Tunnel portal clearances?

[Ray Dunakin]

On a typical 1:20 scale narrow gauge railroad, how much clearance (top and sides) should there be on tunnel portals?

[Ray Dunakin]

Wow, I thought someone would have replied by now.

I have blueprints for tunnel clearances on a prototype railroad, but it's standard gauge so I'm not sure if it would be correct for a narrow gauge line. On the other hand, perhaps a 1:20 model (with much sharper curves than a real railroad) might need extra clearance.

[ttrigg]

Ray:

For my tunnel clearances, I did a trial and err method. Long before putting the track and tunnel "in the dirt", I built my "prototype" on the patio. I then moved things around until I could get the longest cars through the tightest curves in the smallest tunnels. Took the clearances needed for a 4 ft dia, and applied to ft dia curves and to straightaways too.

[Neiler]

I rarely reply but you've struck a nerve. I've been translating track spacing from other scale tables and the same could be applied to height clearances. Using On3 as 4.25" high x 48 (feet) and divide by 20.3 (I assume that is the largest scale model you'd run - 7/8" is another story) and you get about 10" clearance. Jack Verduchi (sp) uses a 12" dia flex drain pipe to set the track in for tunnels. My thought is that might be a little tight for some models - not in width but max height. I'd be curious to know what you decided on.