Flutes are long grooves cut into wood for aesthetics. They are usually 3/8 or 1/2 inch wide and 1/4 to 1/2 inch deep with round sides created by bullnose router bits. Flutes are common on colonial-style architecture and can be found on columns or furniture legs or mantles. Flutes are cut parallel with each other and need to be exact to establish uniformity and clean lines associated with fluted columns. Router fluting jigs can be used to get the flutes straight and coordinated with each other.
Making the Jig
Install a 3/4-inch dado blade on a table saw. Lower the blade down below the surface of the table.
Set the table saw fence at 1 5/8 inch from the blade. Place the poplar board on the table saw. The board should extend over the blade to a point 12 inches past the blade.
Turn on the saw. Hold the board down with one hand while you crank the lever to bring up the blade. Hang on tight until the blade emerges up through the top of the blade. Push the blade forward and stop when you get within 12 inches from the end of the board. Shut off the saw. Lower the blade beneath the table.
Slide the fence over to 2 1/4 inches from the blade and lock it down. Repeat step 3 to cut another dado beside the first.
Nail two blocks on both ends of the board with a pin nailer where you wish the flutes to stop. For example, for 48-inch flutes, nail two blocks on the board 48 inches apart.
Using the Jig
Insert a 1/2-inch flute bit into a hand router. Set the depth at 3/8 inch. Install a 1/4-inch bushing in the router base; the bit will pass directly through it.
Clamp the jig to the face of a piece of lumber with one clamp on both ends. Insert the router bit into one of the dados in the jig. Let the router base rest on the jig. Turn on the router. Pull the router down the dado; the bushing will follow the dado and cut the flute into the wood.
Release the clamp. Slide the jig over so that the second dado lines up with the flute underneath it. Clamp the jig on again and route another flute. It will be perfectly positioned beside the first. Repeat this step as many times as desired.
Use the sharpest router bit you can find. Don't stop moving when routing a flute or you could burn the flute. Practice on a piece of scrap wood to get the feel for it.
Always wear safety glasses when working with wood. It the wood starts to splinter when you are routing a flute, pick up on the router and start over in a different place. Come back later to finish where the splinter had previously emerged.