Scatchbuilding 'suspended' catenary

[ash39]

Hi all,

 

I'm working on a 00 layout which is split over three boards, I'm tackling one board at a time and the first one is just straight track and no pointwork so should be a good starting point for building catenary.

 

This board is the station, so rather than individual masts I want to suspend it , as per this photo of Leeds station:

 

 

333014 & 91109 by Flash_3939, on Flickr

 

I'm not sure if there's a correct term for this type of installation - feel free to correct me if so.

 

I'm thinking of using brass H-section for the masts, connected directly to the baseboard through the platforms (I will then build the platform tops around them), but I'm not sure how to build the assembly between the masts. Will I be able to build something tough enough to withstand contact from potentially two pantographs at once as trains pass?

 

I know guitar string is often used for the live wire itself, what thickness do people recommend? Would this be strong enough to use for the rest of the assembly?

 

Thanks

Ash

 

[Edwin_m]

The construction where the contact wires are hung from cross-wires is known as a headspan.  This was the standard method for sections with three or more tracks on all electrification schemes since the 70s (northern WCML, entire ECML, Colchester-Norwich, Stortford-Lynn, London-Bedford etc) though there were some sections where rigid gantries were used for various reasons.  However a "dewirement'" of a pantograph under headspans will bring down a lot of wires, so the electrification schemes currently in progress will not use them (though I saw some on the Reading topic, but I think these were low-speed wires in the depot). 

 

No doubt others will be along to advise on the best way of modelling it! 

[ash39]

Thanks Ben, I have heard the term headspan so I should have known that.

 

Yes, where I live near York most of the ECML is 4-track and is wired in this way. This part of my layout will be tricky enough to wire for me as a newbie, but the junction on the next board with crossovers and sidings is 4 tracks wide at one point and will cause me a few headscratching moments I think!

[RBE]

Head spans should work ok provided that you get tension in the wire between the uprights, you see a lot of this style of catenary modelled but let down by the headspan wires waving around and thus not looking as is there are under tension. I would solder wire loops around the H uprights first and then carefully make hooked versions of the headspans from guitar string where the hooked ends are a fraction shorter than the distance you have to span, you can then stretch them across between the uprights. The issue that you will get though is when the temperature varies as the headspan will expand and contract although to a very small degree over that length. You could try to source small stiff springs that resemble insulators and use those at the ends of the headspan wire to give flexible tensioning which would be much better. I will need to do the same when I get around to modelling Neale Bank as there will be headspans on there. Its a very long way off yet though.

 

Cav

[Dagworth]

Headspans are easily modelled, I have them on Dagworth. http://www.flickr.com/photos/dagworth/8104080173/sizes/o/in/set-72157631808842648/

 

The upright columns are not vertical, they lean out very slightly, and then the tension of the headpsan wires tries to bring them back to upright. This deals with the expansion problem.

 

My uprights are two lengths of C channel soldered back to back to make the H section, then guitar string for the cross wires. I drill holes through the soldered join between the C channel sections and mount the three wires on one upright before planting. The other upright will have the holes drilled before planting but the wires not soldered in until the uprights are fixed in place and the glue has gone off. Once everything is set then the cross wires are passed through the second upright and then heated enough to melt the solder and fix them in place. As the wire cools it will contract and give the needed tension.

 

The apparatus suspended from the headspans is scratchbuilt from brass rod, I use lengths of single strand tinned copper wire stripped from 7/0.2 layout wire to tie it all together then solder it once its all tied up.

 

Hope that helps

 

Andi

[ash39]

Thanks for the replies, I think I'm almost there now in terms of knowing what I'm doing.

 

 

I think rather than soldering the C section back to back and drilling through, I'll go with H section and use loops to hold the wires as Cav suggested. The reason being some of the masts will be lampposts/roof supports. I can then build the whole lot the same way.

 

One more thing, I've got 2m of track to do for this first board, will 6 masts 333mm apart be OK or would 7 masts 285mm apart be better? I'm thinking the first would look more prototypical but the latter would be stronger and more robust.

[Dagworth]

Real ones are spaced at about three coach lengths apart, on plain straight track I tend to stretch them to about 600mm apart, still closer than scale but far enough apart to give plenty of space and access. On curves and pointwork the spacing will be determined by the track requirements.

 

Andi

[ash39]

Really? Will the wire still be strong enough at that distance?

 

Maybe 4 @ 500mm apart or 5 @ 400mm apart would be more suitable for mine then. I'll have to mock something up with card and see how it falls.

[Dagworth]

I've had not trouble at all with 600 mm spans of Catenary, the important thing is that the supports are strong enough to withstand the needed tension on it, the tension is sufficient to keep it true, and that the pantograph springs are seriously weakened. My pans are set such that a pencil rested on the head will press the pan down.

