Routing Wooden Spheres
Last Christmas, I wanted to give my wife a sphere covered with 1/2-in.-sq. mirrors. Styrofoam was my first thought, but a plastic ball would have cost $32, so I decided to make one from wood, and devised this simple router fixture to do it. First, glue up a rough sphere by laminating graduated discs of plywood or solid wood; the larger discs should be rings, to save weight and material. Drill a hole through the north and south poles so that the blank can be mounted on a threaded-rod axle inside a box frame, as shown in the sketch. Washers serve as shims to center the blank in the frame.
The outside frame is just wider than the box frame, which pivots inside it on two mounting bolts. The sphere should rotate smoothly within the box frame; the box frame should turn smoothly within the outside frame. Center a router on a platform so that the bit is suspended over the sphere.
To rout the sphere, first clamp the fixture to the bench. Then rotate the rough sphere to find its high spot, and set the router bit a little lower than this. Turn on the router and rotate the sphere inside the box frame, occasionally pivoting the box frame a little within the outside frame. Continue lowering the router bit until the sphere is true. Except for a small area at each pole, the router bit can reach every point on the sphere. The small flat spots at the poles can easily be rounded off by hand.
Frank D. Hart, Plainfield, Ind.
Fine Woodworking Magazine, February 1984 No. 44