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Minimum tunnel height

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Posted by ATLANTIC CENTRAL on Thursday, June 1, 2017 8:12 PM

    

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Posted by RR_Mel on Thursday, June 1, 2017 8:25 PM

gmpullman

 

 

I believe there are three NMRA gauges in HO. Old Time, Classic and Modern.

http://www.nmra.org/sites/default/files/standards/sandrp/pdf/s-7_2012.02.pdf

There have been several revisions over the years. Mark II, III, IV and now IV-b.

Regards, Ed

 

The gauge I have must be a Classic NMRA HO for standards Gauge, H measures 3.031”/76.97mm.  It is labeled Mark IV, I also have a older HO gauge that doesn’t have a label and it is the same size as the Mark IV.  I can’t find anything but the HO Mark IV online.  Can someone clue me in to the difference size Standards Gauges.
 
 
 
 
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Posted by DSchmitt on Friday, June 2, 2017 2:31 AM

I don't think, there are three different different NMRA gauges, but the modrler can make their own from the information on Atlantic Central's link. 

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Posted by rogerhensley on Friday, June 2, 2017 5:28 AM

Perhaps this will help explain how railroads set tunnel clearances. http://madisonrails.railfan.net/eci/gauge.html

 

Roger Hensley
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Posted by RR_Mel on Friday, June 2, 2017 8:25 AM

DSchmitt

I don't think, there are three different different NMRA gauges, but the modrler can make their own from the information on Atlantic Central's link. 

 

That’s good info.  Thanks for unscrewing my head.  Sometimes new stuff really does a number on my 80 year old brain.  On my tunnel portals I added a ¼” clearance to the HO Mark IV NMRA “Classic” Standards Gauge.   As stated earlier better safe than sorry.
 
Good topic!  Great responses!
 
 
 
 
 
Mel
 
Modeling the early to mid 1950s SP in HO scale since 1951
 
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Posted by railandsail on Saturday, January 26, 2019 1:06 PM

Tunnel Clearances

Is the true tunnel clearance measured from the railhead, or from the roadbed base line?

In our modeling we need to allow for the depth of the rail and the ties to get our existing trains thru,...and future purchases.

What brought this subject up in my mind was my checking, and rechecking that I could get some overlaping tracks (verticial ones) to fit in my helix-to-shed bridging. I was working with roadbed to roadbed dimensions, but a few circumstances had me looking at railhead to underside of overhead roadbed material. (did that make sense? Confused)

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Posted by mbinsewi on Saturday, January 26, 2019 1:10 PM

railandsail
, but a few circumstances had me looking at railhead to underside of overhead roadbed material.

I never built a helix, but if I were, that measurement makes more sense to me, as that is the actual area you need for your highest rail cars, and some space in case you have to get your fingers in there.

Mike.

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Posted by dehusman on Saturday, January 26, 2019 2:26 PM

railandsail
Is the true tunnel clearance measured from the railhead, or from the roadbed base line?

Railhead, i.e. top of the rail.

The clearance is determined by AAR "plates" which give the clearance diagrams.  They have evolved over the years.

Here are diagrams of the plates:

http://www.icrr.net/plates.htm

They apply to any structure (bridge, tunnel, building, etc).

Earlier railroads had tighter clearances, but they were widened as the railroads bought bigger equipment.

Dave H. Painted side goes up. My website : wnbranch.com

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Posted by NHTX on Saturday, January 26, 2019 8:27 PM

     Fittng newer equipment through older tunnels results in some interesting solutions to the problem out there in 12"=1' land.  A lot of tunnels had their floors lowered to accomodate the taller cars.  This caused track to ramp down into and up, out of the tunnels.  Other railroads  cut triangular notches high and wide enough to permit the passage of Plate F equipment through old, arch roofed tunnels.  In some cases it looks like it was done by ramming  instead of cutting away the excess material.  The latter fix would be interesting on a model railroad.

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Posted by ATLANTIC CENTRAL on Saturday, January 26, 2019 8:56 PM

railandsail

Tunnel Clearances

Is the true tunnel clearance measured from the railhead, or from the roadbed base line?

In our modeling we need to allow for the depth of the rail and the ties to get our existing trains thru,...and future purchases.

What brought this subject up in my mind was my checking, and rechecking that I could get some overlaping tracks (verticial ones) to fit in my helix-to-shed bridging. I was working with roadbed to roadbed dimensions, but a few circumstances had me looking at railhead to underside of overhead roadbed material. (did that make sense? Confused)

 

The NMRA has revised their standards and recommended practices, but for the most part, the clearance has not really changed - 3-1/32" above the rail head for all post 1900 modeling except for the most modern equipment.

Why is this even a question at this point in this hobby?

Here is the link again:

https://www.nmra.org/sites/default/files/standards/sandrp/pdf/rp-7.1_tangent_track_centers_and_clearance_diagrams_july_2017.pdf

So obviously one needs to know what construction method they are using and add that total, subroadbed, roadbed and track, to the 3-1/32" for a rail head to rail head number for calculating grades - I use 4"...........

Sheldon 

    

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Posted by selector on Sunday, January 27, 2019 3:01 PM

railandsail

... but a few circumstances had me looking at railhead to underside of overhead roadbed material. (did that make sense? Confused)

 

It's the only way to think of it if you want to keep it simple and to avoid costly errors.

Doing a thought experiment, you imagine the highest rolling stock you have, or are thinking about purchasing, say double stacks or the stack on a steam wrecker crane, or maybe the boom's cable guide gantry.  Better yet, why not extract that item from its box and place it on rails.  Measure its lower comfortable limit for overhead clearance, and then use that to add to any roadbed and sub-roadbed thicknesses you intend to place where tracks cross over each other at disparate grades.

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Posted by SeeYou190 on Sunday, January 27, 2019 5:02 PM

RR_Mel
I used the HO NMRA gauge plus a ¼” for my tunnels and they look pretty good.

.

I don't use a gauge. I couple a TOFC flat and a Rivarossi observation to my 2-8-8-4 EM-1 and run it through the tunnel. If that train can make it, all my equipment will be OK.

.

-Kevin

.

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Posted by BMMECNYC on Friday, February 8, 2019 3:27 PM

For a helix, I would think that you would want to add at least a finger width, maybe a bit more so you can safely extract equipment of median height in the event of a mishap.  Tunnel, maybe a bit less.

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