ROADBED

I 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.

 1.      Use roadbed material that is resistant to expansion and contraction with humidity and temperature.

 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 when wet. Cork roadbed sealed with a coat of paint is a good solution.

 2.      Glue rather than nailing cork roadbed in place.

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 applying 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 weak 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 Sand Devil and uses a sanding belt that's used by belt sanders.

 

4.       Changes of roadbed levels must be very gradual.

Transitions 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 leading car dips 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 following car being lifted off the track and a derailment occurs. Even if the couplers were to slide freely, an uncoupling is still possible.

5.       Superelevation on curves presents special problems.

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.

Example: Out of curiosity, I tabulated the superelevation of all the curves in the ATSF Pasadena Subdivision in 1988 between MP 84 and MP 139. Note that some of this was 90 MPH territory. The results suggest that modelers often overdo superelevation.

 

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 be 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.

 6.      Drill holes for turnout actuating wire before laying track.

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.

Since the construction drawings were very precise, I was able to use a plunge router to create slots for actuating wires and clearance space for turnout throwbars in the plywood top of Mojave Yard.

 

7.       Pre-drill holes for track power feeder wires only if under-rail feeders are planned.

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.

 8.      Seal the roadbed before laying any track.

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.

 9.      Prepare for IR sensor installation.

The optional Free-mo Modular Signaling System includes IR detectors at 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.