Sunday 27 March 2016

Thakeham comes out to play

Thakeham will be at the Wealden Railway Group exhibition next Saturday 2nd April, in Steyning. So I've retrieved it from the loft and removed it's cover to check it out. A bit of dusting and a vacuum was in order - some sawdust from fitting the cover mostly - and in some places the printed paper block-work has bubbled, but it's minimal and not normally noticeable.


I've applied a fresh rubbing of graphite to the rails and test run, which revealed a mystery short circuit when the points were thrown. After some investigation it was found to be a point blade that had shifted along to touch the frog rail - this is a problem as the blade is electrically connected to the stock rail and the frog is switched. Forcing a blade into the gap shifted it back, I'm still thinking of a more permanent solution.


That aside running was smooth and problem free. I will need the super-glue to a couple of details that have fallen off though. However while it was out I took the opportunity to take some photos on my new camera, using a tripod and playing with the manual settings. I'm rather pleased with how they have come out.


I've been asked to provide some information about the prototype and the model, and exhibition organiser Andrew Knights shared some photos he'd taken of the railway shortly before it closed, so I put together a display using them along with photos I'd taken of the locos now at Amberley, the site today, and the model under construction. The board is simply two cork-boards attached with a pair of small hinges I'd put together some time ago for something my wife was involved in - I knew it would come in useful again!


If you get along to the show do say Hi...

Saturday 19 March 2016

Using Map Data

Recently a work discussion about getting map data - in that case the altitudes for a route - resulted in a colleague pointing me at this website:
It didn't take me ling to think of non-work uses too. As a teenager I doodled many track plans, and often schemed out "might-have-been" railways on Ordnance Survey maps. I'd attempt to check contour lines crossed against distance to ensure they weren't implausibly steep, but it wasn't reliable and as I was often planning Narrow Gauge lines through hilly landscapes the gradients would have been pretty severe.

So I plotted one of my favourite schemes using the website, clicking points onto the map, the "Terrain" view gives contours which help. The string of co-ordinates produced can be copied from the box below the map which I pasted into a text file, then imported into Excel. Plotting the latitude and longitude and placing a map picture behind the plot is a quick way of drawing the route - the Excel plot can be stretched either way so I made sure the two end points were correctly positioned on the map, the rest will then be correct. Click the images to enlarge them.

That's rather fun but the data allows much more analysis - easy enough in excel, even if it is rather like the day-job! This site gives the formula for distance between co-ordinates, so of course gradient can be determined (change in height over distance). However for that I used an adjusted altitude - representing the track height after civil engineering - and calculated the deviation of that from the ground, i.e. the magnitude of the earth-works. The gradient can often be eased by increasing the height of embankments and cuttings, but for a Narrow Gauge line the balance would be in favour of less costly earth moving and more gradient. It's worth bearing in mind that a delta of a couple of meters can be regarded as negligible, and since my route is often running along the side of a slope, it only represents a few meters deviation of route - or of inaccuracy of my mouse-click on the map! I did go back and adjust some points to get a better route.

So here's my analysis. This line does have severe gradients - 1 in 44 for a sustained period, with another at 1 in 37 at it's worst - but these are not unusual for NG lines (the Welshpool and Llanfair has a section at 1 in 29) and are a good excuse for short trains! That does mean the earthworks are minimal, though an embankment or viaduct up to 25 ft (8m) tall is required to cross a valley just beyond Scorriton, and a 25 ft (8m) deep cutting is needed at Holne - both are plausible for this kind of line. A bridge across the West Dart is also needed near the end of the line, but at a point were that would be relatively easy.

This plot shows the altitude of the line (black) with the terrain (green), and also the gradient as a percentage (so 1% = 1 in 100, 3% = 1 in 33).

So I have a plausible route for an imaginary line, and I'll tell you about it's history another time!