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The S_Mod System of Module Railroading

The S-Mod System of Module Railroading

By Don Thompson and Don DeWitt

Part 2

Reprints from "The Herald" by permission of author.

Adapted for the WWW by Paul Yorke

The first installment in this series dealt with theories of planning and laying out a module. Now to the actual building of the platform upon which the track work will be attached. The method described in this series allows an infinite number of sizes to be built. It will also develop woodworking skills in the modeler. The tools are simple and the work is not difficult, but it does require the ability to cut a straight line. Now, if we haven't scared you away, let's begin Chapter II: Benchwork.


We are going to construct a switching module in three sections. These sections will be nearly identical, except for joiners as described below. Let's begin with a description of the module.

Each section is 64" long. When joined together, they form a module 16' in length. When stacked, they will fit into most cars with rear doors and collapsible seats. Since the overall length is 16', the complete module will fit into a layout that also has four 4' sections on the opposite side, allowing a loop to be assembled.

The module will have a double track mainline, but it could he built with single line. As built, it could be used as a stand-alone switching layout, or it could be part of a larger home layout. We decided on three sections (rather than four) to make turnout location less critical. And, as a bonus, we also eliminate one set of bridge rails.

The frame's stringers, cross-braces and transoms are made of 1x3" lumber. The legs are 2x2" pieces ripped from 2x4"s (more on this later). A complete list of materials for the three sections appears on the main drawing, as does a glossary of terms.

Let's get started

Begin by cutting the wood. Be sure to get dry, straight lengths of lumber that are as free from knots as possible. If you have access to a furniture wood supplier, you might try to obtain lengths of maple or oak. Bear in mind that the frame and supports are really pieces of furniture that are going to he leaned on, moved around and bumped. It behooves the builder to use the best materials available in order to ensure a long and useful life.

Follow the list on the main drawing and when all the parts are finished we are ready to begin assembly. We should mention now that good, square cuts are essential for a well-constructed module frame.

We use #6 and #8 dry wall screws because they do not need predrilled holes and they will not split the wood. (On harder woods - such as maple - starter holes may he necessary.) They work well with an electric screwdriver and a phillips head bit. If these are not available, or if you prefer, the equivalent countersunk wood screw is as functional. However, you will have to predrill the holes.

We use wood glue in addition to the screws in order to get the tightest joints possible. Nothing can be more frustrating than working on a wobbly module. With a little care during construction, the finished product should support fifty or so pounds of layout without swaying.

It is best to work on a large flat surface. A 4x8' sheet of plywood laid on a table or workbench is an ideal work surface. The floor is another, but using it requires a lot of stooping.

Assembling the Frame

Following the plan in FIG 2, lay the 1 x 3 x 62" stringers on their sides and mark off the locations of the cross members. To be sure that the cross members will be square when assembled, lay out the holes on both stringers at the same time. We begin by placing one of the stringers so that its three inch side is vertical. After applying wood glue to one end of a 1 x 3 x 28 1/2" cross member, attach it to the stringer with drywall screws at one of the locations previously marked. Repeat this step until all of the cross members are attached to the stringer. Now attach the other ends of the cross members to the second stringer using the same procedure. A carpenter's square or a known-to-be-square piece of plywood is of great value in ensuring true 90-degree angles.

Once the cross members are in place, we can install the 1 x 3 x 30" transoms. These are the pieces that close the box, and they mount over the ends of the stringers. The same glue-and-screw procedure is used to secure them in place. Check to be sure that the frame is square and, if so, set it aside and work on the other two. Once all are completed it is best to leave them undisturbed while the glue sets. We've got plenty to do on the decks anyway.

Cutting the Deck and Roadbed Levels

The deck or sub-roadbed covers the frame entirely and is made of 3/8" plywood. A module that is designed for open roadbed where the plywood is used only under the tracks would require thicker (1/2" or better) material for rigidity. Use "good one side" which becomes the top surface. The roadbed will be attached to this surface later. Where dampness is a problem, use exterior grade plywood.

Cut three pieces 30x64" and sand the edges as necessary. It's recommended that the edges and bottom be sealed after cutting in order to prevent warping. (The frame and legs will be painted for the same reason.)

