I have made a curved top for a letterbox by mitering and gluing the edges of narrow pieces. I've then used my spokeshave and sandpaper to get a smooth outside surface. I intended to smooth the inside using my round card scraper but have realized it's not really practical to take that amount of material off with a scraper.
There is a similar question here. My question differs in two ways. Firstly, I'm not asking specifically about 'old school' techniques. If someone has a way of doing it with a router then I'm all ears. Secondly, the suggestion of using a compass plane in the accepted answer wouldn't work for me as the curve is too tight and I would be planing against the grain. A scorp would probably be perfect for this but unfortunately I don't have one and would prefer not to get one for a single project.
Any other ideas for how to get it smooth?