John K Jordan
>>>I wonder if it would work with a 2" pipe

As long as the pipe is somewhat smaller than the sphere diameter it should work. Too small would be a problem (such as 1" pipe on a 4" sphere).

I called it a "tube gouge" but it is really a "tube scraper." Don't grind it to a sharp cutting edge all the way around or it will dig in at the leading edge. If sharpened the leading edge needs to be dulled. Mine little pipe had a rough burr from grinding which made an excellent scraper. I beveled the OD a bit but ID worked better when rough.

In practice the pipe is aimed at the center of the desired sphere and swung in an arc. It will scrape off the high spots and not touch any low spots. The higher spots will scrape more quickly so it will make a nice sphere. It will keep on scraping and make a smaller sphere if you continue scraping after the surface is spherical.

I don't think I would try shaping a larger sphere entirely with the pipe. I forget if I mentioned it but I think I first turned the wood down to an ugly roundish blob then used the pipe to refine the surface.

BTW, when I last posted about this 10 years ago a thoughtful gentleman made and sent to me a couple of sizes of nicely machined tube bits threaded to fit the shaft of a custom handle. (The story is longer than that.) I sure wish I hadn't lost his name. The circular edge was sharpened to perfection. That's when I discovered a sharp edge won't work. It worked OK when I softened the leading edge and left the trailing edge dull. I will probably work better if I burnish a bevel on the bottom edge, curled towards the inside.

JKJ