This variable dado fixture will allow fine adjustment of the dado width from bit diameter to double the bit diameter. The fixture works on the principle that one edge of the router base is farther from the bit than the other. To use, clamp a fence in place on the workpiece and make one pass with the wide side of the fixture against the fence. Turn the router around (narrow side to the fence) and make a second pass.

To make the fixture, cut a 9-in. square from 3/4-in. hardwood plywood and rout a 1/2-in. deep recess in the center to receive the router base. Rip one edge off the fixture and reattach it with two cleats, as shown. Slot one cleat to allow adjustment. The other cleat is fixed, and the adjustable edge is pinned to it so that the edge can pivot. You will have to trim the corner of the base outside the pivot point so that the adjustable edge won’t bind. After the fixture is attached to the router, check to be sure that the distance from the bit to the adjustable edge is slightly (1/16 in.) less than the distance to the fixed edge. If it isn’t, saw a little off. Otherwise, slight adjustments over bit size are impossible.

Jere Cary, Edmonds, Wash.

Fine Woodworking Magazine, October 1983 No. 42

Fine Woodworking Recommended Products

Leigh D4R Pro

The D4R Pro is Leigh’s flagship jig. Like the other Leigh jigs in our test, it represents a different world of quality, from its clear, comprehensive instructions to its ingenious engineering, impeccable manufacturing, and unmatched capabilities.

Buy at Amazon Buy at Woodcraft

Olfa Knife

Comfortable plastic handle with a break off blade. A tool for breaking off the blade is built into the handy pocket clip.

Buy at Amazon

Veritas Precision Square

This precision square is incredibly versatile, from checking squareness to dialing in machine setups.

Buy at Lee Valley