Router Jig for Fluted Posts and Trim
With this simple jig, you can make a fluted post or pilaster door trim in any size or dimensions. Start with a piece of 1⁄2-in.-thick Baltic-birch plywood as wide as the base of your router and at least 18 in. long, to handle a workpiece 6 in. wide or less. Remove the baseplate from your router and, using the mounting screw holes as a guide, drill mounting holes in the plywood base. Now use a bandsaw or router to cut two slots in each end of the base, right up to the edge of the router location. Finally, drill a center hole in the base for the router bit.
Make two adjustable side blocks. To rout flutes in a square post, these blocks should be at least 1-1⁄2 in. thick. If you are making pilaster trim, the blocks should be the same height as the workpiece thickness, probably 3⁄4 in. The blocks need to be wide enough to extend under the router base so you can cut flutes near the edge of the workpiece. Install two hanger bolts near the outside edge of each block, spaced the same width as the slots in the base. Add a washer and wing nut to each bolt and the jig is complete.
To use the jig, simply position the router at the flute location, bring up the side blocks to the edges of the workpiece, and tighten the wing nuts to lock the side blocks. Make sure the jig slides freely but without any side-to-side play. Install a stop block at the beginning and end of each flute run for accuracy.