Here we are … there is room, desire and time to continue the installation of the overhead line at the station. we start from the 1st track, the one furthest from layout edge, so that what is to be done is not an obstacle to subsequent processing. Here we didactically list the steps, in part already described here for the poles and here for the overhead portals.
This section of O.H.L. involves the use of M29B Italian Railways pole in addition to the portals already installed, two of which must be equipped with automatic tensioning devices. We then begin assembling the poles with brass tubes of decreasing diameters: 3, 2.5, 1.5 (the latter is a rod). Due to the tube thicknesses, these must be bored to insert them one another.
We assemble all the poles and begin to weld all the components: the various brackets and details are obtained from 0.3 and 0.2 mm photoengraving plates, as well as all the details of the automatic tensioning devices. Cntilever dropper and steady arms are made out of Sommerfeldt 0.4 mm. copper-plated steel, the steady arm brackets with square brass profile 1 x 1 mm, the fixing screws of the poles with 1,5 mm brass bar welded to the first section of the pole, while the insulators (in exact scale) are printed out of 3D prototyping resin.
The scaling of the tensioning devices has not been easy but, after the operational tests you can find here, we proceed quickly. The pulleys have great mechanical importance; these in fact must support and contain the 0.25 mm thick nylon wire which will be used to tension the catenary cables. The overhead line system to be reproduced is the one commonly called “1970”, with both wires under tension. Having found nothing in the market, we also made the 0.2 mm photoengraved pulleys. These are made up of 4 parts, two external ones with a larger diameter and two internal ones with a smaller diameter to hosts the nylon thread. Each part has a central hole; we insert the 4 parts in a brass microtube with external 0.6 external and 0.4 internal diameter . We hold the parts togheter and weld. The welds must then be cleaned and filed.
The poles are now ready for painting. The moving parts will not be painted, but burnished.
We mask the parts not to be painted and apply a Tamiya grey base coat. The final painting is obtained with an airbrush aluminum effect paint. Once the masks have been removed, the poles will be adequately weathered with specific products.
Our catenary should be tensioned and operating. To make this possible, after several attempts, here is the illuminating idea, which came by chance trying to tune a Celtic harp. What could be simpler and more effective than guitar machine heads. These have implicitly locked position, thanks to the gear / worm couple, they are robust and easy to apply. We find low-cost heads on eBay (Fender marked…maybe…), we 3D print supports and that’s it.
Each automatic tensioning device will have a double tensioner (for wires) and a single one (for the pole forestay ). The fixed tensioning poles will have only the single tensioner. The sub-board installation is simple, once the holes for the tension wires and the forestay have been drilled. Once the correct inclination has been calculated, the central position is sighted with a harmonic steel wire passing through (from the top of the pole to the return of the tensioner). The final part of the forestay and the one wrapped in the guitar machine head are 0.2 mm phosphor bronze wire …yes…the same used for guitar strings, what better match then! We insert a compensation spring and put in partial tension while waiting for the catenary.
We place all single pseudo-winches for the affected catenary line. We will position the double winches together with the contact wire and the catenary wire. In the figure a pole ready to receive its catenary.
We start installing all the poles. We drill the through holes, insert the plinth and level the pole by inserting, if necessary, 0.3 mm brass plates to compensate for any inclination.
The foundation plinths for the tensioning poles are drilled for the nylon wire slides down to the tensioner sub-board. We therefore drill the block and board and insert brass tubes into the holes to ease the wires sliding.
We then install the pole by connecting the forestay and moving parts to the tensioners. The operation is a bit complicated because the nylon thread tends to come out of the pulleys, but with a little patience we can stretch everything.
Now let’s weld the wires. These will be cut at the junction of the layout panels; so we weld the them starting from opposite sides to rejoin the center. At the end of the work we tension the contact wire. We position the catenary wire in the same way, taking care to leave it slightly taut. This in fact will have to arch in the middle of each span.
Once wires have been fixed, we weld the droppers. It is a long and tedious, but not complicated work. In the end, a veil of dark paint will enhance the finesse of our catenary. Our “Caimano” engine performs the test, during which we have the opportunity to correct small imperfections. The test confirms our calculations were correct for the catenary alignment.
The short video below shows the system operating… let’s roll with raised pantographs… as to the truth !!
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