This is my OpenSCAD design to generate a table saw rail guide. I have tried to parameterize almost every aspect of the design so that you can create just about any table saw rail guide as long as you can input the dimensions into the OpenSCAD file.
Particularly, the STL file I've uploaded works perfectly for my Craftsman portable table saw. I'm using the guides that I printed on a featherboard with screws and adjustable knobs that when tightened will cause the rail guide to expand and prevent slippage.
Most of the dimensions for my print are done with a 0.4mm clearance (0.2mm per side) on my Robo 3D, which worked perfectly. This will vary from printer to printer, so don't get frustrated if your first print is a little too large or small to fit your guide, it takes a very small amount of plastic.
Also, i'd like to attribute jacksonliam for providing his rCube module at http://www.thingiverse.com/thing:8812/#comment-380315