I used this router jig to cut the circular dome base ring and ribs.  Do not skimp on the router bit.  Use a good quality carbide quarter-inch diameter by one-inch depth cutout bit.  I used a Craftsman router circle cutter adapter.  I replaced the short arm that came with the adapter with a long aluminum bar.  I drilled holes in the bar at the proper radius centers and used a nail as a pivot.  This rig worked quite well.