Monthly Archives: April 2013
No, this is not the end. It is not even the beginning of the end. But it is, perhaps, the end of the beginning. Interlocked Lever Frame – Part 4
With thanks to someone else for the quote.
I managed to get all of the locking bars, installed over the weekend and the dogs (the teeth that engage in the sliding bars) to get the interlocking going. And this is what I get to:
This shows all of the components assembled in place. The dogs engage in slots in the sliding bars but the dogs have angled sides – so if nothing holds them in place the movement of the slider pushes them to one side and the slider can move. When another slider is in the way (ie there is an opposing lock set) then this can not occur – so it locks shut.
To stop the sliders popping up when they encounter a lock, a lid has been fashioned. I wanted all of the locking to remain visible, so this is just a skeleton.
I did find that the angles of the slots needed to be just over 45 degrees for the locking bar to move easily and they also need to match the dogs quite neatly. If I do this for real, I think some lost wax masters and then castings will be required to ease the process of manufacture.
The frame does lock well and neatly. Of course I made a few errors in where slots were to go but having made it from plastic, these were actually quite easy to sort out. What is more significant is that there is some slop in the levers – this occurs worst where the yoke of the bar that runs through to operate the toggle switch and sliding bars goes over the base of the lever. The hole in this is a bit too big and it means that the lever can move 30 % of its intended movement before it makes the sliding bar move and hence encounter the lock. This does slightly defeat the object of the locking and will need some work. I have an idea of linking the two more physically but if this does not work, then it may be back to the drawing board.
All in all, it works though and it is quite fun working through the desired move, working out what then needs to be thrown and in what order – although this may send my team a bit over the edge in the heat of an exhibition! However, some manufacturing refinement is going to be needed to make it work better. I remain tempted to use the potential kit that might be available but this makes the locking invisible and I am not so certain about this. Food for thought!
The saga continues and I have now made all the trays and the bars that the locks go into. As I have yet to colour the actual levers on the frame, I have coloured these to ease my understanding of things.
As this is an experiment, I am making this out of plasticard/evergreen strip to speed construction. The final thing will be in soldered and milled brass. I have yet to come up with a plate to secure all these bars in place, so they will not flop out as they presently appear that they might. This is what we currently looks like:
I have been warned that I may snap my tappets from the locking bars or something else. This is due to the significant mechanical advantage that the lever has over the through of the bar – if you look at the end view you can see that it is about 10:1, so I can see why I am being warned. Ultimately this is an experiment so I will take it easy with the frame if it breaks I will know that it will need to be tougher next time!
The bridge is coming along and is now close to finished (constructionally).
It has taken a lot of time with plastic filler to get the stones to meet neatly at the corners and also to be coursed sensibly at the corners. Having said this, I am inclined to think it is one of the more important parts of modeling structures and buildings. Cracks or missing sides/ends on a building are just a total no no and even an untrained eye (I am a chartered surveyor so it is worse for me!) spots the error immediately.
This is where we have got too:
I am not happy with the string course at the moment, it sticks out too abruptly and possibly the same for the copings to the top of the parapet – so more filing and sanding………….
However, it does look like a bridge and I doubt the civils guys will condemn it!
The bridge is in fact modelled on the one at Killiecrankie, but there were very similar ones at The Mound, Kyle of Lochalsh, Keith amongst others. Heres a picture of the Kyle one:
The advantage of using the Killiecrankie bridge is that I had previously modelled one for a layout of this station and whilst the abutments are still firmly attached to some mothballed boards, the deck could be reused. The deck has a nice skew to it to make it a bit more interesting and utilises lattice girders; which few seem to bother modelling. This is what it looks like:
In terms of abutments, most Highland (and indeed this is common to most scottish lines) had bridges with curved wingwalls swept back from the face of the abutment. To give the layout some locational character, this was something I wished to produce. This is where we are at presently with the abutments:Typically, the random or dressed stone ranges from Wills are my favoured mediums but seeing Andy G making a good go utilising Slaters 7mm coursed stone I thought I would have an experiement with this. This is because many of the later bridges on the Highland used the same coarsely dressed stone; like this one at Dalwhinnie:
And these show the bridge deck on the abutments as they stand:
_________________ Mark Tatlow