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Model Signal Engineering

For railway modellers to discuss and share ideas on realistic signalling arrangements.

Re: Model Signal Engineering

Unread postby Mike Hodgson » Mon Jan 28, 2013 10:33 am

Yes, signal location on a model does require careful thought. One one hand the location should be plausible in terms of sighting by the scale model's driver, but on the other it should be placed so as not to obscure physical access for uncoupling, re-railing etc. If it can be placed close to a high retaining wall or similar solid structure it is less likely to get caught on your sleeve etc. Tall signals are OK close to the backscene but a bad idea near an operating well or at the front of the layout where operators reach over.

And if you're going to the trouble of modelling it you want to be able to see it ! I am thinking here of a fully signalled 7mm layout with 3-link couplings and the main station has an overall roof. This roof hinges upwards from the back wall to enable access for coupling, and this is the only time you can see certain of the shunt signals! Also there are a few "signals" which would be required, but exist only on the "box diagram" as nobody would ever see them in their actual locations. On a lot of model railways, the distant signal should be off-scene roughly where the fiddle yard is!
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Re: Model Signal Engineering

Unread postby RichardH » Tue Jan 29, 2013 8:38 pm

davidwoodcock wrote:When I first noticed - in the 1960s - that SR rail-built signal posts didn't seem to have a classic bullhead rail profile, I started taking a closer interest. A rough survey of perhaps one hundred posts didn't find one with the classic profile, and none of those posts showed the signs of wear that one might expect had they been secondhand (or almost certainly third or fourth hand) double-headed rails, hence my suggestion that they had been rolled for the purpose. Photos which show the profile well are rare but, by chance, the front cover of the November 2012 issue of Backtrack has an excellent almost side on view of the up-from-Brading home at Smallbrook Junction in 1964; by comparison with numerous photos of bullhead rail in situ in the same issue, it will be seen that the profile was quite different.

Double-headed rails had become quite unfashionable a decade or so before the end of the Victorian era so any surviving into SR days would have been in sidings. The Southern initiated a programme of route upgrading to enable heavier locos to be used, so there would undoubtedly have been a cascade effect which would have rendered remaining d-h rail in sidings totally redundant. Certainly some of this ended up supporting signs and it may well have inspired the concept of the rail-built posts (ironically, perhaps triggered by the presence of the rail-built posts on the S&DJR), but I doubt whether much of it actually found its way into actual signal posts, other than perhaps the early "funnies".


Examining several bullhead examples on the Central Division dating from the 1930s/40s/50s, the rail was all quite noticeably worn and seemed to come in two or three different weights, one post was half 95lb and half 85lb? which is a bit thinner, and another one had the rail head surface profiled to a slight concave with distinctive burring at either edge.

The double-headed rail used in signal posts doesn’t look so worn but possibly if it fell out of favour on the main line only the best rails ended up in sidings for subsequent reuse - the couple of posts I have looked at both had LBSCR marked rail.

One final off-topic question – I have long wondered whether the posts were sent out ready made from a central depot or whether they were assembled locally from whatever spare rail was available at the time?
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Re: Model Signal Engineering

Unread postby South Western John » Mon Feb 4, 2013 10:50 pm

Mike Hodgson's reply of Monday January 28th helps me to polarise my thinking. For example, my proposed co-acting signal (scale 45ft post) will be close to the purlin in a corner of the layout where there is no coupling or uncoupling. Another junction signal will also be close to the opposite purlin, again in a far corner of the layout. The three signals that give me some concern are the down platform starter, a single doll on a Westinghouse 13 ft cantilevered gantry, while at the "UP" end of the station there are two bays each with 2-doll platform starter gantries. The further of these is at the platform end. One doll is to be the bay starter while the other is the UP through platform starter. The bay is for emu's that do not require any coupling or uncoupling. The other bay over on the DOWN side of the station (closer to the operator) also faces the UP direction and also has two dolls. One arm is for releasing reversing trains in the Down Main platform to the UP relief line while the other arm controls trains leaving this bay via the relief line to ultimately access the UP Main over a crossing and turnout.

I also note the remark about "the distant needing to be in the fiddle yard", but because I am working in OO gauge there is sufficient room to put a distant arm at a reasonable distance, certainly more than a train length from the Down Home gantry for the station.
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Re: Model Signal Engineering

Unread postby SimonC » Tue Feb 5, 2013 11:26 am

South Western John wrote:I also note the remark about "the distant needing to be in the fiddle yard", but because I am working in OO gauge there is sufficient room to put a distant arm at a reasonable distance, certainly more than a train length from the Down Home gantry for the station.

