We bought a 500 year old house with lovely beams that weren?t so lovely as they had been painted black. I tried all sorts of stuff on a small test area, stripper chemicals, sandpaper, sand blasting (with a power hose and sand bucket adapter thing) and none worked well or was sooooooo slow it was too frustrating. The ?paint? was bitumen an runny plaster (to fill the holes I think) and layers of different paint.
In the end, what worked best was a drill with a carbon or nylon stripping wheel. It took ages, was very messy but was the fastest and didn?t harm the oak. I then had to get into the corners with a wire brush and sandpaper.
Good luck!