A jig for finishing a workpiece with a handheld router or other handheld motor-driven rotational tool assembly is provided. The jig includes a baseplate that is precisely aligned and attached to a router. Guides, including a main guide and a support guide, are provided. The main guide is configured to precisely align with and fasten to the base plate in several different jig configurations. Right-angle adaptors attach to the guides and precisely align with and attach to the guides and the base plate to form several different jig configurations. Side plates secure the workpiece therebetween and provide a surface along which the main guide may slide to facilitate finishing operations on the workpiece.