I`m finishing up a 6" f/10.5 dob following the plans in The Dobsonian Telescope. I cut the bottom board circles using a jig saw by hand and then used the router with a homemade circle guide to make the final pass. I found that it worked almost as effectively as using the router alone. For the side bearings, I used cabinet grade plywood and cut with the router. However, I cut from one side only and kept turning the piece to allow overhang off the table when the bit cut through. Naturally, the plywood wasn`t screwed to the table. I just screwed the circle guide to the wood at the center of the circle.