Free-mo Curves

Gary Green

February, 2018


At a recent Free-mo event, a new module anticipated using 30” radius curves that would be used by “mainline” or “through traffic” trains. This led me to look back at the Free-mo standard regarding curves.


From the “Official Free-mo Standard:”


S3.12 The minimum permitted curve radius on a through route of a Mainline Module is 42 inches. This includes through track sidings and other tracks where through traffic will run.


What’s important here is that the 42” minimum applies to all track types through which “through traffic” or “mainline” trains will run. Given that mainline trains are anticipated, a radius of less than 42” on the module described above would violate the standard, even if some or most mainline trains could run through the sharper curves successfully.


Note: Some years ago, we found that not carefully following the minimum curve standard on the curve leading into and out of a siding caused problems. Even those very short curves need to conform to the standard. Curve templates can be particularly helpful in cases like this.


From “Free-mo Standards for Branchline Modules:”


BL-S3.12 The minimum permitted radius on the through route of a Branchline Module may be less than 42 inches but shall be no less than 36 inches. This includes through track sidings and other tracks where through traffic will run.


The branchline standard includes this warning: “If you build to the branchline standards, your setup opportunities might be limited. Branchline modules are not always accepted in a Free-mo setup.”  As an example, a module with a 36” radius curve was excluded from the mainline of the Free-mo layout at the 2011 NTS layout in Sacramento. We placed it at the far end of the yard and engine terminal area where no mainline trains would run because we didn’t want to risk problems or derailments. We always asked for curve radius information when accepting modules for the layout. Were we typical in this regard? I have no idea, but we knew that curves of less than 42” radius have the potential to cause problems with some of the equipment typically run on Free-mo layouts.


A further comment:


It isn’t uncommon for someone to say “my boxcar runs through the track just fine” as a test of trackwork, never checking the trackwork with a Mark IV NMRA gauge. That’s backwards since the NMRA gauge, not the boxcar, is the “gold test” of certain aspects of trackwork like track gauge, flangeways, and flange clearances. Likewise, if I build a curve on my module that is sharper than the standard and say that it’s OK because my test trains run through it just fine, that’s also backwards since the standard is the “gold test”, not whether some train or cars will negotiate the curve.