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Wagon Loading Gauge

DocRef: JC6a

Not an item seen often on the modern railway, except perhaps on preservation sites, is the wagon loading gauge.

In these days of almost universal containerisation, where the load is either of fixed dimensions and travelling on standardised wagons or is a "block" train of purpose built vehicles, such as tankers conveying liquid or pulverised material, it not necessary to check that a load is "within gauge", so it will not foul bridges, tunnels or lineside structures.

In the days when every station had its own goods yard, or just a single siding, a multitude of loads of varying shapes and sizes would be loaded onto open wagons and sheeted over with tarpaulins. Before travelling out onto the mainline, they would have to safely pass under the loading gauge.

The design for each railway was very similar and would consist of a free-to-swing arc hanging from a post or gantry arrangement built either of old rails, timber or reinforced concrete. The arc shape would vary between railway companies to reflect the different standards to which the lines had been built in Victorian times. Some arcs had adjustable segments to cater for more than one profile, where the train was to travel over a route involving the tracks of more than one company.

Below I will describe the construction of a rail-built common GWR-design.

This is quite a simple project, based up a drawing from "A Pictorial Record of Great Western Architecture" by Adrian Vaughan, and consists of just eight major components plus the detailing.

To make a start you will need two lengths of Code 250 bullhead rail, yard lengths are available from Cliff Barker. One 273mm in length, the other 236mm long plus a 215mm length of 1/8 inch diameter brass tube or rod.

Solder together the two lengths of rail, edge to edge, having aligned one end of each to coincide at one end of the combined unit. You will need either a high-power, 80 Watts minimum, soldering iron or a butane torch to produce sufficient heat.

When this has cooled, measure 230mm from the base, being the end where the joined rails form the base, and use the mark to drill a 1/8 inch hole through the webs of the combined rails.

Take the tube or rod and make a mark 42mm from one end. The tube should then be passed through the hole in the rails, starting from the side with the longer rail length, until the mark just touches the outside web of the rail. If you have done this correctly, you will have 42mm of the tube projecting from the post on the side with the longer rail section.

Now carefully "square up" the tube to the rail in both planes. When satisfied, solder the tube to the rail. You have now completed the most difficult part of the job!

Next job is to fabricate and attach the bracing. This consists of two short sections of brass strip forming the triangulation strut and tie on the shorter section of the tubular arm, plus two supporting ties spanning the longer section.

Cut two lengths of 3/32in x 1/32 in brass, each 60 mm in length and fold at 5mm from each end, such that the folded sections form a 135 degree angle.

When the strut and tie are held against the rail post and cross tube, an isosceles triangle is formed with 45 degree angles where they meet post and cross tube. Mark and then solder the strut and tie, first to the web of the rail and, having checked the angles, then solder to the tube.

The ties supporting the cross tube are two lengths of 60 thou. inch brass wire, one 80mm and the other 160mm. Measuring from the web of the post make marks at 70mm and 150mm along the cross tube. Placing the end of each section of wire on these marks, then bend the final 5mm of the opposite ends of each so that they align with the web of the rail, pointing towards the top of the post. When you are satisfied, solder to the post and cross tube.

You now have just the small details to add for which you will require some brass strip, I used 3/32 inch x 1/64 inch, plus some fine brass wire or chain.

Firstly produce a "binding loop" around each of the ties where they are soldered to the cross tube and solder in place. Next with the post to the left, then make marks on the cross tube at 36mm, 75mm, 98mm, 123mm and 161mm from the web of the post rail.

Again with the post to the left, next go to the marks at 75mm and 123mm and make the supports for the chain from which the gauge bar arc will be suspended. Fold around the tube and close, by pinching, the loop, being sure to leave at least 5mm projecting below the tube, and solder so that the mark you have made aligns at the left edge of the loop. Drill to accept a 1/32 brass rivet, which will be used to attach either a chain or hanging hook.

The remaining three marks are to position open-ended loops, which retain the wheels/guides for the cable which operate the "arc". Again leave a few mm below the cross tube to attach parts and align with the mark to the left of the fixing.

There are just three stages now :

1) A wire "hook" is positioned approx. 60mm from the base of the post, which retains the wire cable on the real thing, a piece of 40 thou. inch wire soldered to the rail web will suffice.

2) Another "pulley wheel" clamp, just below where the post meets the cross tube, again folded from brass strip and soldered to the web of the post rail.

3) The actual "arc" which constitutes the "gauge".

The pulley wheels are represented by sections cut from plastic tube which are glued into their mountings after all soldering has been completed. The operating cable is made from thick button thread, stretched taut, glued to the pulley wheels and knotted through holes in the suspended arms of the gauge bars.

How you produce the arc of the gauge bars will depend on whether you will be using it in the garden or indoors and whether you will fix it "rigid" or wish it to "swing".

If free to "swing" you won't want it blowing to and fro in the breeze, so it needs to be heavy (thick brass or cast metal) but if "rigid" or indoors, then a lighter solution, plastic card, is a possibility.

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Page last modified on February 27, 2018, at 10:44 PM