T-nuts and wheel offer precise router elevation
Put your table-mounted router on this device and you can dial in your elevation changes with incredible precision. Start with a piece of 3⁄4 " stock and cut out the round pad that the router rests on. Use a Forstner bit to bore a 3⁄4 "-diameter hole in the center 1⁄2 " deep. Then, drill a 3⁄8 " hole through the center.
Insert the threaded rod into the hole in the pad and secure it, as shown, with a pair of washers and nuts. Make the threaded rod long enough to raise and lower your router about 2" when sitting in the table. Next, secure the wooden adjustment wheel just above the middle of the rod using a nut, washer, and T-nut where shown in the Section View drawing. With epoxy, glue the T-nut to the threaded rod.
Finally, install a plywood base about 3" up from the bottom of your table legs, insert a T-nut in the base, and screw the bottom of the threaded insert into the T-nut. Now, when you turn the wheel, the whole assembly rides up or down on the T-nut in the plywood base. By using a threaded rod with 16 threads per inch, you move the router 1⁄16 " for every full turn of the wheel, 1⁄32 " for each half turn, and so on.
—Duane Abels, Vancouver, Wash.