand booksellers may help - at a price.

 

There are four basic locks, viz:-

1.  One lever locking another when it is reversed,

2.  One lever releasing another when it is reversed,

3. One lever locking another in either position when it is reversed, and,

4. One lever lever locking or releasing another when a third lever is either normal or reversed. (i.e. conditional locking,  so called because the lock or release depends on the condition of a 3rd (or more) lever.

 

The basic locking principles really draw down from the Requirements (for Passenger Railways etc) although it no longer exists in its orignal form, and owe a lot to various 196 th century Acts of Parliament.  The Requirements can be summed up as follows -

A. It shall not be possible for a Signalman to clear at one and the same time any two fixred signals which may lead to a collision between two trains.  and that afterhaving cleared the signals to allow a train to pass he shall not be able to move any points connected with, or leading to, the line on which the train is moving until the signal is replaced.

B. Points also where necessary to be interlocked so as to avoid the risk of collision.

C. Levers operating stop signal which are next in advance of trailing points operated from the same signal box must, when reversed lock the points in either position (subjevt to a get out regarding making traffic working easier.

D. Distant signal levers must be so interlocked that the signals cannot give a clear indication when any of the relative stop signals is at danger.

 

From these worthy and wordy pronouncements of Govt we can draw up a far simpler list of basic interlocking rules -

i.   Stop signals must be interlocked with each other to ensure they do not allow conflicting movements.

ii.  Stop signals must be interlocked with points to ensure they they cannot be cleared unless points are correctly set (and conversely point levers set for a route which conflicts with any stop signal must lock that signal lever to ensure that the signal cannot be cleared.

iii.  Stop signal levers when reversed must lock in either position the lever(s) working all trailing points in rear of that signal.

iv. The lever operating a Distant signal should not be able to be moved unless the levers operating all stop signals applying to that line at that signal box have been reversed.

 

When we talk about stop signals this doesn't just mean semaphore (or colour light) running signals but also shunting signals such as ground discs and the various subsidiary signals.

 

In the real world what happens is that the track layout is drawn and then th signals are drawin in to provide the basic framework for numbering points and signals and from that detail something called a 'locking chart' or 'locking table' is prepared to show all the locks and releases etc.  different railway cmpany (and BR regions) had different conventions about the way in which they arranged the columns but basically there could be   columns for 'Locks', 'Releases',  'Locks In either Position', and 'Released By'  This link show an example of a GWR locking chart for Waltham Sidings Signal Box -

https://www.s-r-s.org.uk/html/gwa/S144-3.pdf

 

How you lay out your own chart or table is up to you but it's a step you can't really avoid - whatever sort of interlocking you are going to use.  For mechanical interlocking the arrangement of parts is drawn up in something called a 'dog chart' (the Western term for it, others might have had their own names).  yes, beware terminology did vary around the railway.

 

Now - if everyone is still here - we'll look at a very simple example.  A double line with a junction - very unusually having a single slip - to a single track branch line.  It includes Facng point Locks (A1 & A2) but we'll ignore them as we apply some of our locking rules.

 

Signal 2 and points A will lock each other because they conflict - A sets the route to the single line but 2 reads ahead on the main line.

But points A release signal 23 because it reads through A reverse towards the single line.

You might think that signals 2 & 23 lock each other because they are conflicting signals but there is no need for that because the lever working points A deals with it.  A however also locks signal 1 because they conflict with each other

You might think that signals 3 and 23 conflict but here again the point interlocking saves the day and does the job for us because point A reversed conflicts with the route set by point B reversed - so A & B lock each other.  And B releases Signal 3.

So what we have avoided is lots of direct interlocking between signal levers  because that locking is performed by the need for the point lever positions to lock conflicting signals and release those that they create a route for.

If there was signal at numbered line location No.4 it would lock points B in either position when its lever is reversed.  But in a heavily trafficked situation witha busy junction (which this one won't be) that lock might be omitted because it could also potentially lock points A if the lever working points B is standing reverse. 

388931948_sketch2.jpg.5f39e8f8b02db04e645ef619fafbc7dc.jpg

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Then when you have learnt all these basics, then you can start playing around with rotation locking, which in mechanical form is very hypnotic, or at least I found it so when I fitted it to my (full size) ground frame.... Then there is the addition of electrical locks as part of block working, AB or TCB.

Its all fun and interesting stuff, and its an alley which you can disappear for months, if not years.......

 

There is a book with DVD which I have on the bookshelf at home which allows you to build locking tables on the PC and will give you a design at the end of it. I wish I could remember the name of it, its got a red cover, and the title isn't obviously about locking.... and I'm stuck in work.

 

Andy G

 

 

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I believe I used the same excerpt of that book to do it! Its wonderful watching the tappets lift over the locks on the little ramps. I keep meaning to video it so that I can show people...

 

The locking fitters here in work didn't realise you could do it all mechanically...

 

Andy G

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I've come across one of those double thickness tappets as a friend has one, but we couldn't work out what it was used for, but now you have show one instance of its use, thanks.

The other drawings are interesting, but not really knowing what the lock shapes actually relate to makes them a bit more difficult to interpret. Fig 2 looks like it actually pushes the tappet sideways?

 

Every day is a school day when it comes to locking!

 

Andy G

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