Updating the progress on the St. Vrain River bridge project exhibit.

In the last few weeks a lot of progress has been accomplished on the sections. Nearly complete and ready for track installation we take a look at the methodology John uses in his design.

John Johnson has now invested many hours into the framing and section construction. Installing roadbed splines and framing for the bridge piers.

Roadbed spline construction shown below

A look at the completed framework

John wrote an essay into the methodology of his module section design.

Lightweight Module Construction by John Johnson

A little history here will explain why this type of module construction came to be. Forty years ago N Trak was breaking a lot of new ground with the idea of modular layouts. They could be set up and displayed in many venues previously unavailable, like shopping malls. The hobby shop with the layout in the front window was getting rare and shopping malls were the the new meccas of retail trade. A lot of modeler got their start with these groups.

My club at the time was building a HO layout based on Marin County railroads in an old dairy barn. We decided to build a modular layout to display at the county fair. Construction was based on the N Trak standards, 1x4s with 1/2” plywood top. Sturdy but not very light. Legs were an issue as it was difficult to prevent swaying when they were leaned upon without getting involved with a lot of bracing. I even drilled lightning holes in th 1x4 crossmembers (actually 1/2”x4” plywood) in an effort to cut some weight. Later the 2x2” legs were replaced with 3/4” EMT conduit with angle braces to improve stability. Both efforts were marginal improvements.

My next effort was based on 1/4” plywood. Sides and ends were laminated with extra plys where the strength was needed. Legs were folding 2x2s. Not bad, it was lighter and easier to set up but still not quite right.

With my move to Colorado and switching to 1/4” scale came the opportunity to start over. Everything module effort to date had multiple toos problems:
too heavy
too fragile
too difficult to set up

Experimenting with a portable F scale layout introduced some new ideas. First to go was the legs, simple sawhorses under the joints replaced attached legs. Set up time was dramatically reduced. Next to go was the bolts/C clamps tyeing the modules together.

We use spring clamps w/ locating dowels between sections, quick and easy.

Actual module is 2″ insulation extruded foam (not white beaded stuff) that comes in pink or blue, depending on manufacturer. Default module width is 22″. Beam strength is provided by 2 3/4″ strip of 5mm underlayment plywood on each side. End boards a 3/4″ lumber to provide strength for dowels & clamps. Stringers of 3/4x3/4 wood are used about every 12″ to control sag between sides. This is where the 2 3/4″ side depth comes from. Titebond used for wood/wood joints, foam/wood joints are secured w/ our secret ingredient, Gorilla glue! This results in a bonded structure that resists twisting and bending. A 5′ module will support my weight in the middle (165#) with very little sag. A bare module weights appox 5#. #12 bare copper busses are strung under the track for feeders, SAE 4 prong plugs (trailer connectors) connect each module. Two Pony 2404 or equivalent spring clamps grip lower lip at joints where a lightweight sawhorse supports the joint.

Two plywood boxes (24x24x40″) were added to the center of each side of our 9x35′ layout for added stability. A casual bump doesn’t phase it. They also serve as control stands and power centers. A fixed clamp joins two modules on top and electrical connectors tie into the buss.

We will work on making a video of the construction process. Construction time is about an hour of actual work, added time for glues to set. Assembly is done on a fixture to insure squareness and assist clamping. Further questions can be submitted to our website:, contact us form.

Setup time for 16 modules is about an hour for one person, longer with help. Track ends at module edge, rails are soldered to screws or nails in the sub-roadbed (spline). This method has been in service for over a year (5 shows) w/o any problems.

John Johnson co/chair of Colorado O Scale Modelers

Erik will soon begin the phase he enjoys most, he will begin producing the scenery and river detail. The prospect of seeing a lone SD9 pulling a short local through this 10′ S curve through the finest in hand built brass bridges will be enough to stir and imagination for both the young and old alike. Documenting history in 1/4 scale is not only exciting for us; it also brings a museum level exhibit of 1940’s-1950’s Colorado Front Range branch line railroading up front and center stage for the community to enjoy.