The roadbed covers the deck completely and is cut to exactly the same dimensions. Homosote is used here and, as this material is moisture-sensitive, both sides and all edges should be thoroughly sealed. A waterproof version of Homosote (identified by its green color) can also be substituted. For designs where the roadbed is open, the Homosote can be cut to fit or

pre-cut, shaped roadbed can be obtained from Bo Manufacturing (RD3, Box 375B, Kingston, NY 12401). They make a 3/8" thick product that is quite useful for this purpose. Another possibility is the blue extruded Styrofoam that builders use to insulate houses. It can be glued to the deck with Liquid Nails and has the advantage of being waterproof and will not warp.

Once the deck and roadbed levels are cut and checked, they should he sealed as mentioned above. They may require more than one coat, and sufficient drying time should be allowed between applications.

The Legs

There are many ways to make legs and attach them to module sections. The most common is to use 2x2s ripped from 2x4 studs. (The reason for this can be seen at any builder's supply. Most 2x2s look like an Irish shillelagh, with maybe one in a hundred being straight.) They should be cut so the top of the rail is 42" from the floor. (This is for S scale. In other scales the standard rail height may vary, so its best to check the appropriate standards to determine the correct rail height.) Slight variations in floors or leg mounting errors are corrected for by using adjusting screws or furniture levelers in the bottoms of the legs.

Whatever the scale you are using, the following formula will apply:

Leg Length = R(h) + T(t) + Rb(t) + D(t) - S(h) +/- V

This equates to: Rail (h)eight + Tie (t)hickness + Roadbed (t)hickness + Deck (t)hickness - Standard (h)eight above the floor. V is the adjusting bolt explained below.

The drawing for the legs and the leveling screws.

For example, if the rail is code .125, (1/8"), the ties are 1/8" thick, the roadbed is 1/2" thick and the deck is 3/8" thick, then the legs should be 40 7/8" long. However, to allow for variations in floor levels and leg mounting techniques, we use adjusting bolts that have 1" of travel, or 1/2" in either direction. Therefore, the final length of the leg is 40 3/8" which will give us our 42" rail height with 1/2" of adjustment possible in either direction.

Assembling the Sections

Place one of the frames flat on the work surface. As shown in FIG 1, position one of the legs in the interior corner formed by a stringer and the first cross member from either end. (Notice that the leg is not positioned in a corner formed by a transom and a stringer, as this area must be kept clear to accommodate the C-clamps that will join the sections together.) Once the leg is positioned squarely in the corner and flush with the work surface, clamp it firmly in place and drill two 5/16" holes through the stringer, using the holes in the leg as a guide. Repeat this process for the other 3 legs. It is a good idea to temporarily assemble the legs to the sections at this time to ensure that they will fit. When this is done, sand all surfaces as necessary and apply a coat of the porch paint everywhere except the top edge of the frame. (The deck will be glued and screwed to this surface.)

After the paint is dry, we are ready to install the deck and roadbed. Lay the frame on the work surface with the unpainted edges facing up. Run a bead of glue onto all of these edges. Then place the plywood deck on top of the frame and begin screwing it in place using the drywall screws. A starter hole may be necessary, but we have found that the drywall screws generally go in easily and countersink themselves.A screw every eight or so inches should be sufficient. Take care that no screw heads protrude above the deck surface, as they will prevent the roadbed from laying flat.

When this is done the Homosote layer is applied in much the same manner, except that glue is applied all over the deck surface and screws are only used on the peripheral edges.

When all the surfaces are in place and the glue is dry, the sections are ready for a final check before we start laying track. It is important that the decks of adjoining sections fit smoothly together, but it is more important that the transoms butt against each other without any interference from the deck and roadbed edges. Inspect the transom ends of each section to see that no deck surface protrudes over the edge. If so, remove it with a rasp, plane or sandpaper. Now install the legs on one unit and level them so that the roadbed top is 41 3/4" from the floor. (The remaining 1/4" is the combined rail and tie height.) When this is done, assemble the legs to one end of the next section and join the other end to one end of the first unit using a C-clamp in each corner. Adjust the levelers in the bottoms of the legs as necessary. Repeat this procedure one more time to join to last section to the first two.

We are now ready to lay track, which will be the subject of the next installment.

Continue to Part 3

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