Flanges and flangeways at NMRA standards (July 2009) S-3.2 and S-4.2

I don't know if the following is a "good reason", it's just my reactions to the numbers.

The Target flangeway depth is 0.048". The tolerances are asymmetrical, ie, the minimum flangeway depth is further from the target than the maximum. In practice, manufacturers will set up jigs and molds for symmetrical tolerances, so their minimum flangeway will be considerably more than 0.025".

The minimum flangeway does matter to people who build turnouts, however, as they typically fill the frog with solder, then cut flangeways (that's what I do.) There's no point cutting flangeways deeper than necessary, so 0.025 is OK as a minimum - it provides for zero interference between an RP-25 wheel and the flangeway filler.

Does that answer your question?

wolf k.

Hi Wolf,

I quess you are mixing flageway depth (H) and flangeway width (F) on Standard S-3.2.

The flangeway depth (H) is only described as single limit, the minimum depth. The minimum flangeway depth is smaller than the maximum wheel flange depth (D in S-4.2).

The flangeway depth is smaller than max. flange depth in almost all smaller scales in NMRA standards S-3.2 / S-4.2 of July 2009.

There must be a reason, but I still do not understand it.

pekka

Yes, you're right. Shoulda double checked.

Now that I double check the numbers, I'm as puzzled as you are.

H'm.

wolf k.

About as expected. The track gauge for HO nas never been in line with what the other scales are for a relationship between the wheel gauge and the track gauge. They really don't care as what they have is "good enough".

-- Bob May

rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net

In message , Bob May writes

Got this from an NMRA British Region member. Hope it helps.

Mike,   It is interesting that this apparent discrepency is true for all scales except O Scale.  In O Scale there seems to be at least 9 thou clearance in the worst case.   I have found a prototype for this - see attached photo.  As can be seen from the markings, the flangeway depth is less than the flange depth giving relatively smooth transit over the crossing.  I found this one in Rome but I also found an example on a mainline/tram flat crossing in Caulfield, Melbourne.  It is only suitable for slow speed.

This is the way trams/streetcars usually work: the wheel tyre is narrower than the rail head so that when -- in time -- the rail sinks into street pavement the wheel sides will not get in touch with paving stones. As the width of wheel tyre is narrow the wheel width is not sufficient to carry the wheel on wing rail over the flangeway just ahead of the crossing nose.

This is the way hi-rail model trains manufacturers in Europe are working: the oversized flanges of most european rolling stock forces the flangeways to be wide. To avoid having enormously wide wheels to match, they too have selected to run on flange at the crossing.

Due to constant strive for closer to prototype looks, model railroaders aim at more and more prototypical flange deepness and overall wheel dimensions. Forcing the wheel to run on the edge of the flange prevents the possibility to reduce the flange depth further, and causes bad pickup and possibly derailments. Why?

If the plan is to run on the flange edge, the flange and flangeway depth must always match. Otherwise the wheel will rise or drop at crossing. As rigd wheelbase is supported by three wheels (forming a plane) the fourth wheel will no longer carry any load or be in contact with the rail head causing possible derailments and bad pickup.

If the NMRA plan was to allow running on flange edge, then there should have been both limits of depth (max and min) for flangeway and flange depth and a demand for all metal crossing or at least conductive flangeway base, as it may well be that the flange running along the bottom of crossing is one of the three wheels carrying the load and carrying the pickup -- as no three-point suspension or springing is demanded either. Pinpoint bearings do their best to provide some flexibility to rigd wheelbase, but is this good enough in practise? There is no help for steam locos with solid inside bearings.

So -- if the plan is to allow running on the flange edge then the standard seems to lack one or two dimensions or footnotes (there is a full list of footnotes in european counterpart standard, NEM-310 by MOROP).

pekka

In message , Pekka Siiskonen writes

Thanks for your comments. I've passed it back. I'll let you know what they say (it may take a bit of time and as I have the memory of a goldfish feel free to remind me in around 10 days or so if I haven't posted anything)

Mike Hughes wrote: [...]I have the memory of a

Hey, _actual_ testing pf goldfish showed they can remember what they've leraned two to three weeks. Better than some of Senior Humans. ;-)

There are mistakes in the NMRA standards and this may well be one of them! I'm not aware of any mistakes in the standards that I have utilized that cause any disasters. 0.003" of clash is a very small "bump" for a flange to ride over :-)

For my own use, I combined the NEM and NMRA standards (because I have a mix of wheels) and use the result for my own layout and rolling stock. This results in some tight tolerances in both track and wheels, but I consider them to be workable.

Regards, Greg.P. NZ