Reasonable for a model or reality? My understanding (and it's very, very limited compared to just about every other poster) is that about half a mile is a reasonable distance, depending upon all sorts of factors (line speed, gradients etc.), over 30' with OO. I suppose a good degree of compression of distance will be acceptable to some people and not others.
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Re: Model Signal Engineering

Unread postby Mike Hodgson » Tue Feb 5, 2013 12:43 pm

Line speed on a model merely means you have model signs with the cut-out figures, and the gradients may well be steeper than the Lickey. The gradients and curves are such that even if prototype stock could cope with them, the line speed would be extremely restricted. Compression of distance in models is a subject in its own right, as it is applied in a non-linear manner. It is interesting to see how the human eye accepts some things as looking right, and others as wrong. Unfortunately so many modellers don't model reality but rather what they've seen on other models. Of course, this is in part due to ignorance of the sheer complexity of signalling practice especially the more subtle niceties (and I'm no expert), so it is good that some modellers are using this forum to ask in an attempt to get it right.

If there's space to spare when the longest train is standing at the Home signal, it is just about plausible to model the Distant, provided that doesn't mean it is situated where a driver would have inadequate sighting from the tunnel/hole in the back scene; and perhaps the prototype would in any case have had an Outer Home there anyway (at least that's only 1/4 mile away with the distant a further 1/2 mile beyond that. Model rolling stock is typically full scale length although trains (especially goods) may well have fewer vehicles than they should; models of main lines rarely run 10-coach trains (say 200 yards long) in scales larger than N.

Platforms and sidings are shortened to just long enough to hold the longest train; they are also often reduced in number because baseboard space is at such a premium. However the distance between is stations is almost always massively compressed. This is one of the reasons why a speeded up clock is a good idea if you want to run to a timetable, and it also means any discussions about scale speed (=1/76 prototype speed ? Or compressed distance divided by accelerated time?) tend to be somewhat meaningless. Another example of the non-linearity is that you don't want to accelerate time very much when it comes to say the frequency of flashing the wig-wags at a level crossing. As for yodelarms or whistles, you would not want to reduce the audio wavelength by 1/76, but you certainly need to reduce the decibels!
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Re: Model Signal Engineering

Unread postby Signalhunter » Tue Feb 5, 2013 9:14 pm

To please ourselves (the builders), we intend putting a pair of LED's at both of the fiddle yard exits. These will display Y or G to replicate the Distant signal and will be worked from the (interlocked) lever frame. Thus, they will display the correct aspect to the (fictional) driver.
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Re: Model Signal Engineering

Unread postby South Western John » Tue May 28, 2013 1:27 pm

Having read the various letters on distance compression, it has left me very thoughtful and even more cautious. Too many signal arms imply chucking money about for no good reason. Perhaps it is better to err on the sparse side for more realism. The UP line on my layout emerges from a tunnel in which could be an imaginary and therefore unseen distant. The Home signal that follows guards a level crossing at the DOWN end of the through station platform. The platform starter then follows. At about a further 20 feet there is a junction signal with three dolls. The left hand doll is for a branch that disappears into a tunnel long enough to hide a 14xx 0-4-2T with autocoach but actually goes nowhere(!) - against a wall by the chimney breast - ! The double track mainline divides into four tracks signalled by the other two dolls on the junction signal. Both of these could carry a distant arm. On the DOWN side and approaching the junction where four tracks become two, will again be two junction brackets, the short left hand doll of each is for the bi-directional relief line into the downside bay and the goods yard. There could be distant arms on the taller of the two dolls. About 25 feet in advance of these junction signals are the home gantries for the through station. I am considering a short calling-on arm on the down main doll beneath the home arm. This is to enable a train to continue into the down through platform when beyond it the level crossing gates are closed.

As an aside to signalling matters, the blind tunnel will, of course require a liberal application of "No More Spiders" spray necessary in a loft to ensure that messy corpses do not get into the mechanisms of locos and there are no webs "stringing up" corners of the layout. I recommend the use of this spray to the modellers of all attic layouts. It does not harm spiders so please don't bother to report me to the RSPCA, but merely deters them - in fact I have not seen a single spider since using it up there.
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Re: Model Signal Engineering

Unread postby South Western John » Sun Mar 22, 2015 3:39 pm

I am now a little further down the road with point operation and signals. Model Signal Engineering for signals is very hard and time consuming. I am 77 y.o. and the sheer dexterity required to assemble the operating mechanisms on, for example, a Westinghouse 13 foot gantry have been quite taxing. I think that instead of attempting to solder the four rail rail-built post by soldering I am going to glue it at both ends. After the struggles with the operating system, it would be heart-breaking to damage the signal now that I have got so far. I have pre-drilled the lampman's platform to take hand rails but wonder if my low-level of dexterity will permit me to achieve the construction of these. I am hoping that the ladders won't be too hard.
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