Christopher Brimley updated May 27, 2011


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  • PVC Spline Roadbed

    by Bama Harman, MMR

    Photos by Miles Hale

    Model Railroading - October 2004 - Page 39

    Most sane model railroaders will look at a construction project and try to determine the easiest way to accomplish a satisfactory end result. Cost is also a consideration that sneaks into the projects planning phase early on. In the end, ease of construction will almost always increase actual construction costs. It is sad to say that in a lot of projects, the targeted satisfactory end result gets compromised instead. Sometimes the key to balancing the equation lies in the vast selections of building materials that are available today. Modeling in the space age does have its benefits. Just take a look at how I fixed the little problem I was having with humidity and temperature fluctuations showing up in my trackwork.

    I don't have a jillion dollars or the desire to turn my basement into a perfect environmental wonderland...and my kids never seem to remember to close doors anyway. The trackwork shrank, grew, twisted and did all sorts of spaghetti tricks throughout the year, as our notorious Midwest Ohio Valley climate unleashed its worst on my basement layout. Every time I wanted to run trains, Id find myself adjusting track to compensate for the distortions. No amount of expansion joints would have made any significant improvement on performance and reliability. I figured changing the weather is a tad bit beyond my capabilities, so dealing with the symptoms would be my best approach to having a reliable railroad in my current location. I finally got the chance to tackle the problem when I decided to switch to HOn3. The new trackplan required removal of a major portion of the existing layout. I decided to bite the bullet and rip out the rest, since I was already removing such a large portion anyway.

    Once the room was completely empty of anything closely resembling a model railroad, I made the final adjustments to my new track design on paper. I am fortunate enough to have access to a large format printer through my place of employment, and printed out the trackplan life size. This gave me the ability to see how the layout would actually fit within the room. Having full-sized plans also helps tremendously when building the benchwork. I covered the plans with a couple of layers of clear plastic drop-cloth material. This kept the plans protected, not to mention the wall-to-wall indoor/outdoor carpet.

    After constructing the basic L-girder framework to fit the layouts shape, I placed my joists as needed. Medium density overlay plywood (MDO) was used for the main yard and logging camp areas, but it became apparent that the multi-layered trackwork would need to be splined. MDO is a product used in the sign industry for outdoor applications where a sign needs to hold up to the elements. A smooth paper-like laminate gives the plywood a grain-free work surface, and its adhesives hold up to moisture quite well. Since the majority of the new layout was to be splined, my climate-affected concerns were focused on that portion of the overall construction. Needless to say, cost issues promptly came to bear, along with the aspects associated with the ease of construction.

    The old standard for splining a roadbed has been around for a long time. The idea is to laminate slats of material together into a shape that corresponds to the desired direction you want your track to follow. Because the slats are thin and pliable, they can be easily shaped in all dimensions, making life easy for those of us who like railroads that have lots of overlapping track. The problem with splines is in the choice of materials. Each material has its own drawbacks. Wood works great, but needs to be tight grained and relatively knot free. The ideal material should have a consistent density throughout. Wood does not have this feature. One end of the slat can be denser than the other, resulting in a non-concentric curve when bent into its desired shape. You also wind up with as much wood on the floor, in the form of sawdust, as you do in the pile of slats you just ripped on the table saw. Ive seen slats made from Masonite, Homasote, Plexiglas and Lexan. All have their own little problems. I had even read an article somewhere about some guy who used 1/2" plastic water pipe for splines! Remembering that article gave me my own set of ideas.

    Polyvinyl chloride is the base ingredient in PVC water pipe. This material is not only waterproof, but resists changes in temperature as long as they aren't drastic. The material can be glued, screwed, nailed, tapped, threaded and stapled. It can be cut with common hand tools and doesn't rust. The best part is its availability in sheet form. Standard sizes include 4' x 8' sheets in 1/16", 1/8", 1/4", 3/16", 1/2", 3/4", 1", and even thicker by special order. It even comes in colors!

    Model Railroading - October 2004 - Page 40

    While there is a cost increase over plywood, the ability to glue the material together quickly with ordinary PVC pipe cement, makes it a viable alternative to those materials already in use as splines. WARNING - follow the adhesives label and use proper ventilation. PVC glue has an extremely strong odor and is flammable. Don't fill your basement with fumes and then wonder why you blew the house off the foundation with the furnace pilot light. I PVC-splined my whole layout in just two myself. The first night I didn't ventilate and wound up walking into the edge of an open door while the wife was screaming at me over how bad the whole house smelled. There's no telling how many brain cells bit the dirt that night. The next evening I used a small portable window fan without any problems.

