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I get lots of questions from my model railroad design clients, many new to layout construction, as to how to handle rail gaps and rail joiners. Here are a few best practices and tips that may be helpful.

Tip 1: Allow Room to Breath

With changes in seasons, temperature, and humidity rail expands and contracts. For this reason you need to leave gaps at your track joints or the rail may buckle. A gap of 1/16 of an inch every section or two will be more than adequate. Under NO circumstances do you want to solder the joints (with one exception which I’ll explain in a second), doing so defeats the entire purpose of installing the gaps in the first place. If you drop electrical feeders every other section or so, you’ll have more than enough electrical pick ups to power the layout so soldering the joiner for electrical continuity isn’t necessary. Again, don’t solder the joiners at your rail joints.

Tip 2: Joints on Curves

When you join rail sections on curves, particularly those of tighter radius, you’ll often find you have trouble getting a smoothly flowing connection that maintains the radius of your curve. The outward pressure of the rail at the joint often creates a kink. To get around this make up a longer, six foot section of flex track, on your workbench first and then take this piece to the layout to install on the curve. Take two sections of three foot flex track and lay them straight on your workbench. Insert the rail joiners and connect the two pieces (without a gap) forming a single six foot long, straight section. While this long section of track is still laying flat on your work bench solder the joiners. This is the only instance where I recommend soldering the joiners.

Photo of outward kink when rails are joined on a curve.

Tip 3: Joining Different Rail Sizes

Rail size is differentiated by what is called “code”. Common sizes are code 100, code 83, 70, 55, and 40. The code refers to the height of the rail. For example, code 83 is .083” tall. Sometimes it’s desirable to mix different track sizes, in other words join a section of one code rail to a rail of a different code. For instance, you may want code 83 on your main line and code 70 for your industrial tracks.

Example of a connection between code 70 and code 83 track.

Begin by sliding a joiner on the ends of the larger code rail. Next, insert the smaller code rail into the joiner. In most cases you’ll notice a fair amount of “slop” or looseness where the smaller rail sits in the larger sized joiner. Using pliers, pull the smaller rail upward until the rail heads are even. Temporarily wedge it in place with a toothpick or other shim. Solder the connection. All done!

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