robmcg Posted December 2, 2012 Share Posted December 2, 2012 Sorry to ask a dumb question but were the wedges in the chairs of bullhead rail generally to the left or the right on British track, or was it random? I have assembled my C&L code 75 rail with the wedges on the left, looking at the track from outside the line, but it doesn't always look correct. Rob Link to post Share on other sites More sharing options...
micknich2003 Posted December 2, 2012 Share Posted December 2, 2012 Keys are driven into the chairs in the direction of traffic, that is apart from the joint sleepers where the fishplates make it necessary to drive in the keys from the opposite direction. Mick. Link to post Share on other sites More sharing options...
Talltim Posted December 2, 2012 Share Posted December 2, 2012 Mick is generally correct, but it is a little more complicated. If you can imagine a train powering along the track, the rail will try to slide through the chairs in the opposite direction to the train. Thus having the chairs as mick says the rail attempting to move will drive the wedges (keys) in tighter. However in a situation where trains are normally braking, the force will be in the other direction do the keys will need to be in the other side. Obviously on bidirectional track it's not a simple to work out, but on a hill for example, going up the train will generally be under power and down be braking. I suspect, with the local track gangs of the past, any strange anomalies where it would seem sensible to have a key on one side but it kept working loose would be picked up on and corrected. Link to post Share on other sites More sharing options...
micknich2003 Posted December 2, 2012 Share Posted December 2, 2012 Mick is generally correct, but it is a little more complicated. If you can imagine a train powering along the track, the rail will try to slide through the chairs in the opposite direction to the train. Thus having the chairs as mick says the rail attempting to move will drive the wedges (keys) in tighter. However in a situation where trains are normally braking, the force will be in the other direction do the keys will need to be in the other side. Obviously on bidirectional track it's not a simple to work out, but on a hill for example, going up the train will generally be under power and down be braking. I suspect, with the local track gangs of the past, any strange anomalies where it would seem sensible to have a key on one side but it kept working loose would be picked up on and corrected. Thanks for your more in depth reply, I'm aware of what you said, I purposly kept it simple, as you say Single/Bidirectional lines can be complex. Best Wishes, Mick. Link to post Share on other sites More sharing options...
robmcg Posted December 2, 2012 Author Share Posted December 2, 2012 Thankyou for those logical replies, I am very relieved that the 'left hand side' wedged track is not redundant! And it explains why I had not picked up a sense of 'right' or 'left' being normal in photos. Thanks again for taking time to answer. Rob Link to post Share on other sites More sharing options...
Southernman46 Posted December 2, 2012 Share Posted December 2, 2012 The standard for Bi-Di is for the keys to be driven in opposite to the direction of the primary traffic direction - where there is similar flow in both - they are driven altenately. Rule of thumb - local situation can change this. [Edit - left out key (no pun intended) words that altered meaning] Link to post Share on other sites More sharing options...
robmcg Posted December 3, 2012 Author Share Posted December 3, 2012 I presume that braking and gradient would alter this on both single bi-directional lines and double track lines, I must look at photos more carefully! Link to post Share on other sites More sharing options...
RMweb Gold martin_wynne Posted December 3, 2012 RMweb Gold Share Posted December 3, 2012 If you can imagine a train powering along the track, the rail will try to slide through the chairs in the opposite direction to the train. This is not correct. The general creep of rails is in the same direction as the direction of travel. The tapered chair keys are therefore driven in to the chairs in this direction, and any rail creep therefore tightens 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 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. It is important to prevent rail creep, 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. 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. 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 model chairs with moulded keys. regards, Martin. Link to post Share on other sites More sharing options...
Talltim Posted December 3, 2012 Share Posted December 3, 2012 ^ What Martin said! Sorry for getting it the wrong way round Link to post Share on other sites More sharing options...
robmcg Posted December 3, 2012 Author Share Posted December 3, 2012 >> the thick end of the key remains protruding in the opposite direction.<< (to the direction of travel) I will use this as a default, with yard, gradient and junction variations to the other way around suit special circumstances... in other words, excusing errors on my part! Thanks all. Rob Link to post Share on other sites More sharing options...
The Evil Bus Driver Posted December 5, 2012 Share Posted December 5, 2012 This is not correct. The general creep of rails is in the same direction as the direction of travel. The tapered chair keys are therefore driven in to the chairs in this direction, and any rail creep therefore tightens 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 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. It is important to prevent rail creep, 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. 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. 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 model chairs with moulded keys. regards, Martin. That would be one hell of a tin of biscuits... But yeah, it makes perfect sense. Link to post Share on other sites More sharing options...
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