Blog- Clachbeg: trackwork - Laying the mine spur turnout

RSS Fetcher · May 2, 2014

After completing the station entrance turnout, next up is the extremely sharp turnout to the mine spur.

The mine spur actually pre-dates the station: it is the last remaining section of the ½-mile standalone track constructed of portable rail panels when the mine was first opened, along which a Highland pony named Blackie drew a single skip to carry the high-grade ore to an old iron furnace for smelting. That endeavour was unsuccessful and most of the track was taken up and reused, but the last few panels were left in situ and connected to the new branch line at Clachbeg. (Re-cycled 12 lb-yd rails can be found on the stonemason and goods spurs as well as on the tiny turntable at Clachbeg.)

The minimum radius for the Clachbeg branch is half a chain, however the 1:3 curved left-hand mine spur turnout uses that for the outer road, and the inner, diverging road is laid to a radius of just 12'3", which was the ruling radius of the portable track system. The mine spur has an axle-load limit of 1½ tonnes and only lightweight internal-combusion locomotives may traverse it with a single skip; it sees a couple of traffic movements a week.

The turnout is on the same template as the station entrance turnout, and is constructed in the same manner. The main challenge is the tightness of the curves and thus the dramatic angles involved. This shows the marking-out of the inner stock rail.

The full set of rails laid out on the template. The inner loop is at 33' radius, the turnout at 12'3" radius... The main road is straight through the crossing vee, and the switch rails are straight; the diverging road is curved through the crossing vee. By eye, against the template, everything looks ok to within half a millimetre.

Close-up of the central ironwork. The crossing vee is not very pretty but works fine, and will be blackened and rusted.

A new approach to the inner fishplates using brass channel: like the original this holds the square-headed bolts from turning, making the fitting of the nuts easier. Beside the inside fishplate is an outside one for comparison. The inside fishplate measures 30 mm and is made of 2.5 × 1 mm channel with an inside width of 1.7 mm.

Slightly blurry closeup of the fitted channel fishplate: one bolt turned a little but held. Pleased with this!

Double-checking with lots of track gauges: even in this scale things can get cramped.

The completed turnout. The tight radius of the diverging road made this very tricky, as the flanges of wheels rub inside and out against the rails and check rails. A number of tests with my little wagon and some Sierra Valley wheel sets led to much fettling of the diverging road check rail as well as the inside of the wingrail. Mounting the switchstand was quick and easy; its throw is adjustable, so I was able to adapt it quickly to the throw (I had drilled the holes in the stretcher bar a scale inch too close together).

View along the main road of the turnout with the station entrance turnout in the background.

Detail of the crossing vee and the diverging check rail and wingrail. To prevent the flanges from binding I resorted to using my Proxxon drill with a sanding disk to sand the faces of the check rail and wing rail; I then burnished the sanded areas with a wire brush to achieve a silky smoothness again. This tiny adjustment made all the difference, and the wheels glide through the sharp curve now. I also filed and burnished the nose of the crossing vee.

Although not a turnout, the first piece of the outer loop is on the same template, and after the two turnouts this was a doodle to make. This picture shows the two rail lengths after bending to size. As the rail bender cannot bend the last couple of centimetres of rail, I bend the whole rail length and then trim off both ends to fit.

Drilling the 1.5 mm holes in the rail ends. I mark the distance from the rail end using a micrometer, which is enough to scratch a mark against the web of the rail to show where the hole should be; all the rest is by eye.

A view through my magnifying lamp showing the fiddly fishing together of the rails. The hexagonal nut I am about to fit sits inside the brass nut spinner held between thumb and forefinger, while I press the bolt head to prevent it from dropping out when I hold the nut against it. With practice this is quick, and satisfying. I tighten the nuts very gently, such that once locked (by tinning the bolt three with solder prior to shortening the bolts) the fishplates remain a slightly loose fit against the rails.

The completed template; it's about a metre wide.

A test fit of the template onto the baseboard led to some minor fettling of the edges to get the rails to line up. This template also sees the start of the rising gradient to the branch line and the falling gradient to the mine, so it will have to be heavily weighted when glued in place to ensure that it flexes as desired. The 3 mm MDF is ideal for this.

Checking the branch line end of the template before glueing in place. These rails will require fishing together in situ, which will be rather more fiddly than at the workbench.

The connection to the mine spur includes a change from 25lb/yd rail to 12lb/yd rail (Code 205 to Code 148), which will need special fishplates. The rail ends will need to be tweaked a little to achieve the fit, but once fished together this will not be noticeable. With hindsight—hmmm—I should have left the mine spur template loose until it was connected to the next one, however this is no big issue. As long as each template is accurate to within a millimetre then all is well.

The template with the entrance turnout and the mine turnout, glued in place on the baseboard. This shows the effect of the diverging gradients, adding a sense of vertical dimension.

A trackside view showing the mine spur dropping away to the left and the branch line climbing in the distance. I still have to fish the rails together to join this template to the mine spur and the branch line.

Finally, a view up the branch line showing the start of the ascent in the middle of the crossover between the turnouts. I hope that Works Engineer John Hurt is content with progress so far...

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