I am not sure when the Whitton truss bridge across the Murrumbidgee River at Wagga had its overhead arch girders replaced with steel beams, but it was before 1970. And I do not know the reason, as the double track Whitton arch bridge at Albury over the Murray River still has its arches
|Shortly after being built in 1879, this NSW Archives picture shows the Wagga Wagga bridge, and the timber trestle|
In any case, I needed to model the Murrumbidgee bridge as it appeared in 1970, and that meant scratch building the overhead “U” support beams. The first part of the Murrumbidgee bridge blog post is way back on the 26th June, 2017. I finished that blog post saying that I was waiting for ABS styrene from China, or a source of brass “C” channel or the correct size.
|The bridge as it appeared in my June 2017 blog.|
To cut a long story short, the styrene “C” channels from China were substandard, and I was unable to locate the correctly sized brass “C” channel. However, I don’t like to leave projects sitting around for too long, and I wanted a distraction from the pain of shingles (yeah, that is another story), so a start was made.
The styrene “C” channels, whilst poor, could be modified. I cut out 7.5 cm sections that were more or less straight from the 50cm lengths supplied; and reduced the height down to approx 1.5mm. These I put into a jig to hold them at the correct distance apart, whist I glued the styrene spacer plates on. Unfortunately, removal of the jig stressed the joints out, and the whole lot disintegrated. Better to find that out now, than after I had spent any more time on them.
|The failed girder attempt with styrene|
As no suitable brass “C’ channels were available. I had little choice than to fabricate my own from strip brass. In this case I was very lucky. I had in my supply of North Yard brass strip, enough 1.5 x 0.25 x 150mm, and 3.0 x 0.25 x 150mm strip pieces to fabricate the 3.15 metres of the “C” channels of the correct size for the bridge. Yes, that is a lot of brass strip
|Parts needed to make one 150mm strip. This completed strip will be cut into two 7.5cm sections. This is a fortunate measurement, as it eliminates waste of the brass.|
Once the “C Channels” were made, I fitted them into the distinctive “U” shape of the prototype, and matched a pair back to back, and soldered spacers to hold them a scale foot apart.
|Three 7.5cm sections make one half of the "U" beam|
|One completed "U" beam. The spacer plates are 3mm strip brass.|
All these measurements have been guesstimated from the prototype photos I took during the bridge replacement over a decade ago
|After being gas axed, the bridge truss sections were craned to one side awaiting removal. This view shows the interior construction of the girder quite well.|
To match the prototype, I will have to fabricate 7 “U” beam supports, 4 on the first girder, and 3 on the second.
“U” beams were secured to the bridge using triangle gusset shapes. These were made from sheet brass, but soldered to the bridge with 144 degree C solder, rather than the 60/40 solder I had used earlier. I did this for 2 reasons – a) I did not want to desolder the assembled “U” girder upright, and b) 144 degrree solder can flow with my small 25 watt iron on the large heatsink of brass that is the Whitton truss bridge side
|One span, with two "U" beams fitted, and braced, and after removal of the temporary brace|
The result was very strong, and I felt confident to remove the temporary brace, designed to stop the 2 bridge sides from collapsing inwards with handling.
I made a minor change to the assembly order of the subsequent “U” girders. Basically, the 2 uprights were installed, soldered, and braced, before the overhead beam installed. This was a lot simpler than my earlier method.
|Detail soldering of one of the venter uprights|
Angle braces were fabricated, and soldered to all 4 “U” beam assemblies. These are purely cosmetic on my model.
I have been using fluxes to aid the soldering, and these need to be removed. I have scrubbed the girder with kitchen cream cleanser, and washed the lot in water. Further treatment will be needed prior to painting, but at least the model is no longer a clothing stain hazard.
As you can see, I still have to fit "U" girder supports to the second span. Followed by painting, and then the sleepers and track can be added.
This process is very time consuming. I have not added up the hours I have spent – but my last “U” beam assembly took just over 5 hours to fabricate, and add. I am sure that talented modellers might have used 3D printing to make the “U” beams - I am not in that category
Happy to report that after 3 weeks, the shingles pain has much reduced. Whoever said Model Railways is therapeutic must have had me in mind. I will continue with fitting the “U” beams, and with luck, will have painted the bridge for my next bridge blog post.