I like to use cork for the roadbed. After the track centerline is drawn on the sub-roadbed, it’s easy to carefully align one side of the cork with its center edge along the centerline of the track when gluing it down. Butting the other half of the cork against the first carries the centerline to the top of the cork roadbed so that it can be used when laying the track. At turnouts, each half to the cork roadbed can follow its respective track centerline, and the gap between filled with pieces of cork cut to fit.
As with subroadbed, this is extremely
important. Failure to do so
will introduce unpredictable results with trackwork itself and the
scenery that surrounds it. Ballasting and application of other scenery typically involves
water-based glues which will cause problems with materials that expand
Nails are likely to create dimples and dips in cork roadbed that may show when track is installed. Use flat boards and weights to hold the roadbed down as the glue is drying. I have been happy with the appropriate Liquid Nails adhesive.
Uneven application of adhesive can result in bumps in the roadbed. Gregg Fuhriman recommends using an adhesive spreader to assure that the adhesive is applied evenly. Following his advice, I use an inexpensive spreader with 1/16” x 1/16” teeth. Keeping the teeth clean is important so that the layer of adhesive is adequate. Use this spreader when spreading adhesive for track as well. One pass with the spreader will do it. Multiple passes with the spreader will reduce the amount of glue and may result in a weaker glue joint.
3. Roadbed must not introduce dips, rises and twists.
After the glue has dried, the installed roadbed can be sanded flat with a full piece of fine grain sandpaper wrapped the long way around a 12” long flat piece of 2” x 3” or 2” x 4” lumber. Sand very carefully and only enough to insure that the cork is flat and level all the way across the module. Be careful not to create any dips, rises or twists in the roadbed. An especially troublesome location is at the end of a module where the sanding block isn’t fully supported by the roadbed and rounding off the end of the roadbed is a risk. Don’t forget to round off the rough edges of the cork so that the ballast slope is smooth, but be careful not to alter the flatness of the top of the cork roadbed when doing so.
I've recently found a great sanding block that you might consider. It's long and very easy to use. It's called a SandDevil and uses a sanding belt that's used by belt sanders.
Example: One of the modules at a large setup had a twist and angular rise in the track partway through the module that could be observed only when sighting along the track at track level. One nicely detailed B-B diesel derailed regularly at that point.
Transitions, for example, between main line track on HO roadbed and lower level side tracks or spur tracks on N or no roadbed must be long and extremely gradual. Very large radius vertical curves are required. Keep in mind that 80-85 foot HO cars are about foot long. Changes in level that are too abrupt will result in derailments, coupler mismatches or other problems.
Example: The first car of a long, heavy passenger train derails as it exits a side track that is lower than the main track. The derailment occurs as the rear coupler of the car would naturally dip as the car enters the overly steep track leading up to the main track. Because the following train is heavy, the rear coupler of the car resists sliding against the coupler of the following car, resulting in the rear truck of the first car being lifted off the track and a derailment occurs. Even if the couplers were to slide freely, an uncoupling is still possible.
If you plan to superelevate your curves, there are a few things to keep in mind:
It’s the outer rail that’s raised, not the inner rail that’s dropped. The best way to accomplish this is to shim under the outer rail with strip wood when the track is installed. Don’t try to build superelevation into the roadbed since it’s nearly impossible to do so successfully. Remember that while prototypical superelevation may be as much as 5-6”, it is most often much less than that.
Out of curiosity, I tabulated the superelevation of all the
curves in the ATSF
Superelevation Frequency HO equivalent
None 5 --
½” to 1 15 0.0115”
1½” to 2” 15 0.0230”
2½” to 3” 10 0.0344” (~1/32”)
3½” to 4” 6 0.0459”
4½” to 5” 3 0.0574”
5½” to 6” 0 0.0689” (~1/16”)
The transition from level to superelevated track must very gradual. Superelevation introduces a twist into trackwork that will result in derailments of stiffer or longer equipment if the transition isn’t long and gradual. If you superelevate track, you’ll be asking the trucks of locomotives and cars to twist as they enter and leave superelevated track. Prototypical transitions extend at least through the length of the easement (typically long) and into the straight track as required to maintain a gradual transition. The elevated rail is held at a constant height throughout the constant radius curve itself. Model trackwork experts typically recommend a transition equal to twice the length of the longest cars that will be operated. For HO, that’s about two feet.
Example: On a short module incorporating superelevation, the length of the transitions to superelevation were so short that some C-C diesels and some passenger cars frequently derailed.
Unless you’re confident of your ability to incorporate superelevation correctly, skip it. Broad, smooth curves and trackwork will often lead observers to think that track is superelevated when it isn’t.
This takes careful planning but is impossible to do after track is laid. An oversize hole makes certain that you have room for the switch machine actuating wire.
Gregg Fuhriman’s technique is best. Drill a large hole in the subroadbed, lay the cork right over it, and then use an X-Acto knife or saw to make a narrow slot in the cork where the throw-rod of the turnout will be. All this will work only if the exact location of the turnout throw-bar has been clearly marked at its exact eventual location on the subroadbed ahead of time during the centerline drawing phase.
I used a plunge router to create slots for actuating wires and
clearance space for turnout throwbars in the plywood top of Mojave Yard.
I used a plunge router to create slots for actuating wires and clearance space for turnout throwbars in the plywood top of Mojave Yard.
While I don’t recommend it, this is the preferred method for some Free-mo modelers. I prefer to solder feeder wires to the outer side of rails after track is installed since planning hole locations for feeders before track is laid is difficult to do successfully. If you plan under-rail feeders, drill holes before laying track and make sure that they permit you to lay down the track exactly where you intend it to be.
I prefer to solder feeders to the outside of rails. There’s good advice on track feeders (and other subjects as well) in Easy Model Railroad Wiring by Andy Sperandeo.
This will extend the life of the cork or other material and will reduce if not eliminate shifting with temperature or humidity. Sealing with paint similar to the ballast color will also help disguise any areas where ballast is missed during application or damaged during handling.
The optional Free-mo occupancy detection system for signaling includes IR detectors at a block boundaries to provide detection of rolling stock that won’t be detected by current detectors. Installation of IR sensors is strongly recommended even if signals aren’t installed initially. Installation recommendations are included in Appendix 8 along with a more complete description of the occupancy and detection system.