SUBROADBED
The subroadbed of Free-mo modules is typically the module top, either extending across the full width of the module or following some form of a “cookie cutter” approach. The module framework and subroadbed are the foundations upon which good trackwork depends. While invisible in the finished module, finished trackwork will inevitably expose framework and sub-roadbed faults. Whether made of foam, plywood, splines or other material, the framework and sub-roadbed must satisfy the following:
This is extremely important and will cause continual problems if
ignored. Avoid use of MDF. MDF is very heavy, not particularly strong,
and is affected by humidity. A material you can’t go wrong with is high
ply-count Baltic or Finn birch plywood. It’s important to use material
of sufficient thickness for the frame member involved.
This 3-dimensional requirement is absolutely fundamental to successful
module creation.
1st
dimension:
End plates must be exactly perpendicular
to the subroadbed. It’s
essential to read and follow Gregg Fuhriman’s advice in
Appendix 2.
2nd
dimension:
The subroadbed (usually the module top) must be level from side-to-side
with the endplate.
At a setup either the track or the end
plate will be used to determine if a module is level. Out-of-level
subroadbed will force a twist in the track at the bridge rails or make
it impossible to match up the endplates nicely with adjoining modules.
3rd
dimension:
The subroadbed must not slope down or rise up at the module end.
A common module design has the top of the module extending to,
but not over, the top of the endplate. Any mismatch of the module top
and the top of the endplate will likely result in a problem.
If the top edge of the endplate is high relative to the module top, the
only solution is to reduce the top edge of the endplate. Failing to do
so will result in an upward rise in the track at the end of the module.
If the top edge of the endplate is low
relative to the module top, there simply isn’t a good solution. Sanding
the module top to match the endplate will result in a downward dip in
the track at the module end.
Example:
The distance from the pilot and the front truck kingpin of an Alco PA-1
or a super-detailed modern diesel is long enough that the pilot or
snowplow move up and down a lot as the locomotive travels through dips
and rises in trackwork. At a “V” shaped dip at a module joint, metal
pilots or plows can contact the track and cause a short.
Example:
The use of prototypical size couplers on long cars can result in
uncoupling as the couplers rise and fall relative to each other on track
that isn’t level through the bridge rails.
Example:
At a recent setup, a twist at the bridge rails resulted from a
difference in side-to-side leveling of the subroadbed even though the
endplates of the adjoining modules 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 pronounced.
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.
Support the subroadbed well and securely along its length to make sure
that it will stay flat and level over time. There are Free-mo modules
that are 15 years or more old and have been subjected to a lot of
handling and transportation. Some have held up well; others haven’t
lasted so well.
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
Remember that transitions in track level (e.g., from HO roadbed to N
roadbed or to the subroadbed) are grades and must be long and gradual.
See item 4 in the handbook section on roadbed.
[Track Design] [Contents] [Roadbed]
Gary M. Green
gary@regalvalley.com