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Circles for the ground board, rings for the Upper Tube Assembly, the altitude bearings, the mirror box baffle and cover, as well as the arcs for the rocker box were cut with a router, as described in the Berry and Kriege book (Figures 6.6 and 6.7). I bought this Sears (model #917507 - about $110 on sale) PLUNGE router. It must be a plunge router so you can enter the wood at any point. To make the circles or arcs, you need to attach the router to an arm. The one shown in the Berry and Kriege book (page 159) is really nice, but I couldn't find the right size steel rod, so I bought a Sears accessory (model #925405 - about $12) designed to edge guide the router. I used a metal blade on my saber saw to cut the lip from the edge guide and drilled a 1/4" hole in the guide as seen here. This 1/4" hole takes a 1/4" bolt coming up from the bottom of the router table. A washer followed by a finger tight nut, lock washer and another (tight) nut holds the guide firmly in place. |
I used two thicknesses of the 3/4"-thick medium density fiber board for the table (left-overs from the altitude bearings). The router table is then firmly clamped to the table saw table with pipe clamps (not shown). One other modification had to be made. The router, when it is attached to the edge guide is held up about 1/4" off the surface of the table. I glued (Liquid Nails) formica onto one side of a piece of 1/4" ply and attached a curved piece to the bottom of the router with bolts. The threads for the bolts were already in place and the bolts used had tapered heads which were countersunk into the ply. With this attached the whole system is level and works great. The minimum radius you can cut is a bit under 3" and the maximum is about 11". To cut a circle just use a 1/4" straight bit designed for plunging. Carbide bits last significantly longer than steel bits and are worth the extra money.
