One way to make a jig or accessory adjustable is to use fasteners in slots. So over the years, I’ve made a lot of slots. The process I use to create perfect slots takes place at the router table with an ordinary straight bit and a quick-and-easy layout.
Before heading to the router table, lay out and drill starter holes at both ends of each slot you’re going to cut. Besides being used as entry points for the router bit, the starter holes make it easy to position the router table fence and a pair of stop blocks used to control the cut. Once the holes are drilled, you can set up your router table to cut the slots. Position one of the holes you drilled over the router bit (with the workpiece oriented in the direction you’ll cut the slot). After sliding the fence up against the workpiece, lock it down. With the workpiece still in place, position a stop block at the edge of the workpiece that’s furthest from the bit.
Then reposition your workpiece so the second hole is over the bit. And once again, attach a stop block at the opposite edge of the workpiece.
At this point, you’re ready to start routing. You’ll want to take multiple passes to work your way through the thickness of the workpiece. (I take about 1⁄4" per pass.) Turn on the router and brace the workpiece against one of the stops. Pivot it down over the bit and simply slide it between the two stop blocks. After raising the bit, repeat the process.
