Sunday 12 February 2023

Thomson River - 13

 I expressed surprise that it was the end of 2022 and how quick the year had gone on my last blog, and here it is nearly half way through February 2023. I swear that time is speeding up (anyone in the older boat will vouch for that).

This is the first post for 2023 and I will finally announce that I consider my build of the Thomson River bridge done!

Early planning 2016

 When the layout was initially planned, I wanted to put in a few signature structures, what could be more impressive than a few bridges. The one that most people would be familiar with is the curved timber trestle over the Monbulk Creek and just outside of Belgrave on Puffing Billy. So that was the first one that was tackled. It wasn't all that complicated to build and it's construction was probably covered in some of my earlier blog entries if you are interested.

The second structure I chose to model was going to be the Thomson River bridge located on the Moe to Walhalla line and thankfully still in service on the Walhalla Goldfields Railway. Both of these iconic bridges are luckily still accessible  for viewing. The original baseboard constructed in the photo above was mainly guesswork on how long and deep to model would take up. This section was always going to be 'a coming back to finish' baseboard, so a temporary track was located towards the back to enable initial construction to commence (one day)

Parts of the bridge are laid out in their approx. position

 Luckily a set of unreadable plans of the bridge were available and they were a great help in the bridges construction. During the early days I was lucky to get help from two friends, Roger Johnson who 3D printed the piers and Nathan Wakim who laser cut the lattice and side girders. Without the help of these two gentlemen the bridge would not have turned out as well as it could.

The lattice girders slowly take shape

 It was a slow build as there were many unknowns to overcome along the way. The centre lattice girders were probably the most complex to construct. They required the drilling of many holes to insert a styrene rod that separated the two sides, then X shaped spacers were made and inserted with the tweezers. Luckily I only put the rivet decals on the visible side. It was success when the outside girder was made, then the realisation the second one had to be done as well. What is even sadder is that when the bridge is in place most of the wall side girder is not visible.

Centre lattice takes shape.

I won't go fully into the individual sections of the bridge and how they were constructed but give a general idea on how all the bits came together. Thankfully over it's build I took a few hundred photos for the record. All together I reckon that the build has taken around three plus years to complete and I admit there were also other sections of the layout that were worked on when I needed a break from bridge building.

Core strength of the bridge
The photo above shows what the bridge was constructed around. This piece of U shaped aluminium was cut to the bridge length - around 1.9 metres long and was eventually sandwiched with all the pieces of timber and styrene required. In fact it was that solid, it could be suspended from both ends and have no significant sagging. The above photo outlines maybe why it build took so long. The short pieces of timber had to be cut to around 5mm long and then glued right across both sides of the near two metres of bridge, there are probably a few hundred in position.

Underneath the centre span
There are some saving graces when structures are constructed. One is the fact that will all surfaces be visible when it is finished? The first time saver in my bridge was the fact that I didn't need to replicate all the rivets on the wall side. These decals were a pain in the butt to get into the right place. I had close up photos I had taken and tried to duplicate the positioning of the decals to match the real rivets. Time consuming but satisfying in the end.

I decided right from the start that I would model the underneath of the bridge even though most will never be seen. So even if I got it wrong in the build most will never know. It is mainly in the section across the river that upshots can be taken. So when the underside was finished I decided to give it a rusted effect, this I was particularly happy with, alas never to be seen.

An ant's view of the bridge all weathered
With the completion of the underneath of the bridge and the top, it was time to start developing the scenery on both sides of the bridge down to the river. Some of this work was covered in the previous blogs.

Landform down towards the river

 Also mentioned earlier was the piers produced by Roger were forwarded to the maestro painter Ian Fainges for him to paint up and weather. He did a fantastic job as can be seen in the photos. As another distraction I made up the five timber trestles that hold up the outer edges of the bridge, no two were the same. These were based on the original plan drawings and not what are currently there.

So all these elements eventually came together, the two river sides were sceniced, the river was poured and all that remained was to place the piers and trestles into position and place the bridge on top. Most of the scenic work and river pour took place when the bridge was not in position, which made it a lot easier to work on.

Bridge section aligned with existing baseboard

As the above photo shows both sides were secured to the existing baseboard, with some shimming required to get the level perfect. Also can be seen the temporary track that was in position for a while during construction. One by one each pier was shimmed up to allow the base rest up against the base of the bridge. A small spot of glue was put towards the back to hold in position and also the base was glued. The bases were to be surrounded by scenery so any evident glue would be hidden. Then it was just a matter of securing the timber trestles into position. Just to complicate the build, the piers and trestles were at an angle and not perpendicular to the bridge structure. I had made an angle template at an early stage that came in handy towards the end.

Overall picture of bridge
The photo above shows the bridge in position and also the offcut piece of aluminium that was screwed upside down over the centre section for support. It was necessary to reduce the supporting web of aluminium to accomodate the higher lattice section. There was only a thin section left and that eventually had the supporting timbers glued to it. This work of milling out the centre section was performed by Russel Freeman on his milling machine, a task that I could never have completed. It was only when the whole bridge was resting on the piers that this section of aluminium was removed, otherwise it would have buckled.

The supporting aluminium ready for removal

 With all piers in position it was then time to remove the supporting aluminium and think about the track laying. I thought back about all the work I had done on the bridge and wondered if some hand laid track would look okay. I didn't think for too long and went back to the standard Peco narrow gauge track I had been using. I had used it on the Monbulk bridge and when ballasted it came up looking alright. There are two things I don't really like about the Peco track, one is the ends are modelled too decrepit for my liking and also what the heck are those rail fastenings modelled on? They must be big spikes. So what I did was to cut off some of the decayed ends of the sleepers with a blade and then reducing the size of the rail fasteners which was also a pain job to do. It basically required going across the two metres of bridge four times to reduce the size of the rail fasteners. See the photo for what I mean.

Reduced size rail fasteners on left hand side, original on right

 The sleepers if matched up against the real Puffing Billy ones are too short but other than hand laying we are stuck with this track. Another thing I did was to cut the rail at 25 foot intervals and insert fishplates around the cut. Probably something that won't be noticed with visitors, but I know they are there. The track and rail sides were also painted.

Fish plates and painted track


Ballast slowly creeps outwards

Basically the last job to be done was to lay the ballast across the bridge. I laid some out from the baseboard edge to see how it would go rather than do the lot and find  something wrong. It was just one of those jobs where you do it bit by bit and finish off.

Ballast is all in place
It was just after I had all the ballast in position and I thought 'that's it, I'm done' but looking at the actual bridge there were two safety refuges hanging off each side of the bridge I forgot to install. I had actually made both timber bases some time ago, but needed to make the steel railing around the edges. The current one has an intermediate railing but the plan shows the original with just the top rail support. I used that plan as my justification to copy that model. The model had their railings installed and suitably rusted up and then glued to the sides of the bridge. A supporting steel pipe held it in position.

Safety refuge

So after the safety refuges were in position I declared the bridge finished. It was one of those projects that seemed to go on for ever but it was something to enjoy at the end of the build, now I can annoy people with countless photos of trains on the bridge!.

Drone shot
The bridge being put to the weight test

As with most new sections of track in the real world, freight trains are often used to settle the track down before passenger trains are operated over the same track, so although you can see that freight is now using the bridge, the official opening is still due to happen, I hope this will happen soon.