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I am going down future rabbit holes; thinking ahead about making a flat-top (radiused) mandolin. I see lots with oval/elliptical soundholes and rosettes and wondered how that is done. Some are hand cut, some use router bit templates (this would require changing the bit or template piece several times). I was hoping for something as easy as an adjustable circle-cutting jig. Lots of online references to Archimedes Trammel (AKA Ellipsograph, and other less-flattering) to draw it, and larger versions to cut one out, like a table top say.:

https://www.instructables.com/Trammel-of-Archimedes/;
https://woodarchivist.com/3372-elliptic ... jig-plans/

But my dim mind bogs down when I try to figure if one could be made that was adjustable equally in both directions, and mounted to a mini-router base, to make small rosettes. Anybody any experience? Bruce W.

Search for "Rockler Ellipse/Circle Cutting Jig". You would need something like that but smaller.
-David

Yes, I did come across the Rockler tool in my digging, and as you point out, it needs to be smaller. I wondered if it could be made to work to produce a much smaller ellipse, in the same way you used to (pre-digital aids) enlarge or reduce an image using a pantograph:

https://www.leevalley.com/en-ca/shop/to ... ograph-set

For all the hassle, and given the increasing availability of CNC products, it may be no surprise that no one has bothered to try! A round hole for my first mandolin is looking pretty appealing . . . Bruce W.

My friend Carter made an elliptical sound hole:
https://submusicworks.com/wordpress/wp- ... 8x1024.jpg
I'll inquire how he did it.