Prototype vs model clearances

[Redvan]

I'm curious as to what a good clearance height wouild be when having one track cross another....1.5", 2" or more?

I'm using N gauge in a tight area that will have a few helixes and I have created them with a grade of 2.3-3.0% which affords a clearance of about 1.5". Taking into account whatever substrate I decide to use under the track plus the height of the track itself, this clearance comes down a bit. Luckily I'm just in the planning stages using AnyRail.

Any suggestions?

Mike.

[selector]

This is not an easy or straightforward question to answer.  For a simple overhead, say a girder bridge supporting ties and rails, you'd want little more than 2.75" (HO) from the bearing surface of the rails being passed over...the bottom tracks.

A helix is another beast.  For one thing, you have to leave room to get at least finger tips under the overhead structure to retrieve or to nudge or recouple items of rolling stock that derail or decouple or stall...whatever.  Your fingers don't change scale much from HO to N. 

Whatever the conversion ought to be, say a simple 50% from HO to N, then you should be safe with a simple overpass of about 1.4" of clearance between the nether rails and the bottom edges of the top structure.  If you have a pantograph, add another 3/4" in N scale..?  If you want to reach into a helix, maybe that 3/4" is light for your fat fingers.

[gregc]

an NMRA gauge provides that info and more

 

[cuyama]

Welcome to the forum. NMRA S-7 is a great place to start -- the "H" dimension is vertical clearance -- it varies by era of equipment.

For a helix, be sure to allow for subroadbed, roadbed (if any) and track height when figuring the remaining clearance. And you may need to get fingers in there as well. Some methods of supporting the subroadbed (like a bar beneath) may also reduce the clearance.

Note also that the tight curves add to the effective grade of the helix itself and very tight curves may be prone to stringlining (derailing across the center of the helix).

Good luck with your layout.

Byron

 

[carl425]

Redvan

I have created them with a grade of 2.3-3.0% which affords a clearance of about 1.5".

If my math is right, you're asking for trouble.  1.5" / .03 = 50" circumference.  50" / 3.14 = 15.9" diameter or 7.95" radius.  I've been told the 16.5" radius helix I'm planning to build is pushing the envelope.

[cuyama]

Good point, Carl, I only looked at the clearance question and didn't consider the (apparently) unworkably tight radius.