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THE NMRA HO STANDARD

There are several tools that ANY model railroader should never be without.  One of them is a gauge.  Now, if you are modeling in "fine" or "prototype" scale then this is all the more reason to have a gauge.  The fine scales are even "pickier" about perfection than the NMRA standard shown here

There are four parts of this gauge that I use religiously.

1. Flange to Flange.  Sadly, many of our kits and even ready-to-run engine wheel sets are out of gauge from the factory.  This is not the case with purchased wheel sets but I have seen my share of these that don't meet spec.  Most of the derailments I see are caused by flange to flange problems.  This is the first thing I check for when a car derails.  Cars and locos with proper flange to flange distance will tolerate a lot of track misalignments and "issues".  If they are not gauged properly then they can derail even on smooth, even track.

2. Track width.  Track that is "out of gauge" is the second leading problem of derailments.  If one car leaves the track in a particular place or places on the track consistently (more than twice) then besides the car wheels being out of gauge, the track is probably to blame also. 

3. Clearance.  Maybe you are still not having fun.  Your engines and cars are all in gauge and the track is in gauge but it still jumps the track.  Try the clearance gauge.  Now, side scrapes are obvious and usually make a noise but how about the ones that are close to the track and just big enough to cause a GP40 to derail at the turnout every time.  Try your clearance at rail height.  An Atlas "Snap Switch" with the older "track side mounted " solenoid had a tight fit with the inside screw and the cow catcher or steps on most GP's.  The fix is easy but boy did it take me a long time to find that one!  The gauge is made to check this too.

4. Flatness.  The gauge was not designed to check for flatness but I use it all the time over joints to insure that there is level track.  Many a derailment has been caused by "bumps" in the rail.

5. Flange depth and tire width.  Older or cheaper "toy" cars and locos can have a tire whose flange depth can be a problem, usually at turnouts or crossings.  Tire width is not a problem with finer scales but if they are too skinny then they will drop in the clearances of most NMRA made turnouts.  Flange depth problems with the track is hard to find and replacing the wheels is the only way to fix this problem unless you want to change out everything and hand make some turnouts.

More at: http://www.nmra.org/standards/gauge.html

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This page was last updated: 2009-11-30