Acceptable track width

[rperego]

I posted a problem earlier concerning drag on a curve.  After checking my track width in various places I'm wondering if this isn't the problem. 

On straight sections I'm averaging about 1.787.  However, on the curve I'm having the problem on I only measure 1.740.  Most of my curves are measuring less than the straight sections.   The cars that are dragging have plenty of slop sideways but I noticed when I positioned a Shay on the curve in question I can't move the trucks sideways hardly at all.

My track is all USA.  I was pretty careful when laying it out not to torque the curves - in fact I laid out complete circles first and made sure the diameter was the same at various points before establishing various portions of circles.

Is 1.740 unacceptable?

Thanks, Bob

[r.cprmier]

You are talking about .047 difference.  measure the width between the FILLETS and ROUNDS, as this will be the area that mostly is intimate.

If you have no reasonable slop between on curves, you are inviting a number of problems, derailments for certain.  Double check your curved always.
Incidentally, fillets and rounds would be the inside-to-inside of the wheel, where the flange starts, and the rounded inside to inside portion of the railhead.  There is no real dyed in the wool dimension, but there are acceptable tolerances.  Check the NMRA specs.

RIch

[Barry BBT]

Just a note,  NMRA do not have specs to which any track or train have been built.

The track is gauged at 45mm or 1.771".

The wheelset Back-to-Back is 1.575"  or 40.04mm.

The first issue of NMRA specs indicated the back to back in one scenario as being wider than the outside of the rails, since corrected.  NMRA is in a catch up mode, deving specs faster than they can be applied. 

G1MRA has the standards used in large scale since the beginning of the current rage.  The standards have been in existance for over sixty years.
Check:     http://www.nmia.com/~vrbass/steam/g1mraform.htm

Barry - BBT

Check:     

[r.cprmier]

Barry;
I could be wrong, but it was my understanding the the NMRA did in fact, have spec standards.  Model Railroader in the late 60s, early 70s did publish specks for RP-25-which I believe is an NMRA standard.

RIch

[hobo]

The short answer is no 1.740" (44.196mm) is not acceptable.

All G/large scale track is based on #1 gauge standard of 45mm inside rail width.  This standard originates in Europe and has not changed or will not be changed by the NMRA.

However, the NMRA is attempting to incorporate this standard into its Standard Pratices and Recommended Procedures for our (modelers) benefit. So using their chart in Standards 3.2 the minimum width between the rails is 1.766" (44.85mm). The maximum width is 1.793" (45.5mm).

So now you need to determine why your track is not within the standards.  You will need to make a compas to check the curve/radius of the individual rails of your track to determine which rail(s) are bent incorrectly.  Once your know which rail is causing problems you will need to correct the radius.

You may want to check to make sure the rails are not twisted or leaning.  The rails may have to correct radius at the bottom but the rail head may be leaning in towards the opposite rail causing your space between the rails to be reduced.

[rperego]

I'm not sure what the name is of the points where I measured some wheels, but from where the angle begins on the flange I measured between 1.755 and 1.765 on a number of Bachmann car trucks and wheels of locos.  This explains my problem on the curves - the wheels are riding up where I have less than around 1.765.  I watched closely and sure enough, this is what is happening.

Next question is, how do I fix this or did I maybe just get defective track?  The track doesn't move within the plastic keepers so I'm not sure how I can increase the width.  Any thoughts?  I will check that the rails aren't leaning in.  I thought about this when screwing them down, especially because for a holiday layout I first covered the board with a white felt type material - it could be the ties where the screws are have depressed in the middle causing the rails to angle in - although one would think I'd have the same problem on the straight sections.


Thanks, Bob

[Kevin Strong]

I could be wrong, but it was my understanding the the NMRA did in fact, have spec standards.  Model Railroader in the late 60s, early 70s did publish specks for RP-25-which I believe is an NMRA standard.

In the context of large scale, they do not. They published large scale standards in 2004, but they've gone virtually unnoticed and largely ignored by the large scale manufacturers. The NMRA set forth to revise those (and all scales') standards in July of this year. The proposed large scale standards have been tabled pending a thorough review and revision into something that actually (a) makes sense, and (b) has more than a snowman's chance in Phoenix of being accepted by the manufacturers. The folks working on this review are long-time large scalers (not necessarily NMRA members) who understand the history of the hobby and the "large scale" way of doing things. It will still be up to the manufacturers to adopt these standards, and maintain enough internal QC to keep in step.

Later,

K

[rperego]

I fixed the problem areas by loosening the outer rail connectors so they could separate if desired, and forced the rails wider by using toothpick ends as wedges.

I measured some never installed curved track and found that in nearly all places the ID is less than straight track sections.  Also, as I experienced with track I installed, in some places the ID is unacceptable.  I now know when installing to check the width everywhere.

Thanks for the advice on the min and max standards.  The 1.766 min. sounds reasonable given the most I measured on various wheels I checked was 1.760.