Chairs, Keys and long walks!

[SHMD]

I have a question regarding the “direction” of which way the Keys were knocked into Chairs to hold the Bullhead rail in place.

Often, you would see keys not knocked in all the way. They were sometimes too big to drive fully home. It is this that I am queering.

 

Were the Keys knocked in, on both rails, from the same direction?

OR was one rail knocked in from one direction and the other rail knocked in from the other direction?

 

I am wondering because if the Keys were knocked in from different directions then when the line was 'walked' to check the way, the 'Platelayer' would be moving/walking in the direction of the Keys on one side and, when he walked back, would be automatically moving in the direction of the keys on the other side?

 

Were single lines treated differently from double track lines?

Did it not matter are track panels were all 'made' the same?

Did the 'way' change all the time?

Was there regional differences?

…

 

 

Thanks,

Kev.

(The things that sometimes drive us to distraction...........)

 

[SHMD]

I forgot to add the photos...

 

 

 

 

Kev.

 

[peter220950]

As I understand it there's a natural tendency for the movement of traffic to affect things, as a loco moves forwards it tends to tighten keys into the chair in the direction of travel (I think).

 

Thus for a double track they tend to all be the same way, on both rails, but different directions for the two tracks. Single lines are random but around 50/50 mix to equalise the tendency for rails to loosen the keys and 'walk' And possibly also affected by inclines where rail will tend to slide down the hill, aided by the loads imposed by locomotives trying to gain traction or brake, so there would be a need to bias the quantities away from 50/50 mix on single lines..

 

But I could be wrong, often I learn stuff from dodgy rail forums (Fora?) and I wouldn't always believe what people tell you.  

 

I hope it's right, otherwise there's an awful lot of Exactoscale chairs on my layout that are going to need re-fixing - (my main lines are all the same direction and the single lines are random.)

 

Peter

[martin_wynne]

Hi Kev,

 

It is important to prevent the rail creeping through the chairs, because it causes the essential expansion gap at the rail joint to close up. There is then a risk that the rail will buckle when it expands in hot weather.

 

The general creep of rails is in the same direction as the direction of traffic. On double track the tapered chair keys are therefore driven into the chairs in this direction, and any rail creep will tend to tighten them in the chairs. Note that this means the direction in which the keys are driven (hammered) into the chair. The result is that the thick end of the key remains protruding from the chair pointing in the opposite direction.

The reason the rails move in the direction of travel is because of the way the rails flex under load and get pushed forward by the wheels. It is similar to what happens when rolling pastry -- the whole mass moves forward on the board in the direction in which it is being rolled.

However, there are sometimes situations where rails are found to move backwards -- for example on the inside rail of sharp curves and on steep rising gradients. If a situation is found where the keys frequently work loose, some or all of them will be turned round and driven in the opposite direction.

On single lines or where traffic is bi-directional, the usual rule of thumb is to drive the keys "towards the joint, towards the station, towards the river". That means on level track between stations the keys are driven into the chairs towards the nearer of the two rail joints in each rail length. Approaching a station, where trains are braking or accelerating, most keys are driven towards the station. On steep gradients, most keys are driven downhill.

 

But on any track, on the chairs immediately adjacent to a fishplate at a rail joint, the keys are driven in towards the fishplate, because it is physically impossible to fit them the other way. 

Just to repeat, the thick end of the key remains protruding from the chair in the opposite direction to the direction in which the key is driven into it -- this can lead to confusion in describing the hand of model chairs with moulded keys.

regards,

Martin.

[philsandy]

Yes as Peter has described.

 

According to Iain Rice in his book on track building the keys are driven home in the same direction as the traffic would travel.

On single lines, keys are driven in one way, and on the next chair along, the opposite way.

[SHMD]

A great big thank you to you two gents.

 

Wow, so much more to think about.

It makes so much more sense when it is explained.

 

I think i'll just knock 'em all in in roughly the same way!

 

 

Kev.

[SHMD]

...I'd better taper my keys now...

[jim.snowdon]

...I'd better taper my keys now...

Well, in general, no, but since you are modelling GWR track, yes.

 

To quote from W.H.Cole* in 1928, "The key is usually straight, with uniform section, but the G.W.Railway uses a tapered key, 7" long, 2 3/16" at the driving end, and 2 3/32" at the other."

 

So, your keys should be tapered, but I very much doubt that you could actually detect a taper of 3/32" in 7" when modelled in 7mm/ft scale.

 

Ultimately, keys were driven in the direction that the local ganger knew was best for not falling out under traffic, and the amount by which they were driven into the chair depended on the tolerances of the chair casting and the key. Being wood, their dimensions would vary over time and with the weather, so some would end up driven right through, whilst others might be only half way through the chair jaws.

 

* Permanent-way Material, Plate-laying, and Points and Crossings, auth. W.H.Cole, Indian State Railways. I have the ninth edition, dated 1928 - the first edition was dated 1885.

 

Jim