Popular Woodworking 2003-10 № 136, страница 35
that cross at right angles in the middle of the block. To cut these slots accurately, first rout ordinary grooves with a straight bit to remove most of the stock. Then use a dovetail bit to create the angled shape. Cut the sliding pivot blocks to fit the dovetail slots, making them small enough to slide easily.
Depending on the size of the ovals you want to rout, you may have to adjust the size of the oval pivot block. I made mine 8" in diameter - this works well for a variety of small- and medium-sized ovals. To determine if this will work for you, subtract the minor axis of the oval (its width) from the major axis (its length). Add 1" to prevent the sliding pivots from slipping out of the slots, and that's the minimum diameter of the pivot.
Cutting a Circle
To rout a circle, position the circle pivot block in the center of your workpiece (shown at right) and attach it with double-faced carpet tape (so you won't have to drive a screw or a nail into your work and mar the surface).
Mount a straight bit in your router and attach the router to the beam. Drive a roundhead screw through the beam and into the center of the pivot block.
The distance from the screw to the edge of the bit should be equal to the radius of the
circle you want to cut. You can adjust this radius either by varying the diameter of the bit or drilling new holes in the beam.
Swing the router and the beam around the pivot clockwise, cutting your circle. Make the circle using several passes, routing no
When you mark the center of the circle on your work, draw a large crosshair. Fasten the circle pivot block to the work with carpet tape, aligning the corners with the arms of the crosshairs. This will center the block precisely.Attach the beam to the block and rout your circle.