Popular Woodworking 2003-10 № 136, страница 36

Ingenious Jigs

deeper than V§" with each pass until you have cut through the wood.

Cutting an Oval

To rout an oval, you must swing the router around two movable pivots in an arrangement called a "double trammel." The pivots slide back and forth in their dovetail slots; one controls the length of the oval while the other controls the width.

To rout an oval, position the minor pivot over the center of the oval where the two slots cross.

Start by marking the center of the oval on your workpiece. Draw two lines at right angles that intersect at this point, then mark the length of the oval along one line and its width along the other.

Attach the oval pivot block to the work-piece with carpet tape, centering the slots over the lines you have drawn. Attach the router to the beam and align the beam with the major axis (length) of the oval.

Center the minor pivot (which is the pivot that moves along the minor axis, or width) and fasten the beam to it with a roundhead wood screw.

Next, swing the beam 90°, aligning it with the minor axis. Position the router so the bit is even with the mark for the minor axis, center the major pivot and attach the beam with a screw. The beam should not be fastened too tightly to either pivot.

To check your setup, swing the router once around the pivot block with the power off. The bit should pass over the end of the major and minor axes.

Once this is done, turn on your router, adjust the depth of cut for a shallow bite and swing the router around the pivots. As you rout, pull gently outward. The slight tension will take any play out of the mechanical system, helping to create a smooth, precise oval. Rout in multiple passes, cutting just a little deeper with each pass. PW

Position the router so the inside cutting edge of the bit (the edge nearest the center) is even with one end of the major axis, then attach the beam to the pivot by driving a roundhead screw through one of the predrilled holes. If none of the holes are aligned over the pivot, you must use a different diameter router bit or drill a new hole.

Repeat, centering the major pivot and aligning the inside cutting edge of the router bit with the mark for the minor axis. Note that the minor pivot has slid to the opposite side of the pivot block from the router.

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Popular Woodworking October 2003