All you need to make one of your own are scraps of hardboard and hardwood. Begin by sizing the hardboard for your router base. It should be big enough to support the whole thing. Next, make a hole matching your bit’s position and a little wider in diameter to make sure the bit has clearance. Finally, attach the hardwood fence. This determines the bit’s spacing from the edge, so make a test cut to be sure it’s on correctly.
Double-sided tape does the heavy lifting here, both on the base and fence. It’s strong, especially in terms of shearing, which is the main force applied while you press the fence against the edge. Turn on the router and let the fence guide you for a perfectly spaced cut.