Guitar string is my wire of choice, it is designed to be tensioned and belted hard. I've proved that numerous times at shows by giving the overhead on Dagworth a fairly substantial twang, get the tension right and it becomes quite musical!

 

Andi

[Clive Mortimore]

Real ones are spaced at about three coach lengths apart, on plain straight track I tend to stretch them to about 600mm apart, still closer than scale but far enough apart to give plenty of space and access. On curves and pointwork the spacing will be determined by the track requirements.

 

Andi

 

 

Hi Andi and all

 

Redrawn from a BR drawing.

[Clive Mortimore]

Thanks for the replies, I think I'm almost there now in terms of knowing what I'm doing.

 

 

I think rather than soldering the C section back to back and drilling through, I'll go with H section and use loops to hold the wires as Cav suggested. The reason being some of the masts will be lampposts/roof supports. I can then build the whole lot the same way.

 

One more thing, I've got 2m of track to do for this first board, will 6 masts 333mm apart be OK or would 7 masts 285mm apart be better? I'm thinking the first would look more prototypical but the latter would be stronger and more robust.

 

Hi Ash

 

I need to double check but I am sure I have read that OLE mast are not to be used as lamp post as well. The reason being should there be an inuslator problem and the 25KVa earths that is where it goes not down the wires of the 240v system.

[ash39]

Hi Clive,

 

Sorry yes I should have been clearer on that. I didn't actually mean lampposts, I meant structural elements of the station. Ie at Leeds, (although the above picture doesn't show it) a lot of the knitting is bound to the roof supports.

 

I will be having a section of overall roof, around 1m long, so I'll probably end up with 2-3 'standard' headspans with H-beams, and two incorporated into the roof building and attached to the roof supports.

 

I'll probably make a start on it this weekend. My soldering isn't the best but there's only one way to get better!

[ash39]

I said I know what I'm doing but actually I don't!

 

A few specific questions if anyone can help?

 

* How do you secure the masts to the baseboard? I was thinking of soldering the H-section onto a piece of flat drilled brass and then bolting/gluing to the board?

 

* How do you connect the actual 'live' wire to the span, and add tension to it?

 

* How would I create a hook to join the cross span wires to the masts? I'm guessing guitar string isn't solderable.

 

Thanks everyone

[Dagworth]

My masts are fixed by drilling a hole through the 9mm plywood baseboard that is slightly smaller than the mast. The base of the mast is sharpened to a point with a file and then hammered into place. Once planted like this they are pretty solid, but I then put blu-tac around the mast below the board, and fill the hole around the mast with ballast before flooding with dilute PVA. Once that sets very little will shift them.

 

The contact wire is mounted onto the registration arms attached to the diagonal rods of the equipment hung on the headspan, the wires are attached by bending the end of the wires into small hooks that clip around the registration arm. I have put stuff up on RMweb about this before, there is some stuff in my Ravensclyffe thread here http://www.rmweb.co.uk/community/index.php?/topic/3288-ravensclyffe/?hl=registration&do=findComment&comment=23810

Tension mechs are either springs mounted off stage in fiddle yards or under bridges (easy) or by miniature versions of the real thing (very hard!)

 

Guitar string solders very well!

 

Andi 

[ash39]

Thanks Andi, I'll have a good read through that thread before I start, looks useful.

 

The tension thing, I have a tunnel to the fiddle yard at at one end, but the other end joins onto the next bit of track with no scenic break. Does it only require tension at one end? And I'm sorry to sound even more simple, but what is the spring assembly like? I'm struggling to get my head around that bit. The tension mechanism in the video looks superb but certainly way beyond my ability at the moment, this is very much a learning process! Maybe when I build something in future I'll progress to that.

[Dagworth]

I've got some photos somewhere of the tensioning mech hidden under the bridge on Dagworth, I'll try to find them and put them up later.

 

Andi

[Gordon H]

Thanks Andi, I'll have a good read through that thread before I start, looks useful.

 

The tension thing, I have a tunnel to the fiddle yard at at one end, but the other end joins onto the next bit of track with no scenic break. Does it only require tension at one end? And I'm sorry to sound even more simple, but what is the spring assembly like? I'm struggling to get my head around that bit. The tension mechanism in the video looks superb but certainly way beyond my ability at the moment, this is very much a learning process! Maybe when I build something in future I'll progress to that.

 

Tensioning at one end is usually safer.

If you have a spring at both ends, the wires have to be free to move in both directions. Then if a wire breaks somewhere in the middle, both ends suffer as the springs pull all the intervening masts and registers apart in opposite directions.

With a single spring, only one end up to the failure point will see this effect.

[ash39]

I'm still stuck at the 'working it out in my head' stage, I think I need to buy a small amount of bits and have a go at putting something together. Sometimes you have to learn from cocking it up!

 

I'm confident at soldering now, I'm sure by the time I've built a few masts it might even be neat. I just need to work out how it all goes together, particularly the contact wire. I don't understand how it's connected to the arms.