Woodworker's Journal 2007-Winter, страница 59

Every woodworker knows that 3/4" is not really 3/4 of an inch, and virtually no two boards are exactly the same thickness. This makes milling snug-fitting dadoes difficult indeed, and it was the impetus for this adjustable dado jig.

While there are a number of tried-and-true methods for cutting perfectly sized dadoes, we wanted to be able to set a single straightedge and mill most any size dado needed — in just two passes. Our solution involves running two of the auxiliary base's edges along the straightedge. One edge is a fixed distance from the cutting edge of the bit, and the second can easily move in and out to adjust the final dado width.

Milling the Base Pieces

Begin by cutting 1/2" material to form the two plates (pieces 1 and 2) of the auxiliary base. It is important that the next step is exactly matched top to bottom, so stick the two parts together with double-sided tape. Lay out the mounting hole locations for your router on the face of the top plate so the cutting edge of your 1/2" straight bit will be exactly 3" from the fixed edge of the jig (see Elevation Drawings at left). Drill the mounting holes and the clearance hole for the bit through both layers. Separate the two parts and turn the top plate over to countersink the mounting holes and mill the dovetail slots, as shown at left. Next, mill the 1/4" adjustment slots through the top plate, along the centerlines of the dovetail slots.

Next, cut the lower plate in half, and bore the mounting holes out to 1/2" to provide , clearance for the mounting ^ screws. Glue the front half to the top plate to create the fixed edge of the jig. Then mill a shallow

Winter 2007 59

1/2"-wide dado in the movable base for a stick-on ruler (piece 3).

For safety, mill the hardwood dovetail slides (pieces 4) along one edge of a wider 1/2" board to fit the slots. Once they slide smoothly in the slots, trim them off on the table saw. To attach them, slip them into the slots, clamp the second half of the bottom plate to the rest, and screw (no glue) the half plate to the slides. Finally, with the movable base set flush, drill and tap the holes for the clamping knobs (pieces 5).

Using the Jig

Let's say you need a tight-fitting 19/32" dado, and you've got a 1/2" bit chucked in your router. To use the jig, first clamp your straightedge 3" from the desired edge of the dado. Use the tape measure to set the movable edge to 3/32" (the difference between the bit and the desired width of the dado). Tighten your knobs and

make the first pass with the movable edge riding along the straightedge. Spin the router around so the fixed edge is along the straightedge, and form the other wall of your dado — exactly 19/32" wide! Perfect dadoes every time. p

The second pass with this jig widens the dado for a perfectly snug fit.