Signal consruction info

[Ruston]

Evening all,

I am building a Saxby & Farmer lower quadrant signal. This is the first signal I have ever built, so I need some help.

I'm not sure where to put the wire from the weighted arm to the signal arm itself. I assume the weight (not yet fitted) is there to pull the signal arm into the danger position if the cable from the signalbox breaks? If that's correct then I would need to put the wire to the LH hole? I tried this but it doesn't look right and the end of the weighted arm clashes with the end of the signal arm when "off". I don't know if the weighted arm should be lower but I put it there because there was an indentation in the cast post. The parts are all from MSE and there is no overall instructions on how to put a complete signal together with any of the parts.

[Ruston]

I'm surprised that no one can help with this.

[meil]

18 hours ago, Ruston said:

Evening all,

I am building a Saxby & Farmer lower quadrant signal. This is the first signal I have ever built, so I need some help.

I'm not sure where to put the wire from the weighted arm to the signal arm itself. I assume the weight (not yet fitted) is there to pull the signal arm into the danger position if the cable from the signalbox breaks? If that's correct then I would need to put the wire to the LH hole? I tried this but it doesn't look right and the end of the weighted arm clashes with the end of the signal arm when "off". I don't know if the weighted arm should be lower but I put it there because there was an indentation in the cast post. The parts are all from MSE and there is no overall instructions on how to put a complete signal together with any of the parts.

No the weight is there to tension the signal wire. You have the lever in the wrong way round.

[Gordon A]

My understanding that the weight was to return the signal to danger should the wire break or be broken - fail safe.

I have seen tensioning devices in a signal box for signals a fair distance away.

Gordon A

[Ark Royal]

Hi Ruston,

 

Whilst no expert in semaphore signals other than having built some (not saxby & farmer), i'm willing to assist

 

I concur with Gordon that my understanding is the purpose of the weight is to return the signal to danger if a break in the input cable should occur and assist when the input cable tension is released during normal operation of the signal box lever to allow the signal arm to return under gravity assisted by the lever arm weight.

 

Tensioning of the input cable is undertaken by compensator bellcranks along the run of the cable back to the signal box. The output drive would actually be an adjustable fork ended rod to set the correct length.

 

In the picture you posted , the weighted lever is at its lowest position and thus the signal must be at "Danger". You are correct in saying that the output drive wire from the lever to the signal needs to go in the LH hole of the lever, as per the drawing below

 

 

 

Here is evidence that this was common practice,  Greenford Lower Quadrant - You Tube

 

This the only set up that would achieve lower quadrant workings. If the output drive rod was swapped to the input cable hole then as the lever was raised the output rod would move downwards toward the post bottom and that would make the signal arm move upwards.

 

The issue of the lever arm hitting the signal arm when in the "Clear" position, i would assume, is due to the lever arm assembly being too close to the signal arm. The dimple in the post may well just be a sprue mark. So the lever assembly can be moved further down the post. Remember there is likely to be a bellcrank or pulley at the base of the signal post for the input cable to change the run direction. There seems to be no mention of any set distance the lever has to be from the base of the post and again i am only assuming that local features will dictate the actual position.

 

I have also seen pictures in "A Pictorial Record of Southern Signals Illustrated edition by G.A. Pryer (ISBN: 9780902888814) " that show that the lever assembly has been offset from the post centreline. (In the above picture towards the semaphore signal lenses side". This would help offset the severity of the joggle in the output drive rod as would lowering the positon of the lever assembly.

 

 

Hope this helps.

Happy Building

 

Mark 

 

 

 

[Ark Royal]

Heres a lower quadrant from Eridge which shows the position of the lever compared to the post 

 

[Nick Holliday]

There are some things about the construction of the model  that are clouding the issue. First of all, the normal pivot of the signal arm was by means of a casting on the arm side of the post, as can be seen at the Bluebell, if you scroll down this page

http://www.bluebell-railway-museum.co.uk/accessions.htm

This means that the hole where the actuating rod fits is roughly in the centre of the post.

Secondly, the hole for the actuating rod on the operating lever should, normally, be closer to the centre pivot.

