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One of the things I will have to do is cross a path that is one paving slab wide at an angle of 45 degrees (ish). I think it will work out as just over a metre (3ft). The other thing is that I want this section to be easily removable.

Construction wise, I've seen mild steel being used for some gaps. I've bridged a smaller gap between my Dad's indoor baseboards using ply glued between aluminium angle sections (15x15x2mm) and that has been plenty strong enough for the gap (60cm) whilst being light, removable and not having a great depth.

For outside I was wondering whether a similar construction but using mild steel angle section of say 20x20x3mm with 18mm ply for the track base would work. Keeping the depth of the bridge deck down would allow for a more realistic bridge to be built up. Thinking something like the Tomatin viaduct or the Loch Awe viaduct.

One of the things I've been meaning to learn for years is to weld (I have a 31 year old Rover in the garage waiting on that too) and this is the kind of project that would be easy to learn with.

Has this been tried before or am I looking at a non-starter?
 

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The main span on my Northern Viaduct is a piece of repurposed timber 5 feet long and 20mm thick.  It's now been there for nearly 8 years without any significant sagging.  As you seem to be proposing a shorter, removable span, it will be much easier just to go for timber and see what happens.

 

20200509_181540.thumb.jpg.2f930c87a6b7872ffc8c9b8544959068.jpg

 

 

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10 hours ago, Clay Mills Junction said:

....Thinking something like the Tomatin viaduct or the Loch Awe viaduct....

Did someone mention viaducts? 😃 Now we're talkin!

For a removable span of around a metre I wouldn't think you'd need anything too substantial. It should be relatively easy to provide sufficient support for a short length of baseboard to prevent any sagging. Looking at photos of the two viaducts you mention it might even be possible to obtain metal section that looks similar to those girder sides so that it could form part of the design rather than being just there as a support for the track base. 

I had a slight bow in the track base that spans across from my large viaduct onto the elevated boards that run along the bottom of my garden and I actually used the 'U' section uprights for adjustable shelving as I had some spare from when I fitted out the shed. I'm not saying that's something you could consider but just showing that almost anything similar could be used. Lengths of square steel rod embedded in the aerated blocks support the two girder bridges on my large viaduct.

I'm not very technically minded but I'd be looking at finding something that resembles those girder sides and if you fancy some welding maybe you could use metal for the track bed too and do away with the plywood. It should still be relatively easy to handle, it wouldn't matter if it got caught out in the rain and it would give you the depth you need. Yes, that's it...go for the full metal build - I'd love to see that.

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51 minutes ago, mick said:

Did someone mention viaducts? 😃 Now we're talkin!

For a removable span of around a metre I wouldn't think you'd need anything too substantial. It should be relatively easy to provide sufficient support for a short length of baseboard to prevent any sagging. Looking at photos of the two viaducts you mention it might even be possible to obtain metal section that looks similar to those girder sides so that it could form part of the design rather than being just there as a support for the track base. 

I had a slight bow in the track base that spans across from my large viaduct onto the elevated boards that run along the bottom of my garden and I actually used the 'U' section uprights for adjustable shelving as I had some spare from when I fitted out the shed. I'm not saying that's something you could consider but just showing that almost anything similar could be used. Lengths of square steel rod embedded in the aerated blocks support the two girder bridges on my large viaduct.

I'm not very technically minded but I'd be looking at finding something that resembles those girder sides and if you fancy some welding maybe you could use metal for the track bed too and do away with the plywood. It should still be relatively easy to handle, it wouldn't matter if it got caught out in the rain and it would give you the depth you need. Yes, that's it...go for the full metal build - I'd love to see that.

It looks like there might be some square perforated sheet or steel mesh that could be cut up for decorative parts but whether it would suffice for the strength I wouldn't know until I had it.
I'd considered a purely metal structure but was concerned that nothing between metal and track would create a danger of shorting. Even if what is under the track is just a thin layer of plastic. I suppose a perforated sheet under the track painted in plasti-dip would insulate enough, allow water to drain straight through, insulate it from heat and support the track. That actually sounds like it would work. Even plaster edging strip with some edging might look OK painted up from a distance.

I do prefer having some vertical edging to the bridge to prevent expensive models taking a dive onto concrete slab.

Some research into what materials are available is my next step I suppose.

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I don't think there'd be any problems with 'shorts' between the track and a metal bridge as the plastic sleepers would be sufficient insulation between the two. We use plastic rail joiners to insulate adjacent track sections, such as with live frog points, and the little pip that separates the two is only a few millimetres wide and it works well enough.

I think it would be worth looking to see what's available to form the vertical sides and offer you the safeguard of nothing coming over the top. Could be a nice little project.

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Looking at one or two other WHL bridges, I can see one where the lower section uses steel panels rather than lattice, so for that I could do by turning the L around and dropping the track bed a few mm. There is the option of painting the angle section black to hide it then tacking on latticework in-front of it in light-blue or red oxide colour.

Also, the Loch Awe viaduct has quite wide walkways either side with wooden planking so the flat area either side isn't unrealistic. A finer mesh could be tacked on vertically to make the sides.

The only thing I wouldn't be able to do is replicate the thousands of rivets that these bridges were built with.

bridge X section.jpg

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