I suspect you'll want a bit with a guide bearing, or bearings on both top and bottom. The bit profile would depend on the shape/profile of the train's wheels.

http://eagleamerica.com/flute-cutterassembly-bits/p/164-1042/

http://eagleamerica.com/three-wingslot-cutters/p/146-0130/

In either case, the base of the router would ride on the flat side of the bridge, and the guide bearing would ride against the "rail" surface.

The curved track sections would be routed from the top surface, using a rounded V-shaped edge guide below the base plate of the router, keeping that at right angles to the (ever-changing) tangent of the curve, if working from the inside of the curve. A regular edge guide could be used if working from the outside of the curve, keeping the edge guide parallel to the changing tangent.

 

Hi,

I believe Rockler.com should carry what you're after. Give them a look see.

http://www.rockler.com/product.cfm?page=17231

 

Hi Guys

Just one more place to get them from , just a little bit cheaper


http://www.mlcswoodworking.com/shop....com/shopsite_sc/store/html/smarthtml/pages/bt_bull.html#train_track_bit_anchor

http://www.mlcswoodworking.com/shopsite_sc/store/html/smarthtml/graphics2/TM61-65-traintrack.pdf


This would be a good job for the ski jig to make the round tracks with the aid of a template


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I noticed the MLCS product page photo depicts the double-groove bit sitting on a section of curved track. I love it when manufacturers use photographers who don't understand the products, and art directors who don't catch the photographer's errors. Grrrr.

At least their instruction PDF makes it clear the double-groove bit is for straight track segments only.