The concept is simple: a straightedge is clamped on top of the workpiece, parallel to its edge. A template guide is screwed into the base of the router, and rides against the straightedge so the router moves in a perfectly straight path. A straight bit is chucked in to the router, and cuts the edge of the wood at 90 degrees to its face.
- Take a quick test cut (or measure) to determine the offset between the template guide and the router bit. In this case it's about 1/8”. Clamp the straightedge at both ends of the workpiece in a position that will lead to a full-length cut along the board. Also be sure whatever supports the board (in my case, sawhorses) won't be exposed to the router bit.
- Make light passes, which in this case means lowering the bit between passes. I found it went easiest if I took about 1/2” vertical cut per pass.
- After the first edge is jointed, mark a line parallel to it as a guide for clamping down your straightedge as you joint the second edge. That way your finished board will be a parallelogram instead of an irregular trapezoid. I used my fancy panel gauge because I like it and I don't get to use it very often, but a pencil against the end of an adjustable square is just as good.
- Clamp down your straightedge and joint the second edge.
- Clean up! One disadvantage compared to a jointer is that this spews dust everywhere!
- Test your results with an accurate square, to be sure you'll get a flat glueup. Assuming you generated nice flat faces by following the instructions in the post on how to get flat boards without a wide jointer, you should be fine, but it's foolish not to test your work before you roll on the glue and clamp it up!