Bridging the gap

I fancied a change from the soldering and wire, so today I began to look at the curved river bridge on the station approach. In any case, this will need to be broadly in place before track laying can proceed across it. The prototype is situated on the outskirts of Tulle and crosses both a road and the Corrèze river. In my case, the redesign has meant that the original bridge has become two, slightly diverging and on opposing gradients of about 1 in 55, with the rear one falling.

I cut the track beds from 3mm MDF and stiffened them with a rib laid longitudinally. Quite a lot of time was spent considering the alignment of the river and road, in particular the river as I want it to look more significant than a trickle, and the Correze is around 70 feet wide at this point. Another critical point was to get the geometry of the arches right, so as to retain the correct appearance.

I did this by taking a reasonably square screen shot from Google Earth street view, backed up with dimensions from the same source. I edited the picture in Irfanview, then pasted it into PowerPoint. This allowed me to resize the image to the dimensions of the model. I then inserted a shape over the picture and adjusted the shape so that it lay over the photo. This meant that the arches would be symmetrical and smoothly-curved. I then cut out the shapes with a Stanley blade and used the holes created as a template for cutting the bridge faces from 1.5mm thick artist’s mounting board. This was glued with PVA in place, thus securing the track bed. I used a box-form of spacers to keep the sizes vertical.

I had reservations about placing two bridges so close together like this, but I think it is going to work. The next problem will be how to make the lower track disappear into the tunnel without resorting to unrealistically steep hillsides..

Texte française sous les photos…

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J’ai voulu faire quelquechose de different du soudre et de l’alimentation. Donc j’ai commencé aujourd’hui à considérer le pont en courbe à l’approche ferroviaire de la gare. En tout cas, il faudra l’avoir en place avant que je puisse mettre les voies là-dessus.

Le pont original se trouve aux environs de Tulle, et traverse d’une route et de la Corrèze. Sur le réseau, il y en aura deux, sur des rampes opposées de pente 1,5cm/m.

J’ai découpé du médium 3mm pour les plateaux, renforcés sur le dessous. J’ai passé beaucoup de temps en considérant les dimensions et la configuration, surtout de la fleuve qui a environ 20m de largeur à cet endoit. Je voulais retenir la taille du pont, donc j’ai pris ses dimensions sur Google Earth. Puis j’ai fait un «screenshot» et l’a édité dans Irfanview. Je l’ai mis en PowerPoint en ajoutant le grandeur à cel du modèle. Puis j’ai utilisé des circles pour créer des arches symmétriques et je les ai découpées. Ҫa m’a donné un patron pour le découpage des quatre faces en carton de montage d’un epaisseur de 1,5mm.

J’ai collé les quatres en place avec de la colle blanche.

Je ne le croyais pas que les deux ponts si proches iraient bien, mais je crois que ҫa va. La prochaine problème sera le disparaison de la voie inférieure en tunnel sans besoin d’une colline d’une pente non réaliste…

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