A Flexible Bridge for unloading / loading Locomotives

By David Watt, March 2010. e: dkwatt@nettel.net.nz

The difference in height between my vehicle and the unloading/loading ramp at our track is about 300mm. In attempting to transfer a locomotive between vehicle and ramp using the existing bridge piece was a positively dangerous procedure to both the locomotive and personnel.

A means had to be found to make this procedure much safer and simpler.

After giving the matter some thought, it was decided to make a bridge that could be pivoted at mid length. The bridge was made in two sections, each slightly longer than the locomotives, which can be quickly assembled ready for use.

The first components to be made were the turnbuckle assembly and the sockets. The shaft has 20mm diameter x 4mm lead trapezoidal form thread cut on each end, one left handed and one right handed. The nuts are made of cast iron, which fit into sockets made from short lengths of heavy steel pipe suitably modified. Short 10mm screws are fitted in both ends of each socket that can be screwed in by hand to engage in shallow holes in the ends of the nuts, preventing the turnbuckle from moving out of place while the bridge is being picked up and moved around. The rest of the bridge was built around the turnbuckle and sockets using 25 x 10mm, 10 x 10mm, 10mm dia. and 13 x 3mm steel stock. The bridge is designed to give a maximum angle of displacement of 20 degrees either side of straight, though it’s not likely to be used to this extent, but it’s there just in case. The two pivot pins are modified Allen head screws 10mm dia. and are placed in double shear, resulting in a stronger joint and eliminating eccentric loadings.

After completing the bridge it was tested at home for strength and ease of operation. One end was connected to a loco stand while the other was placed on strong wood boxes. Some wood blocks were placed under the centre portion of the bridge leaving a few millimetre clearance in case there was a failure. One loco was rolled onto the bridge and the turnbuckle turned a small amount in both directions, no problems were encountered. The second loco was then rolled onto the bridge with the first and the turnbuckle operated as before. There were no signs of failure observed anywhere. My calculations appear to have been about right. The next running day one loco and the bridge were taken to the track and the following pictures were taken.

	The two sections of the bridge and the turnbuckle ready for assembly.
	The bridge in position ready for rolling out the locomotive.
	The locomotive rolled out onto the first half of the bridge.
	The bridge straightened and the locomotive rolled onto the second half of the bridge.  Yes, the handbrake works well.
	The bridge has now been ‘bent’ the opposite way to allow the locomotive to be rolled off onto the track loading ramp.
	The locomotive rolled off the bridge onto the track ramp.
	View showing the large difference in height between the vehicle and the track ramp.

Overall, I’m very pleased with the results; the unloading/loading of locomotives can now be conducted easily and safely at our track or at any other track where the ramp facilities are of a similar construction.  While the bridge is ‘bent’ upwards, there is an increased possibility of tipping that need to be kept in mind during its use.  So long as the bridge ends are well supported and the rails kept level in the transverse direction there is no problem.

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