With typical profiling router bits such as ogees, coves or chamfers, if a workpiece moves away from the fence, there’s no real harm done. You make another pass to remove what you missed. Same goes if you don’t get the stock pressed down quite as tightly to the table as necessary. Cleanup passes fix the problem. That’s not the case with some bits, such as dovetails or T-slot cutters. Here, if the workpiece moves either away from the fence or up and off the table, the cut is ruined. That’s because the bit is trapped inside the workpiece where its entire profile is impacting the cut.
In these situations, a pair of featherboards is essential — one over the top and one alongside the workpiece. Kreg offers a convenient pairing with its True-FLEX™ Featherboard Twin Pack ($36.99 in 2010). One featherboard has T-slot hardware to apply downward pressure over a router table fence. The other featherboard has a pair of miter bars with a unique wedge lock that expands them for a tight grip. I found these particularly easy to tighten in place when compared with some other miter bar styles.