Here's my shop-made pin router, whcih I use to cut my spiral rosettes and soundholes. It's a Porter-Cable 310 laminate trimmer mounted in a Bishop Cochran plunge base, which is in turn mounted on a long plywood box. The box stands over the table, registered with a 1/4" bolt in each leg. There is a 1/8" pin mounted in the table, exactly under the router bit. The pin rides in a groove in a plastic template, which is mounted in a plywood board the size of a sound board. The template is a mirror image of the desired rosette shape, so that when a top is attached with double-sided tape to the board, the template pattern is duplicated onto the top. I register the top to the board with a 3d nail through the center point of the soundhole.
The router bit and the pin:
Closeup of the pin in the table:
The registration bolts, and the brass bushing lined holes the fit into:
The underside of the board with several templates set into it:
The top side of the board, showing circle cuts from routing the soundholes:
The pin router in action:
I cut the spalted wood rosette inlay on the pin router too, so I use a 3/32" router bit, the same size as the 5-line purfling I use. The inlay drops right in and the purfling fills the width of the rout.
The pin router can be used to replicate any shape of soundhole - Selmer D shape, archtop F-holes, ovals, spirals, whatever. It can also cut logos in head veneers, saddle slots in bridges, etc. Any shape you can draw and cut into a plastic template can be duplicated in wood.