    I used a few simple tools to do the job (see Photo 2). I purchased the 1/4" material from a local plastic supplier. I salvaged the thicker pieces from the sign shop dumpster and used them for spacers. Yes...I admit to being a dumpster diver. Any large sign shop can get material for you as well. I ripped it into 11/2" tall slats on a table saw. The length doesn't matter, but I found the 4' lengths to be just right for my own application.Using a plumb bob (see Photo 3) I sized and placed my risers as needed. The photo depicts the trackplan drawn on the floor. My new layout is already scenicked and ripping it out a third time to do the article was not an option. Once the risers had been placed (see Photo 4), I added 1/2" thick spacer blocks directly over the centerline of the track; the blocks were attached to the top of the risers using drywall screws. I applied a generous coating of PVC cement and clamped the first of the two center splines onto the spacer blocks. Adjust the shape to match your trackplan by checking with the plumb bob. I added the other center spline next and made sure to add a few more 1 /2" spacer blocks between the two slats, to keep the pair spaced correctly from riser to riser (see Photo 5). It is important to use a square to make sure your splines remain level from side to side, unless you are modeling a section of super-elevated rail. The outer slats were added in the same way, except I used 1/4" spacer blocks to bring the overall width to 2" (see Photo 6). The 2" finish size is perfect for HO or HOn3 roadbed and track. Use whatever spacing you need to build larger gauge roadbed (see Photo 7).

    Notice how flexible the material is in Photo 1. Over time, the material will adopt the shape you form it to, lessening the tension in the overall assembly. This one key element is the major reason why the material holds its shape so well during changes in temperature. If you pull a material out of its usual shape, changes in climate will result in changes in the amount of force required to hold it in the new shape. The PVC material has a consistent texture and internal geometry so it bends in concentric arcs when needed. PVC is pliable enough to be formed on both the horizontal and vertical planes, and will produce smooth natural changes in any direction (see Photo 7). The transition from one direction to another is natural and does not have the abrupt appearance that ramp-style construction produces (see Photo 8).

    By now you can appreciate the speed with which the material can be joined. I used only six clamps to build my railroad. By the time I clamped six locations, the first joint was already dry, allowing me to leap frog the clamps as I went down the line. A dozen clamps would have been nicer, but the six worked just fine. Joining splines, end to end, is done by sharing spacer blocks. I cut a few spacer blocks a bit longer to allow enough room for joining slats together. I suggest staggering the joints across the spline, as well. Try not to have all the splines splice together at one point. If you do, it should be at a riser where you can maintain the shape better. When the spline assembly is dry, you will be surprised at how strong and stable the whole structure can be.

    Adding turnouts is handled by adding additional slats off the main run, until the diverging spline has enough slats to continue its own way. The 1/2" gap provides ample room for using the slow motion switch motors that are available today. I use both Switchmaster and Circuitrons Tortoises with no problem. I have found it easier to glue the motor directly to the splines than it is to use mounting screws, however an additional platform can also be used where motor placement proves problematic. Just glue a PVC platform directly to the bottom of the splines and go for it.

    Model Railroading - October 2004 - Page 41

    I decided to use Homasote for my roadbed. You can buy the stuff already cut, shaped and ready to install through most hobby shops. Im a tightwad and saved some money by making my own.

    I do not recommend using cork for roadbed with splines, unless you cookie cut an additional layer of PVC to support it. I hand spike my own rail so split cork just doesn't work well for me. Adding the Homasote is as easy as it comes. A good quality construction adhesive and those same six clamps are all that's needed to make it come together (see Photo 9). Notice the slices in the Homasote strips. They allow it to bend around the curves much like flextrack does. One hint...keep the slices to the inside of the curves where they will close tighter when bent or youll be spending a fortune on ballast. Give the Homasote a good coat of sealer and gloss latex paint before adding your track. Itll help prevent humidity/moisture problems later. If it soaks up water, then coat it with paint, or replace it with something that will repel water.

    Okay, so you are ready to add scenery and there is this rollercoaster looking bunch of track splines snaking all over the place. I 7 stapled wire mesh directly to the sides of the outer splines and formed it into the shape of the terrain I wanted. Standard hardshell construction techniques work very well with spline construction. In some areas I stapled the wire onto the sides of the Homasote, but only where the base layers of hardshell would insure a good bond later on. I have had the new layout for almost two years now, and have seen no appreciable climate-related track problems. Of course some of that may be contributed to my hollering at the kids to keep the doors shut. Its a learning curve thing.

    The use of splined roadbed is certainly not a new idea. I just adapted new materials to an old idea to make it better suited for my own use. Like most ideas that manage to pass muster and serve the hobby over time, they only get better with age. The advent of plastic technology has certainly made its mark on model railroading. Had I to do it over again, I would replace my wood framing with PVC plastic products as well.

    Here's what to look for when hunting the material locally. Ask for the material by its trade name - Komatex, Komacell or Sintra. It is an extruded PVC high-density foam sold in sheet form. Purchasing through a local user, such as a sign shop, can be cheaper than buying from the dealer since high-volume buyers often receive massive discounts. If you find a local user, raid their dumpsters for scraps. Sign shops often toss away scrap materials that are still adequate for our use. A quick search on the internet will also produce a source close by, but you may not get as good a bargain that way. Prices vary with thickness and seller. Ive seen it anywhere from $20 to $50 for a 4' x 8' sheet of 1/4" thick stock.

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