This means that the offset between the rod's pivot at arm and lever is only a couple of inches, and any joggle at the lever end would be minimal, and probably achieved by a short vertical section above the lever, or merely lost over the height of the post.

This also means that the location of the balance weight is not critical, and it can be positioned as best suits the location, especially on platforms, normally on the arm side of the post, but not necessarily. It also should be noted that there wasn't always an actual weight. In many cases the weight of the lever, spectacle casting and the actuating rod would have been sufficient, on their own, to return the arm to danger if the wire were to break.

[TheSignalEngineer]

The Bluebell one looks a bit of an artist's impression to me. For a real S&F in the wild try the one at the bottom of this page. https://signalbox.org/gallery/s/mitcham.php

 

You will see the arm pivot actually appears to be in the centre of the post and the operating rod running down the R/H side of the post to the weight bar. This is probably one of the last S&F ones to survive, not being replaced until the late 1970s.

[Nick Holliday]

Not sure what is meant by artist's impression, but another Bluebell signal can be seen here

https://www.shutterstock.com/image-photo/sheffield-park-east-sussexuk-november-22-343295591?src=ezKPByCm2Arr6tRab3Y_nw-1-87 which has the same detail.  The one in signal box.org is a lattice one, and the design is obviously different, as it was for many of the other lattice signals on that website , although the lattice posted signals on the Southern often appear to have a similar bracket on the arm side of the post. It just goes to show that there is no absolute answer.

[t-b-g]

Any signal, upper or lower quadrant, was designed to return to danger if the operating linkage broke. It could break between the balance weight and the arm, so each arm was balanced in a way that it would return to danger by itself.

 

In a lower quadrant, the heavy casting of the spectacle would be much heavier than the thin timber or metal arm. In an upper quadrant, the arm pivot is positioned in such a way that gravity would return the arm to danger.

 

If a signal was very close to a signal box, with a really short wire, it could appear without a balance weight. If the balance weight was there to return the signal to danger, surely all signals would have them, irrespective of the distance from the box.

 

So although a balance weight might look as if it is here to return the arm to danger and would help add to the gravity acting on the arm, its main function is to keep the wire between the lever and the signal taught.

[Ruston]

Sorry for not replying etc. but this new-fangled forum means that I can't keep track of when anyone's replied to something, so I didn't know until I just happened upon this thread again.

I swapped the arm around to the other side. I found some photos on google, which showed some with the weight on the same side as the signal and some on the opposite side, so I guess there isn't a right and a wrong way around but the way I now have it set up looks better as it avoids the arm clashing with the weight.

[TheSignalEngineer]

On 05/02/2019 at 18:03, Nick Holliday said:

Not sure what is meant by artist's impression, ................................

Never take what you see in a museum or presevation site as how the real thing was, unless they have a picture of it in situ and operational. I remember back in the 1960s a museum curator saying he had never seen a signal with a piece of ironwork like one on my grandfather's district. My grandfather came clean and said he would never see another one as the timber was giving way  and the signal only had a few months to go so he reinforced it with a wrought iron cistern bracket he found in a disused toilet block in the goods yard.

[Nick Holliday]

1 hour ago, TheSignalEngineer said:

Never take what you see in a museum or presevation site as how the real thing was, unless they have a picture of it in situ and operational. I remember back in the 1960s a museum curator saying he had never seen a signal with a piece of ironwork like one on my grandfather's district. My grandfather came clean and said he would never see another one as the timber was giving way  and the signal only had a few months to go so he reinforced it with a wrought iron cistern bracket he found in a disused toilet block in the goods yard.

I only used the "museum" photo because it was the only one I could find on the internet which showed an LBSCR signal, a company that had a long association with Saxby & Famer.  Before using it I made sure that it was representative of actual LBSC signals and matched the drawing and photos in Southern Signals.

Just to demonstrate what the real thing looked like I found this on my hard drive:

Just to add to the mix, this signal would appear to have the lever arm mounted on the side of the post, parallel with the tracks, you can just make out the operating rod cranking over and then running up just inside the edge of the post.

[TheSignalEngineer]

Nice example to show both the side spindle casting variety and the mounting of the balance lever low down on the side of the post away from the track.