How to Rout a Slot through the Center of a Workpiece
One of the quickest and easiest ways to rout a slot in the center of a workpiece is to use the router table, like you see in the photo below.
I started by laying out the length of the slot on the workpiece. Then, using a drill press, I drilled a ⅜" starter hole at one end of the layout, as shown in detail ‘a’ below. A second hole drilled at the other end marks the bottom of the slot.
After drilling the holes, you’re ready to move to your router table to finish the slot. The first thing to do here is to mount a straight bit in your router the same size as the starter holes you just drilled.
Next, align the fence so you can drop the starter hole over the bit. Since the bit will be covered, I added a piece of tape to the fence to mark the location of router bit.
I like to remove the material in increments. So I set my router to cut a depth of ¼". Then turn the router on and carefully lower the starter hole down over the bit, as illustrated below.
Using the layout lines as a guide, move the upright to the left along the fence. To avoid burn marks, move the upright with a constant steady motion. This will cut a shallow groove on the bottom side of the workpiece.
Stop the cut when you reach the mark on the fence or see the router bit enter the second hole. Then while holding the piece in place, turn off the router. Now you can raise the bit slightly, and repeat the process to deepen the slot. Continue making passes until you have cut all the way through.
Sources for some of the hardware and supplies mentioned in this tip.