Fitted with a three-wing slotting cutter and mounted in a commercial biscuit joiner attachment, a router cuts semicircular slots for wood biscuits. Glued into two mating slots, the biscuits form a strong and durable plate joint—without the expense of a plate joiner. You can also cut the same joint on a router table with a simple shop-made setup, as shown below and on the following page. In fact, a table-mounted router can cut all the same joints as a biscuit joiner, including edge-to-edge, edge-to-face, and end-to – face joints. One exception is an edge-to – face joint in the middle of a panel, such as would typically be needed to install fixed shelves in a bookcase.
Plunging the workpiece into the bit
To rout biscuit slots for an end-to-face plate joint, as shown here and on page 95, start by slotting the end grain. Set up for the cut as you would for a double dado (page 90), installing a three-wing slotting cutter in the router and an auxiliary fence on the router table. Also screw a board to the miter gauge as an extension. Since the wood biscuits are longer than the bit diameter, you will need to feed the workpiece along the fence after plunging the bit into the stock. Draw a line across the fence centered above the cutter and mark the slot location on the workpiece centered between the edges. Measure the difference between the biscuit length and cutter diameter, and mark lines on each side of the centerline on the fence, offsetting each one by one-half the measured difference. To start the slot, butt the edge of the workpiece against the miter gauge extension with the end clear of the bit and align the slot location mark with the offset line on the infeed side of the fence (above). Then slide the board along the extension, plunging the end grain into the cutter.
Slotting the face of the mating board
Mark the slot location on the inside face of the work – piece (near the top end so you can see the mark when the board is flush against the fence). Hold the workpiece against the fence with the location mark aligned with the offset line on the infeed side of the fence, then butt the miter gauge against the edge of the board and clamp it in place. With the workpiece clear of the cutter, turn on the router. Pressing the edge of the board against the miter gauge, pivot the inside face toward the fence (left), plunging the bit into the stock. Once the board is flush against the fence, slowly slide it forward, keeping it pressed against the fence. Stop feeding the workpiece once the slot location mark aligns with the offset line on the outfeed side of the fence. Then turn off the router and pivot the board away from the fence.
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The jig shown at right will enable you to rout slots for wood biscuits using a hand-held router fitted with a top – piloted Узг-inch three-wing slotting cutter. Make the jig base from 14-inch plywood—long enough to accommodate the three notches and wider than the router base plate diameter. Cut the notches into the edges of the base, one for each biscuit size. On one edge, make a 1%-inch-long notch for No. 20 biscuits and on the opposite edge, a Г/б-inch-long notch for No. 10 biscuits and a ІУе-inch-long notch for No. 0 biscuits. Cut all the notches 1 inch deep; label each one and mark its center. To position the base squarely on a workpiece, cut four 1-inch – wide edge guides and glue one in each corner of the base, two per face.
To rout a slot, set your stock on a work surface and clamp the jig on top, aligning the center mark of the
appropriate notch with the slot location mark on the workpiece. Make sure the edge guides on the underside of the base are flush against the stock. With the router base plate flat on the jig base and the bit clear of the workpiece, turn
on the router. Cut the slot by guid ing the cutter along the bottom of the notch, starting with the pilot bearing pressed against one edge of the notch, riding it along the bottom and stopping when it contacts the opposite edge.