Risers required for a tunnel

[mijj]

I think I am about to start on the model railway again. Knowing zilch about it and needing a tunnel, what risers will I need - bare minimum would be a starting point.
Jim.

[Bandit Mick]

Sorry, I don't understand. Why do you need risers for the tunnel? I made then placed my tunnel on my layout then built the banks around it.

[Tricky Dicky]

Not sure what you mean by risers Jim. If the intention is to have another track go over the tunnel and you wish to raise the crossing track then probably the best move is to look at what you will use for a tunnel portal and the absolute minimum would be to clear the tunnel opening.

Making tunnel entrances look right is quite an art since very few just simply disappear into a vertical cliff. Most tunnels start off as a gradually deepening cutting till eventually it is deep enough to continue as a tunnel.

Richard

[Walkingthedog]

Do you mean how much clearance under the tunnel?

[mijj]

I thought I understood what I meant. Now I'm not so sure .

I will need to have the min. height that WTD says. I won't need any riser height until that is in place as they (Woodland Scenics) provide risers in inches etc. They also say 4% slope so I hope that is ok.

I did save an image that someone here gave that showed the minimum heights for tunnels and things but it's Australian, well it can't be found as it's gone walk-about.
Jim.

[Walkingthedog]

So you want to have a track passing over another track. The minimum for a gradient is 1 in 30, that is 30 inches/cm to rise 1 inch/cm.

[Brian]

To add, in OO you need a minimum of 60mm from lower level rail top to the underside of anything passing over.
Note measurements are taken from lower level rail top not baseboard level.
A OO structure gauge is shown on my web site here https://www.brian-lambert.co.uk/Hints_& ... Bookmark16 and below that is a link to a multi gauge/scale structure gauge.

[Bandit Mick]

If you want to look at my tunnel (it’s by no means perfect) go to members layouts and look at the layout called Ty Mawr. It might give you some ideas. Again, I’m no expert I just try things out until I’m happy with them.

[teedoubleudee]

Jim, if it helps I am currently building my new layout to include a track crossing over another track at one end with them at same level at the other. First time I've ever built a layout that wasnt completly flat! After a lot of studying the basics and some testing using books etc for the inclines, I have gone with the "halve it" method (my words but not my idea) where you achieve the clearance height required by inclining downwards the lower track to half required height and incline upwards the upper track by the same amount(if that makes sense!).

So in my case, I have a total base board length of 3300mm. Starting at baseboard level zero at one end I raised a single track by just over 30mm in approx. length of 2000mm (1 in 66). The over track which I have yet to start building will rise from this end (base board level plus 30mm) by a similar incline so it will pass over the lower track with a height difference of 60mm at the other end. 60mm is really an absolute minimum but testing shows that my diesel railcar clears it no problem and can zip up the incline with no problem at all. I could have made it a few mm steeper as 1 in 66 is fairly generous but I am really happy with progress and my results so far. Hope that helps.
Terry

[mijj]

Thanks all for the visuals and measurements. I like the idea of splitting the up by going down half-way Terry but the way I'm doing this I'll have needed to plan that in. I have approximately similar length/span of 3m as yourself. But I failed to plan - that means I've planned to fail!
Ah well, have another cuppa and think about it.

I'll go to the garage tomorrow and remind myself of the measurements. I've done virtually nothing since last summer, what with one thing and another.
Jim.