Esquire-esque

[fender3x]

...On that train of thought - a 12" radius is where the circle would have a 12 inch radius - so any cylinder with a 24 inch diameter would make a good "reverse radius" to slap some sandpaper on..... like a large pot plant holder?????

Any cylinder with a 24" diameter would do it. Double sticky tape a piece of sandpaper on it and sand away. The plant should not even be bothered with it.

If you don't have a planter the right size but you do have a router, you can also use a circle jig to cut a 12" radius on a piece of scrap wood.

If you don't have a router...is this the sort of thing that men's sheds have? If I ever get to Australia, that will definitely be something I will visit. They exist in the US, but are not common. The nearest one to me is an hour and a half's drive...and is the only one in Florida.

[EsquireEsque]

Yes - I thought about routing a circle (or quarter circle) ... but it'd be a thick slab to be useful..... and a big one to make a circle

Men's sheds - yes I think there are about 3 or 4 within 5 to 10 minutes drive (probably more). Few are actually called "men's sheds" and will simply be "woodworking shops".... there are a number of women who will also turn up to make something.

(There is the one "celebrated" time when an old lady turned up... the guy running the shop was concerned for her safety.. and asked if she'd ever worked with wood before..... she replied "yes, I made a violin once"...from scratch!...)

We have the normal Machinery.... bandsaws, table saws, drop saws, sanding machines, thickenessers, jointers as well as a lot of both power and hand tools etc....."keeps us off the streets" - and for some of us, away from our wives!

I've thought of another use for your "reverse radius" technique.... Neck sockets.
slap some sandpaper on the heel of a neck and use that to sand a way at a very soft wood to make a jig for the neck socket.

Ear-marked for the next body that I'm making.....