Sub-roadbed is the foundation upon which good trackwork depends.  While invisible in the finished module, finished trackwork will inevitably expose each and every one of the sub-roadbed’s faults.  Whether made of foam, plywood, splines or other material, the sub-roadbed must satisfy the following:

 

1.      Use materials that are strong, stable, and resistant to expansion or contraction with humidity and temperature.  This is extremely important and will cause continual problems if ignored.

 

2.     Make certain that endplates are completely flat and perpendicular to the module track both vertically and horizontally.  This is absolutely fundamental to successful module creation.  It’s essential to follow Gregg Fuhriman’s advice in Appendix 2.

3.      Roadbed must be flat and level for six inches from the end of the module.  This means truly flat and truly level:

 

·        level from side-to-side with the endplate of the module.  This is important because at a setup either the track or the end plate will be used to determine of a module is level.  If the track and the end plate aren't level with each other, either a twist in the track will be forced at the bridge rails or the endplates won't match up nicely to the next module.

 

·        roadbed at each end of the module level with the roadbed at the other end.  Any twist of the subroadbed from one end of a module to the other will result in twist in the track at the fitter rails at one end of the module or the other.

 

Example:  At a recent setup, a twist at the bridge rails resulted from a difference in side-to-side leveling of the track even though the endplates were level with each other.  The result was that some C-C locomotives would derail since the twist across the bridge rails was so short and so pronounced.

 

·        no sloping down or rising up at the module end.  This is a problem that can easily sneak in if the sub-roadbed isn’t adequately supported or has been sanded or filled to match up to the end plates of the module.  The result will be a dip or a rise at module joints across the fitter rails.  Plows and other low hanging details can snag or, if they’re made of metal, cause a short on rails in a dip.  Couplers can mismatch in either dips or rises, especially with longer cars and newer, semi-scale couplers like Kadee #58s.

 

Example:  The distance from the pilot and the front truck kingpin on an Alco PA-1 is long enough that the pilot moves up and down quite a lot as the locomotive travels through dips and rises in trackwork.  At a “V” shaped dip at a module joint, the pilot contacts the track and causes a short.

 

4.      Unless there is a grade included in the module, the sub-roadbed should be flat and level across the length of the module.  Again, this means truly flat and truly level.  Use a straight edge and sight along the module to make sure that the sub-roadbed is truly flat.

 

5.      If there is a transition to a grade included in the module, employ vertical curves that are extremely gradual (very large radius) between the level and the inclined track.  Too abrupt a transition will result in derailments, mismatched couplers, and will look un-prototypical.  The steeper the grade, the longer the vertical curve needs to be.  If in doubt at all, make vertical curves of extremely large radius.  The Northern California Free-mo recommendation for vertical curves is described in Appendix 5.